MyBatis的动态SQL详解
2016-12-01 17:34
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<div class="blog_main">
<div class="blog_title">
<h3>
<a href="/blog/1338557">MyBatis的动态SQL详解</a>
<em class="actions"> </em>
</h3>
<ul class="blog_categories"><strong>博客分类：</strong> <li><a href="/category/131096">mybatis</a></li> </ul>
<div class="news_tag"><a href="http://www.iteye.com/blogs/tag/MyBatis">MyBatis</a><a href="http://www.iteye.com/blogs/tag/%E5%8A%A8%E6%80%81">动态</a><a href="http://www.iteye.com/blogs/tag/SQL">SQL</a><a href="http://www.iteye.com/blogs/tag/where">where</a><a
href="http://www.iteye.com/blogs/tag/foreach">foreach</a> </div>
</div>
<div id="blog_content" class="blog_content">
<div style="font-size: 14px;" class="iteye-blog-content-contain">
<p><a href="/blog/1333271">http://haohaoxuexi.iteye.com/blog/1333271</a></p>
<p> </p>
<p>MyBatis的动态SQL是基于OGNL表达式的，它可以帮助我们方便的在SQL语句中实现某些逻辑。</p>
<p>MyBatis中用于实现动态SQL的元素主要有：</p>
<p> </p>
<ul>
<li>if</li>
<li>choose（when，otherwise）</li>
<li>trim</li>
<li>where</li>
<li>set</li>
<li>foreach</li>
</ul>
<div>
<strong>if</strong>就是简单的条件判断，利用if语句我们可以实现某些简单的条件选择。先来看如下一个例子：</
4000
div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%3Cselect%20id%3D%22dynamicIfTest%22%20parameterType%3D%22Blog%22%20resultType%3D%22Blog%22%3E%0A%09%09select%20*%20from%20t_blog%20where%201%20%3D%201%0A%09%09%3Cif%20test%3D%22title%20!%3D%20null%22%3E%0A%09%09%09and%20title%20%3D%20%23%7Btitle%7D%0A%09%09%3C%2Fif%3E%0A%09%09%3Cif%20test%3D%22content%20!%3D%20null%22%3E%0A%09%09%09and%20content%20%3D%20%23%7Bcontent%7D%0A%09%09%3C%2Fif%3E%0A%09%09%3Cif%20test%3D%22owner%20!%3D%20null%22%3E%0A%09%09%09and%20owner%20%3D%20%23%7Bowner%7D%0A%09%09%3C%2Fif%3E%0A%09%3C%2Fselect%3E"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span class="tag"><</span><span class="tag-name">select</span><span> </span><span class="attribute">id</span><span>=</span><span
class="attribute-value">"dynamicIfTest"</span><span> </span><span class="attribute">parameterType</span><span>=</span><span class="attribute-value">"Blog"</span><span> </span><span class="attribute">resultType</span><span>=</span><span class="attribute-value">"Blog"</span><span
class="tag">></span><span> </span></span></li><li><span> select * from t_blog where <span class="attribute">1</span><span class="attribute-value">1</span><span> = 1 </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"title != null"</span><span class="tag">></span><span> </span></span></li><li><span> and <span
class="attribute">title</span><span> = #{title} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"content != null"</span><span class="tag">></span><span> </span></span></li><li><span> and <span
class="attribute">content</span><span> = #{content} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"owner != null"</span><span class="tag">></span><span> </span></span></li><li><span> and <span
class="attribute">owner</span><span> = #{owner} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span><span
class="tag"></</span><span class="tag-name">select</span><span class="tag">></span><span> </span></span></li></ol></div><pre name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#"
pre_index="0" title="MyBatis的动态SQL详解" style="display: none;">
<select id="dynamicIfTest" parameterType="Blog" resultType="Blog">
select * from t_blog where 1 = 1
<if test="title != null">
and title = #{title}
</if>
<if test="content != null">
and content = #{content}
</if>
<if test="owner != null">
and owner = #{owner}
</if>
</select></pre>
</div>
<div>这条语句的意思非常简单，如果你提供了title参数，那么就要满足title=#{title}，同样如果你提供了Content和Owner的时候，它们也需要满足相应的条件，之后就是返回满足这些条件的所有Blog，这是非常有用的一个功能，以往我们使用其他类型框架或者直接使用JDBC的时候， 如果我们要达到同样的选择效果的时候，我们就需要拼SQL语句，这是极其麻烦的，比起来，上述的动态SQL就要简单多了。</div>
<div> </div>
<div>
<strong>choose</strong>元素的作用就相当于JAVA中的switch语句，基本上跟JSTL中的choose的作用和用法是一样的，通常都是与when和otherwise搭配的。看如下一个例子：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%3Cselect%20id%3D%22dynamicChooseTest%22%20parameterType%3D%22Blog%22%20resultType%3D%22Blog%22%3E%0A%09%09select%20*%20from%20t_blog%20where%201%20%3D%201%20%0A%09%09%3Cchoose%3E%0A%09%09%09%3Cwhen%20test%3D%22title%20!%3D%20null%22%3E%0A%09%09%09%09and%20title%20%3D%20%23%7Btitle%7D%0A%09%09%09%3C%2Fwhen%3E%0A%09%09%09%3Cwhen%20test%3D%22content%20!%3D%20null%22%3E%0A%09%09%09%09and%20content%20%3D%20%23%7Bcontent%7D%0A%09%09%09%3C%2Fwhen%3E%0A%09%09%09%3Cotherwise%3E%0A%09%09%09%09and%20owner%20%3D%20%22owner1%22%0A%09%09%09%3C%2Fotherwise%3E%0A%09%09%3C%2Fchoose%3E%0A%09%3C%2Fselect%3E"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span class="tag"><</span><span class="tag-name">select</span><span> </span><span class="attribute">id</span><span>=</span><span
class="attribute-value">"dynamicChooseTest"</span><span> </span><span class="attribute">parameterType</span><span>=</span><span class="attribute-value">"Blog"</span><span> </span><span class="attribute">resultType</span><span>=</span><span class="attribute-value">"Blog"</span><span
class="tag">></span><span> </span></span></li><li><span> select * from t_blog where <span class="attribute">1</span><span class="attribute-value">1</span><span> = 1 </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">choose</span><span class="tag">></span><span> </span></span></li><li><span> <span class="tag"><</span><span class="tag-name">when</span><span> </span><span
class="attribute">test</span><span>=</span><span class="attribute-value">"title != null"</span><span class="tag">></span><span> </span></span></li><li><span> and <span
class="attribute">title</span><span> = #{title} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">when</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">when</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"content != null"</span><span class="tag">></span><span> </span></span></li><li><span> and <span
class="attribute">content</span><span> = #{content} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">when</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">otherwise</span><span class="tag">></span><span> </span></span></li><li><span> and <span class="attribute">owner</span><span> = </span><span
class="attribute-value">"owner1"</span><span> </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">otherwise</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"></</span><span class="tag-name">choose</span><span class="tag">></span><span> </span></span></li><li><span><span class="tag"></</span><span class="tag-name">select</span><span class="tag">></span><span> </span></span></li></ol></div><pre
name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="1" title="MyBatis的动态SQL详解" style="display: none;">
<select id="dynamicChooseTest" parameterType="Blog" resultType="Blog">
select * from t_blog where 1 = 1
<choose>
<when test="title != null">
and title = #{title}
</when>
<when test="content != null">
and content = #{content}
</when>
<otherwise>
and owner = "owner1"
</otherwise>
</choose>
</select></pre>
</div>
<div>when元素表示当when中的条件满足的时候就输出其中的内容，跟JAVA中的switch效果差不多的是按照条件的顺序，当when中有条件满足的时候，就会跳出choose，即所有的when和otherwise条件中，只有一个会输出，当所有的我很条件都不满足的时候就输出otherwise中的内容。所以上述语句的意思非常简单， 当title!=null的时候就输出and titlte = #{title}，不再往下判断条件，当title为空且content!=null的时候就输出and content =
#{content}，当所有条件都不满足的时候就输出otherwise中的内容。</div>
<div> </div>
<div>
<strong>where</strong>语句的作用主要是简化SQL语句中where中的条件判断的，先看一个例子，再解释一下where的好处。</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%3Cselect%20id%3D%22dynamicWhereTest%22%
20000
20parameterType%3D%22Blog%22%20resultType%3D%22Blog%22%3E%0A%09%09select%20*%20from%20t_blog%20%0A%09%09%3Cwhere%3E%0A%09%09%09%3Cif%20test%3D%22title%20!%3D%20null%22%3E%0A%09%09%09%09title%20%3D%20%23%7Btitle%7D%0A%09%09%09%3C%2Fif%3E%0A%09%09%09%3Cif%20test%3D%22content%20!%3D%20null%22%3E%0A%09%09%09%09and%20content%20%3D%20%23%7Bcontent%7D%0A%09%09%09%3C%2Fif%3E%0A%09%09%09%3Cif%20test%3D%22owner%20!%3D%20null%22%3E%0A%09%09%09%09and%20owner%20%3D%20%23%7Bowner%7D%0A%09%09%09%3C%2Fif%3E%0A%09%09%3C%2Fwhere%3E%0A%09%3C%2Fselect%3E%0A"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span class="tag"><</span><span class="tag-name">select</span><span> </span><span class="attribute">id</span><span>=</span><span
class="attribute-value">"dynamicWhereTest"</span><span> </span><span class="attribute">parameterType</span><span>=</span><span class="attribute-value">"Blog"</span><span> </span><span class="attribute">resultType</span><span>=</span><span class="attribute-value">"Blog"</span><span
class="tag">></span><span> </span></span></li><li><span> select * from t_blog </span></li><li><span> <span class="tag"><</span><span class="tag-name">where</span><span
class="tag">></span><span> </span></span></li><li><span> <span class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"title != null"</span><span
class="tag">></span><span> </span></span></li><li><span> <span class="attribute">title</span><span> = #{title} </span></span></li><li><span> <span
class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span class="tag"><</span><span class="tag-name">if</span><span> </span><span
class="attribute">test</span><span>=</span><span class="attribute-value">"content != null"</span><span class="tag">></span><span> </span></span></li><li><span> and <span
class="attribute">content</span><span> = #{content} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"owner != null"</span><span class="tag">></span><span> </span></span></li><li><span> and <span
class="attribute">owner</span><span> = #{owner} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"></</span><span class="tag-name">where</span><span class="tag">></span><span> </span></span></li><li><span><span class="tag"></</span><span class="tag-name">select</span><span class="tag">></span><span> </span></span></li></ol></div><pre
name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="2" title="MyBatis的动态SQL详解" style="display: none;">
<select id="dynamicWhereTest" parameterType="Blog" resultType="Blog">
select * from t_blog
<where>
<if test="title != null">
title = #{title}
</if>
<if test="content != null">
and content = #{content}
</if>
<if test="owner != null">
and owner = #{owner}
</if>
</where>
</select>
</pre>
</div>
<div> where元素的作用是会在写入where元素的地方输出一个where，另外一个好处是你不需要考虑where元素里面的条件输出是什么样子的，MyBatis会智能的帮你处理，如果所有的条件都不满足那么MyBatis就会查出所有的记录，如果输出后是and 开头的，MyBatis会把第一个and忽略，当然如果是or开头的，MyBatis也会把它忽略；此外，在where元素中你不需要考虑空格的问题，MyBatis会智能的帮你加上。像上述例子中，如果title=null， 而content != null，那么输出的整个语句会是select
* from t_blog where content = #{content}，而不是select * from t_blog where and content = #{content}，因为MyBatis会智能的把首个and 或 or 给忽略。</div>
<div> </div>
<div>
<strong>trim</strong>元素的主要功能是可以在自己包含的内容前加上某些前缀，也可以在其后加上某些后缀，与之对应的属性是prefix和suffix；可以把包含内容的首部某些内容覆盖，即忽略，也可以把尾部的某些内容覆盖，对应的属性是prefixOverrides和suffixOverrides；正因为trim有这样的功能，所以我们也可以非常简单的利用trim来代替where元素的功能，示例代码如下：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%3Cselect%20id%3D%22dynamicTrimTest%22%20parameterType%3D%22Blog%22%20resultType%3D%22Blog%22%3E%0A%09%09select%20*%20from%20t_blog%20%0A%09%09%3Ctrim%20prefix%3D%22where%22%20prefixOverrides%3D%22and%20%7Cor%22%3E%0A%09%09%09%3Cif%20test%3D%22title%20!%3D%20null%22%3E%0A%09%09%09%09title%20%3D%20%23%7Btitle%7D%0A%09%09%09%3C%2Fif%3E%0A%09%09%09%3Cif%20test%3D%22content%20!%3D%20null%22%3E%0A%09%09%09%09and%20content%20%3D%20%23%7Bcontent%7D%0A%09%09%09%3C%2Fif%3E%0A%09%09%09%3Cif%20test%3D%22owner%20!%3D%20null%22%3E%0A%09%09%09%09or%20owner%20%3D%20%23%7Bowner%7D%0A%09%09%09%3C%2Fif%3E%0A%09%09%3C%2Ftrim%3E%0A%09%3C%2Fselect%3E"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span class="tag"><</span><span class="tag-name">select</span><span> </span><span class="attribute">id</span><span>=</span><span
class="attribute-value">"dynamicTrimTest"</span><span> </span><span class="attribute">parameterType</span><span>=</span><span class="attribute-value">"Blog"</span><span> </span><span class="attribute">resultType</span><span>=</span><span class="attribute-value">"Blog"</span><span
class="tag">></span><span> </span></span></li><li><span> select * from t_blog </span></li><li><span> <span class="tag"><</span><span class="tag-name">trim</span><span> </span><span
class="attribute">prefix</span><span>=</span><span class="attribute-value">"where"</span><span> </span><span class="attribute">prefixOverrides</span><span>=</span><span class="attribute-value">"and |or"</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"title != null"</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="attribute">title</span><span> = #{title} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"content != null"</span><span class="tag">></span><span> </span></span></li><li><span> and <span
class="attribute">content</span><span> = #{content} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"owner != null"</span><span class="tag">></span><span> </span></span></li><li><span> or <span
class="attribute">owner</span><span> = #{owner} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"></</span><span class="tag-name">trim</span><span class="tag">></span><span> </span></span></li><li><span><span class="tag"></</span><span class="tag-name">select</span><span class="tag">></span><span> </span></span></li></ol></div><pre
name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="3" title="MyBatis的动态SQL详解" style="display: none;">
<select id="dynamicTrimTest" parameterType="Blog" resultType="Blog">
select * from t_blog
<trim prefix="where" prefixOverrides="and |or">
<if test="title != null">
title = #{title}
</if>
<if test="content != null">
and content = #{content}
</if>
<if test="owner != null">
or owner = #{owner}
</if>
</trim>
</select></pre>
</div>
<div> </div>
<div>
<strong>set</strong>元素主要是用在更新操作的时候，它的主要功能和where元素其实是差不多的，主要是在包含的语句前输出一个set，然后如果包含的语句是以逗号结束的话将会把该逗号忽略，如果set包含的内容为空的话则会出错。有了set元素我们就可以动态的更新那些修改了的字段。下面是一段示例代码：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%3Cupdate%20id%3D%22dynamicSetTest%22%20parameterType%3D%22Blog%22%3E%0A%09%09update%20t_blog%0A%09%09%3Cset%3E%0A%09%09%09%3Cif%20test%3D%22title%20!%3D%20null%22%3E%0A%09%09%09%09title%20%3D%20%23%7Btitle%7D%2C%0A%09%09%09%3C%2Fif%3E%0A%09%09%09%3Cif%20test%3D%22content%20!%3D%20null%22%3E%0A%09%09%09%09content%20%3D%20%23%7Bcontent%7D%2C%0A%09%09%09%3C%2Fif%3E%0A%09%09%09%3Cif%20test%3D%22owner%20!%3D%20null%22%3E%0A%09%09%09%09owner%20%3D%20%23%7Bowner%7D%0A%09%09%09%3C%2Fif%3E%0A%09%09%3C%2Fset%3E%0A%09%09where%20id%20%3D%20%23%7Bid%7D%0A%09%3C%2Fupdate%3E"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span class="tag"><</span><span class="tag-name">update</span><span> </span><span class="attribute">id</span><span>=</span><span
class="attribute-value">"dynamicSetTest"</span><span> </span><span class="attribute">parameterType</span><span>=</span><span class="attribute-value">"Blog"</span><span class="tag">></span><span> </span></span></li><li><span> update t_blog </span></li><li><span> <span
class="tag"><</span><span class="tag-name">set</span><span class="tag">></span><span> </span></span></li><li><span> <span class="tag"><</span><span class="tag-name">if</span><span> </span><span
class="attribute">test</span><span>=</span><span class="attribute-value">"title != null"</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="attribute">title</span><span> = #{title}, </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"content != null"</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="attribute">content</span><span> = #{content}, </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"owner != null"</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="attribute">owner</span><span> = #{owner} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"></</span><span class="tag-name">set</span><span class="tag">></span><span> </span></span></li><li><span> where <span class="attribute">id</span><span> = #{id} </span></span></li><li><span><span
class="tag"></</span><span class="tag-name">update</span><span class="tag">></span><span> </span></span></li></ol></div><pre name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#"
pre_index="4" title="MyBatis的动态SQL详解" style="display: none;">
<update id="dynamicSetTest" parameterType="Blog">
update t_blog
<set>
<if test="title != null">
title = #{title},
</if>
<if test="content != null">
content = #{content},
</if>
<if test="owner != null">
owner = #{owner}
</if>
</set>
where id = #{id}
</update></pre>
</div>
<div> 上述示例代码中，如果set中一个条件都不满足，即set中包含的内容为空的时候就会报错。</div>
<div> </div>
<div>
<strong>foreach</strong>的主要用在构建in条件中，它可以在SQL语句中进行迭代一个集合。foreach元素的属性主要有item，index，collection，open，separator，close。item表示集合中每一个元素进行迭代时的别名，index指定一个名字，用于表示在迭代过程中，每次迭代到的位置，open表示该语句以什么开始，separator表示在每次进行迭代之间以什么符号作为分隔符，close表示以什么结束，在使用foreach的时候最关键的也是最容易出错的就是collection属性，该属性是必须指定的，但是在不同情况下，该属性的值是不一样的，主要有一下3种情况：</div>
<div>
<ol>
<li>如果传入的是单参数且参数类型是一个List的时候，collection属性值为list</li>
<li>如果传入的是单参数且参数类型是一个array数组的时候，collection的属性值为array</li>
<li>如果传入的参数是多个的时候，我们就需要把它们封装成一个Map了，<strong>当然单参数也可以封装成map</strong>，实际上如果你在传入参数的时候，在MyBatis里面也是会把它封装成一个Map的，map的key就是参数名，所以这个时候collection属性值就是传入的List或array对象在自己封装的map里面的key</li>
</ol>
<div>下面分别来看看上述三种情况的示例代码：</div>
<div>1.单参数List的类型：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%3Cselect%20id%3D%22dynamicForeachTest%22%20resultType%3D%22Blog%22%3E%0A%09%09select%20*%20from%20t_blog%20where%20id%20in%0A%09%09%3Cforeach%20collection%3D%22list%22%20index%3D%22index%22%20item%3D%22item%22%20open%3D%22(%22%20separator%3D%22%2C%22%20close%3D%22)%22%3E%0A%09%09%09%23%7Bitem%7D%0A%09%09%3C%2Fforeach%3E%0A%09%3C%2Fselect%3E"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span class="tag"><</span><span class="tag-name">select</span><span> </span><span class="attribute">id</span><span>=</span><span
class="attribute-value">"dynamicForeachTest"</span><span> </span><span class="attribute">resultType</span><span>=</span><span class="attribute-value">"Blog"</span><span class="tag">></span><span> </span></span></li><li><span> select * from t_blog where id in </span></li><li><span> <span
class="tag"><</span><span class="tag-name">foreach</span><span> </span><span class="attribute">collection</span><span>=</span><span class="attribute-value">"list"</span><span> </span><span class="attribute">index</span><span>=</span><span class="attribute-value">"index"</span><span> </span><span
class="attribute">item</span><span>=</span><span class="attribute-value">"item"</span><span> </span><span class="attribute">open</span><span>=</span><span class="attribute-value">"("</span><span> </span><span class="attribute">separator</span><span>=</span><span
class="attribute-value">","</span><span> </span><span class="attribute">close</span><span>=</span><span class="attribute-value">")"</span><span class="tag">></span><span> </span></span></li><li><span> #{item} </span></li><li><span> <span
class="tag"></</span><span class="tag-name">foreach</span><span class="tag">></span><span> </span></span></li><li><span><span class="tag"></</span><span class="tag-name">select</span><span class="tag">></span><span> </span></span></li></ol></div><pre
name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="5" title="MyBatis的动态SQL详解" style="display: none;">
<select id="dynamicForeachTest" resultType="Blog">
select * from t_blog where id in
<foreach collection="list" index="index" item="item" open="(" separator="," close=")">
#{item}
</foreach>
</select></pre>
</div>
<div> 上述collection的值为list，对应的Mapper是这样的</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Java代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=public%20List%3CBlog%3E%20dynamicForeachTest(List%3CInteger%3E%20ids)%3B"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-j"><li><span><span class="keyword">public</span><span> List<Blog> dynamicForeachTest(List<Integer> ids); </span></span></li></ol></div><pre
name="code" class="java" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="6" title="MyBatis的动态SQL详解" style="display: none;">public List<Blog> dynamicForeachTest(List<Integer> ids);</pre>
</div>
<div> 测试代码：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Java代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%40Test%0A%09public%20void%20dynamicForeachTest()%20%7B%0A%09%09SqlSession%20session%20%3D%20Util.getSqlSessionFactory().openSession()%3B%0A%09%09BlogMapper%20blogMapper%20%3D%20session.getMapper(BlogMapper.class)%3B%0A%09%09List%3CInteger%3E%20ids%20%3D%20new%20ArrayList%3CInteger%3E()%3B%0A%09%09ids.add(1)%3B%0A%09%09ids.add(3)%3B%0A%09%09ids.add(6)%3B%0A%09%09List%3CBlog%3E%20blogs%20%3D%20blogMapper.dynamicForeachTest(ids)%3B%0A%09%09for%20(Blog%20blog%20%3A%20blogs)%0A%09%09%09System.out.println(blog)%3B%0A%09%09session.close()%3B%0A%09%7D"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-j"><li><span><span class="annotation">@Test</span><span> </span></span></li><li><span><span class="keyword">public</span><span> </span><span
class="keyword">void</span><span> dynamicForeachTest() { </span></span></li><li><span> SqlSession session = Util.getSqlSessionFactory().openSession(); </span></li><li><span> BlogMapper blogMapper = session.getMapper(BlogMapper.<span
class="keyword">class</span><span>); </span></span></li><li><span> List<Integer> ids = <span class="keyword">new</span><span> ArrayList<Integer>(); </span></span></li><li><span> ids.add(<span
class="number">1</span><span>); </span></span></li><li><span> ids.add(<span class="number">3</span><span>); </span></span></li><li><span> ids.add(<span class="number">6</span><span>); </span></span></li><li><span> List<Blog> blogs = blogMapper.dynamicForeachTest(ids); </span></li><li><span> <span
class="keyword">for</span><span> (Blog blog : blogs) </span></span></li><li><span> System.out.println(blog); </span></li><li><span> session.close(); </span></li><li><span>} </span></li></ol></div><pre
name="code" class="java" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="7" title="MyBatis的动态SQL详解" style="display: none;">
@Test
public void dynamicForeachTest() {
SqlSession session = Util.getSqlSessionFactory().openSession();
BlogMapper blogMapper = session.getMapper(BlogMapper.class);
List<Integer> ids = new ArrayList<Integer>();
ids.add(1);
ids.add(3);
ids.add(6);
List<Blog> blogs = blogMapper.dynamicForeachTest(ids);
for (Blog blog : blogs)
System.out.println(blog);
session.close();
}</pre>
</div>
<div> </div>
<div>2.单参数array数组的类型：</div>
</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%3Cselect%20id%3D%22dynamicForeach2Test%22%20resultType%3D%22Blog%22%3E%0A%09%09select%20*%20from%20t_blog%20where%20id%20in%0A%09%09%3Cforeach%20collection%3D%22array%22%20index%3D%22index%22%20item%3D%22item%22%20open%3D%22(%22%20separator%3D%22%2C%22%20close%3D%22)%22%3E%0A%09%09%09%23%7Bitem%7D%0A%09%09%3C%2Fforeach%3E%0A%09%3C%2Fselect%3E%0A"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span class="tag"><</span><span class="tag-name">select</span><span> </span><span class="attribute">id</span><span>=</span><span
class="attribute-value">"dynamicForeach2Test"</span><span> </span><span class="attribute">resultType</span><span>=</span><span class="attribute-value">"Blog"</span><span class="tag">></span><span> </span></span></li><li><span> select * from t_blog where id in </span></li><li><span> <span
class="tag"><</span><span class="tag-name">foreach</span><span> </span><span class="attribute">collection</span><span>=</span><span class="attribute-value">"array"</span><span> </span><span class="attribute">index</span><span>=</span><span class="attribute-value">"index"</span><span> </span><span
class="attribute">item</span><span>=</span><span class="attribute-value">"item"</span><span> </span><span class="attribute">open</span><span>=</span><span class="attribute-value">"("</span><span> </span><span class="attribute">separator</span><span>=</span><span
class="attribute-value">","</span><span> </span><span class="attribute">close</span><span>=</span><span class="attribute-value">")"</span><span class="tag">></span><span> </span></span></li><li><span> #{item} </span></li><li><span> <span
class="tag"></</span><span class="tag-name">foreach</span><span class="tag">></span><span> </span></span></li><li><span><span class="tag"></</span><span class="tag-name">select</span><span class="tag">></span><span> </span></span></li></ol></div><pre
name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="8" title="MyBatis的动态SQL详解" style="display: none;">
<select id="dynamicForeach2Test" resultType="Blog">
select * from t_blog where id in
<foreach collection="array" index="index" item="item" open="(" separator="," close=")">
#{item}
</foreach>
</select>
</pre>
</div>
<div> 上述collection为array，对应的Mapper代码：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Java代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=public%20List%3CBlog%3E%20dynamicForeach2Test(int%5B%5D%20ids)%3B"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-j"><li><span><span class="keyword">public</span><span> List<Blog> dynamicForeach2Test(</span><span
class="keyword">int</span><span>[] ids); </span></span></li></ol></div><pre name="code" class="java" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="9" title="MyBatis的动态SQL详解" style="display:
none;">public List<Blog> dynamicForeach2Test(int[] ids);</pre>
</div>
<div> 对应的测试代码：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Java代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%40Test%0A%09public%20void%20dynamicForeach2Test()%20%7B%0A%09%09SqlSession%20session%20%3D%20Util.getSqlSessionFactory().openSession()%3B%0A%09%09BlogMapper%20blogMapper%20%3D%20session.getMapper(BlogMapper.class)%3B%0A%09%09int%5B%5D%20ids%20%3D%20new%20int%5B%5D%20%7B1%2C3%2C6%2C9%7D%3B%0A%09%09List%3CBlog%3E%20blogs%20%3D%20blogMapper.dynamicForeach2Test(ids)%3B%0A%09%09for%20(Blog%20blog%20%3A%20blogs)%0A%09%09%09System.out.println(blog)%3B%0A%09%09session.close()%3B%0A%09%7D"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-j"><li><span><span class="annotation">@Test</span><span> </span></span></li><li><span><span class="keyword">public</span><span> </span><span
class="keyword">void</span><span> dynamicForeach2Test() { </span></span></li><li><span> SqlSession session = Util.getSqlSessionFactory().openSession(); </span></li><li><span> BlogMapper blogMapper = session.getMapper(BlogMapper.<span
class="keyword">class</span><span>); </span></span></li><li><span> <span class="keyword">int</span><span>[] ids = </span><span class="keyword">new</span><span> </span><span class="keyword">int</span><span>[] {</span><span
class="number">1</span><span>,</span><span class="number">3</span><span>,</span><span class="number">6</span><span>,</span><span class="number">9</span><span>}; </span></span></li><li><span> List<Blog> blogs = blogMapper.dynamicForeach2Test(ids); </span></li><li><span> <span
class="keyword">for</span><span> (Blog blog : blogs) </span></span></li><li><span> System.out.println(blog); </span></li><li><span> session.close(); </span></li><li><span>} </span></li></ol></div><pre
name="code" class="java" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="10" title="MyBatis的动态SQL详解" style="display: none;">
@Test
public void dynamicForeach2Test() {
SqlSession session = Util.getSqlSessionFactory().openSession();
BlogMapper blogMapper = session.getMapper(BlogMapper.class);
int[] ids = new int[] {1,3,6,9};
List<Blog> blogs = blogMapper.dynamicForeach2Test(ids);
for (Blog blog : blogs)
System.out.println(blog);
session.close();
}</pre>
</div>
<div> </div>
<div>3.自己把参数封装成Map的类型</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%3Cselect%20id%3D%22dynamicForeach3Test%22%20resultType%3D%22Blog%22%3E%0A%09%09select%20*%20from%20t_blog%20where%20title%20like%20%22%25%22%23%7Btitle%7D%22%25%22%20and%20id%20in%0A%09%09%3Cforeach%20collection%3D%22ids%22%20index%3D%22index%22%20item%3D%22item%22%20open%3D%22(%22%20separator%3D%22%2C%22%20close%3D%22)%22%3E%0A%09%09%09%23%7Bitem%7D%0A%09%09%3C%2Fforeach%3E%0A%09%3C%2Fselect%3E"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span class="tag"><</span><span class="tag-name">select</span><span> </span><span class="attribute">id</span><span>=</span><span
class="attribute-value">"dynamicForeach3Test"</span><span> </span><span class="attribute">resultType</span><span>=</span><span class="attribute-value">"Blog"</span><span class="tag">></span><span> </span></span></li><li><span> select * from t_blog where title like "%"#{title}"%" and id in </span></li><li><span> <span
class="tag"><</span><span class="tag-name">foreach</span><span> </span><span class="attribute">collection</span><span>=</span><span class="attribute-value">"ids"</span><span> </span><span class="attribute">index</span><span>=</span><span class="attribute-value">"index"</span><span> </span><span
class="attribute">item</span><span>=</span><span class="attribute-value">"item"</span><span> </span><span class="attribute">open</span><span>=</span><span class="attribute-value">"("</span><span> </span><span class="attribute">separator</span><span>=</span><span
class="attribute-value">","</span><span> </span><span class="attribute">close</span><span>=</span><span class="attribute-value">")"</span><span class="tag">></span><span> </span></span></li><li><span> #{item} </span></li><li><span> <span
class="tag"></</span><span class="tag-name">foreach</span><span class="tag">></span><span> </span></span></li><li><span><span class="tag"></</span><span class="tag-name">select</span><span class="tag">></span><span> </span></span></li></ol></div><pre
name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="11" title="MyBatis的动态SQL详解" style="display: none;">
<select id="dynamicForeach3Test" resultType="Blog">
select * from t_blog where title like "%"#{title}"%" and id in
<foreach collection="ids" index="index" item="item" open="(" separator="," close=")">
#{item}
</foreach>
</select></pre>
</div>
<div>上述collection的值为ids，是传入的参数Map的key，对应的Mapper代码：</div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Java代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=public%20List%3CBlog%3E%20dynamicForeach3Test(Map%3CString%2C%20Object%3E%20params)%3B"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-j"><li><span><span class="keyword">public</span><span> List<Blog> dynamicForeach3Test(Map<String, Object> params); </span></span></li></ol></div><pre
name="code" class="java" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="12" title="MyBatis的动态SQL详解" style="display: none;">public List<Blog> dynamicForeach3Test(Map<String, Object> params);</pre>
<div> 对应测试代码：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Java代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%40Test%0A%09public%20void%20dynamicForeach3Test()%20%7B%0A%09%09SqlSession%20session%20%3D%20Util.getSqlSessionFactory().openSession()%3B%0A%09%09BlogMapper%20blogMapper%20%3D%20session.getMapper(BlogMapper.class)%3B%0A%09%09final%20List%3CInteger%3E%20ids%20%3D%20new%20ArrayList%3CInteger%3E()%3B%0A%09%09ids.add(1)%3B%0A%09%09ids.add(2)%3B%0A%09%09ids.add(3)%3B%0A%09%09ids.add(6)%3B%0A%09%09ids.add(7)%3B%0A%09%09ids.add(9)%3B%0A%09%09Map%3CString%2C%20Object%3E%20params%20%3D%20new%20HashMap%3CString%2C%20Object%3E()%3B%0A%09%09params.put(%22ids%22%2C%20ids)%3B%0A%09%09params.put(%22title%22%2C%20%22%E4%B8%AD%E5%9B%BD%22)%3B%0A%09%09List%3CBlog%3E%20blogs%20%3D%20blogMapper.dynamicForeach3Test(params)%3B%0A%09%09for%20(Blog%20blog%20%3A%20blogs)%0A%09%09%09System.out.println(blog)%3B%0A%09%09session.close()%3B%0A%09%7D%0A"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-j"><li><span><span class="annotation">@Test</span><span> </span></span></li><li><span><span class="keyword">public</span><span> </span><span
class="keyword">void</span><span> dynamicForeach3Test() { </span></span></li><li><span> SqlSession session = Util.getSqlSessionFactory().openSession(); </span></li><li><span> BlogMapper blogMapper = session.getMapper(BlogMapper.<span
class="keyword">class</span><span>); </span></span></li><li><span> <span class="keyword">final</span><span> List<Integer> ids = </span><span class="keyword">new</span><span> ArrayList<Integer>(); </span></span></li><li><span> ids.add(<span
class="number">1</span><span>); </span></span></li><li><span> ids.add(<span class="number">2</span><span>); </span></span></li><li><span> ids.add(<span class="number">3</span><span>); </span></span></li><li><span> ids.add(<span
class="number">6</span><span>); </span></span></li><li><span> ids.add(<span class="number">7</span><span>); </span></span></li><li><span> ids.add(<span class="number">9</span><span>); </span></span></li><li><span> Map<String, Object> params = <span
class="keyword">new</span><span> HashMap<String, Object>(); </span></span></li><li><span> params.put(<span class="string">"ids"</span><span>, ids); </span></span></li><li><span> params.put(<span
class="string">"title"</span><span>, </span><span class="string">"中国"</span><span>); </span></span></li><li><span> List<Blog> blogs = blogMapper.dynamicForeach3Test(params); </span></li><li><span> <span
class="keyword">for</span><span> (Blog blog : blogs) </span></span></li><li><span> System.out.println(blog); </span></li><li><span> session.close(); </span></li><li><span>} </span></li></ol></div><pre
name="code" class="java" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="13" title="MyBatis的动态SQL详解" style="display: none;">
@Test
public void dynamicForeach3Test() {
SqlSession session = Util.getSqlSessionFactory().openSession();
BlogMapper blogMapper = session.getMapper(BlogMapper.class);
final List<Integer> ids = new ArrayList<Integer>();
ids.add(1);
ids.add(2);
ids.add(3);
ids.add(6);
ids.add(7);
ids.add(9);
Map<String, Object> params = new HashMap<String, Object>();
params.put("ids", ids);
params.put("title", "中国");
List<Blog> blogs = blogMapper.dynamicForeach3Test(params);
for (Blog blog : blogs)
System.out.println(blog);
session.close();
}
</pre>
</div>
<div> </div>
<div>基础部分可以查看我的另一篇博客：<a href="/blog/1333271">http://haohaoxuexi.iteye.com/blog/1333271</a>
</div>
<div>
<h3>基于3.3.1版本验证的新特性</h3>
</div>
<div> 本文是基于Mybatis 3.0.6版本所写，笔者最近在查看新版Mybatis（3.3.1）时发现其对动态SQL的支持较以前的3.0.6版本的区别不大，基本一致，但笔者还是发现有以下新特性：</div>
<div>1、foreach标签遍历的集合元素类型是Map.Entry类型时，index属性指定的变量代表对应的Map.Entry的key，item属性指定的变量代表对应的Map.Entry的value。此时如果对应的集合是Map.entrySet，则对应的collection属性用collection。foreach在进行遍历的时候如果传入的参数是List类型，则其collection属性的值可以是list或collection，但如果传入的参数是Set类型，则collection属性的值只能用collection。</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%3Cselect%20id%3D%22dynamicForeachTest%22%20resultType%3D%22Blog%22%3E%0A%09%09select%20*%20from%20t_blog%20where%20id%20in%0A%09%09%3C!--%20%E9%81%8D%E5%8E%86%E7%9A%84%E5%AF%B9%E8%B1%A1%E6%98%AFMap.Entry%E6%97%B6%EF%BC%8Cindex%E4%BB%A3%E8%A1%A8%E5%AF%B9%E5%BA%94%E7%9A%84key%EF%BC%8Citem%E4%BB%A3%E8%A1%A8%E5%AF%B9%E5%BA%94%E7%9A%84value%20--%3E%0A%09%09%3Cforeach%20collection%3D%22collection%22%20index%3D%22key%22%20item%3D%22value%22%20open%3D%22(%22%20separator%3D%22%2C%22%20close%3D%22)%22%3E%0A%09%09%09%23%7Bkey%7D%2C%20%23%7Bvalue%7D%0A%09%09%3C%2Fforeach%3E%0A%09%3C%2Fselect%3E"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span class="tag"><</span><span class="tag-name">select</span><span> </span><span class="attribute">id</span><span>=</span><span
class="attribute-value">"dynamicForeachTest"</span><span> </span><span class="attribute">resultType</span><span>=</span><span class="attribute-value">"Blog"</span><span class="tag">></span><span> </span></span></li><li><span> select * from t_blog where id in </span></li><li><span> <span
class="comments"><!-- 遍历的对象是Map.Entry时，index代表对应的key，item代表对应的value --></span><span> </span></span></li><li><span> <span class="tag"><</span><span class="tag-name">foreach</span><span> </span><span
class="attribute">collection</span><span>=</span><span class="attribute-value">"collection"</span><span> </span><span class="attribute">index</span><span>=</span><span class="attribute-value">"key"</span><span> </span><span class="attribute">item</span><span>=</span><span
class="attribute-value">"value"</span><span> </span><span class="attribute">open</span><span>=</span><span class="attribute-value">"("</span><span> </span><span class="attribute">separator</span><span>=</span><span class="attribute-value">","</span><span> </span><span
class="attribute">close</span><span>=</span><span class="attribute-value">")"</span><span class="tag">></span><span> </span></span></li><li><span> #{key}, #{value} </span></li><li><span> <span
class="tag"></</span><span class="tag-name">foreach</span><span class="tag">></span><span> </span></span></li><li><span><span class="tag"></</span><span class="tag-name">select</span><span class="tag">></span><span> </span></span></li></ol></div><pre
name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="14" title="MyBatis的动态SQL详解" style="display: none;">
<select id="dynamicForeachTest" resultType="Blog">
select * from t_blog where id in
<!-- 遍历的对象是Map.Entry时，index代表对应的key，item代表对应的value -->
<foreach collection="collection" index="key" item="value" open="(" separator="," close=")">
#{key}, #{value}
</foreach>
</select></pre>
其对应的接口方法大概是如下这样：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Java代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%20%20%20%20public%20List%3CBlog%3E%20dynamicForeachTest(Set%3CMap.Entry%3CInteger%2C%20Integer%3E%3E%20ids)%3B%0A"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-j"><li><span><span class="keyword">public</span><span> List<Blog> dynamicForeachTest(Set<Map.Entry<Integer, Integer>> ids); </span></span></li></ol></div><pre
name="code" class="java" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="15" title="MyBatis的动态SQL详解" style="display: none;"> public List<Blog> dynamicForeachTest(Set<Map.Entry<Integer, Integer>>
ids);
</pre>
</div>
<div>2、<strong>bind</strong>标签，动态SQL中已经包含了这样一个新的标签，它的功能是在当前OGNL上下文中创建一个变量并绑定一个值。有了它以后我们以前的模糊查询就可以改成这个样子：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%20%20%20%20%3Cselect%20id%3D%22fuzzyQuery%22%20resultType%3D%22Blog%22%20parameterType%3D%22java.lang.String%22%3E%20%20%0A%20%20%20%20%09%3C!--%20bind%E6%A0%87%E7%AD%BE%E7%94%A8%E4%BA%8E%E5%88%9B%E5%BB%BA%E6%96%B0%E7%9A%84%E5%8F%98%E9%87%8F%20--%3E%0A%09%09%3Cbind%20name%3D%22titleLike%22%20value%3D%22'%25'%2B_parameter%2B'%25'%22%2F%3E%0A%20%20%20%20%20%20%20%20select%20*%20from%20t_blog%20where%20title%20like%20%23%7BtitleLike%7D%20%20%0A%20%20%20%20%3C%2Fselect%3E"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span> </span><span class="tag"><</span><span class="tag-name">select</span><span> </span><span
class="attribute">id</span><span>=</span><span class="attribute-value">"fuzzyQuery"</span><span> </span><span class="attribute">resultType</span><span>=</span><span class="attribute-value">"Blog"</span><span> </span><span class="attribute">parameterType</span><span>=</span><span
class="attribute-value">"java.lang.String"</span><span class="tag">></span><span> </span></span></li><li><span> <span class="comments"><!-- bind标签用于创建新的变量 --></span><span> </span></span></li><li><span><span
class="tag"><</span><span class="tag-name">bind</span><span> </span><span class="attribute">name</span><span>=</span><span class="attribute-value">"titleLike"</span><span> </span><span class="attribute">value</span><span>=</span><span class="attribute-value">"'%'+_parameter+'%'"</span><span
class="tag">/></span><span> </span></span></li><li><span> select * from t_blog where title like #{titleLike} </span></li><li><span> <span
class="tag"></</span><span class="tag-name">select</span><span class="tag">></span><span> </span></span></li></ol></div><pre name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#"
pre_index="16" title="MyBatis的动态SQL详解" style="display: none;"> <select id="fuzzyQuery" resultType="Blog" parameterType="java.lang.String">
<!-- bind标签用于创建新的变量 -->
<bind name="titleLike" value="'%'+_parameter+'%'"/>
select * from t_blog where title like #{titleLike}
</select></pre>
</div>
<div> </div>
<div> </div>
<div> </div>
<div> </div>
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<div id="digg_bottom" class="clearfix"><div class="digged"><strong>43</strong> <br>顶</div><div class="digged"><strong>5</strong> <br>踩</div></div>
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<div class="blog_bottom">
<ul>
<li>2012-01-09 12:08</li>
<li>浏览 171212</li>
<li><a href="#comments">评论(13)</a></li>
<li>分类:<a href="http://www.iteye.com/blogs/category/language">编程语言</a></li>
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<h5 class="h3titles">参考知识库</h5>
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<dd><a target="_blank" href="http://lib.csdn.net/base/ai"><img src="http://img.knowledge.csdn.net/upload/base/1479972981201_201.jpg" width="58" height="58" alt=""></a></dd>
<dt>
<a target="_blank" href="http://lib.csdn.net/base/ai" classs="title">人工智能知识库</a>
<span>
<em>4740</em> 关注 <i>|</i> <em>410</em> 收录
</span>
</dt>
</dl>
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<dd><a target="_blank" href="http://lib.csdn.net/base/mongodb"><img src="http://img.knowledge.csdn.net/upload/base/1478676229520_520.jpg" width="58" height="58" alt=""></a></dd>
<dt>
<a target="_blank" href="http://lib.csdn.net/base/mongodb" classs="title">MongoDB知识库</a>
<span>
<em>5620</em> 关注 <i>|</i> <em>336</em> 收录
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<dt>
<a target="_blank" href="http://lib.csdn.net/base/hbase" classs="title">Hbase知识库</a>
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<em>6472</em> 关注 <i>|</i> <em>63</em> 收录
</span>
</dt>
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<dd><a target="_blank" href="http://lib.csdn.net/base/blockchain"><img src="http://img.knowledge.csdn.net/upload/base/1476175342721_721.jpg" width="58" height="58" alt=""></a></dd>
<dt>
<a target="_blank" href="http://lib.csdn.net/base/blockchain" classs="title">区块链知识库</a>
<span>
<em>3121</em> 关注 <i>|</i> <em>108</em> 收录
</span>
</dt>
</dl>
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<div class="blog_comment">
<h5>评论</h5>
<a id="comments" name="comments"></a>
<div id="bc2394641">
<div class="comment_title">
13 楼
<a href="http://563011992.iteye.com" target="_blank" title="吾乃隔壁老王">吾乃隔壁老王</a>
2016-11-07
</div>
<div class="comment_content">3Q，问个问题啊，where里的if里，能不能不加and?</div>
</div>
<div id="bc2383373">
<div class="comment_title">
12 楼
<a href="http://yuang.iteye.com" target="_blank" title="yuang">yuang</a>
2015-12-29
</div>
<div class="comment_content"><table class="bbcode"><tbody><tr><td><img src="<ul></td></tr><tr><td>[*]</td></tr><tr><td></ul>">" target="_blank"><img src="<ul></td></tr><tr><td>[*]</td></tr><tr><td></ul>">"
/><img src="<ul></td></tr><tr><td>[*]</td></tr><tr><td></ul>">" target="_blank"><img src="<ul></td></tr><tr><td>[*]</td></tr><tr><td></ul>">"
wmode="" quality="high" menu="false" pluginspage="http://www.macromedia.com/go/getflashplayer" type="application/x-shockwave-flash" width="200" height="200"></td><td><img src="/images/smiles/icon_surprised.gif"> </td></tr></tbody></table></div>
</div>
<div id="bc2364106">
<div class="comment_title">
11 楼
<a href="http://happymzw.iteye.com" target="_blank" title="happymzw">happymzw</a>
2014-12-04
</div>
<div class="comment_content"><div class="quote_title">Syhenian 写道</div><div class="quote_div"><div class="dp-highlighter" id=""><div class="bar"><div class="tools">Java代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14"
height="15" flashvars="clipboard=%3Cupdate%20id%3D%22dynamicSetTest%22%20parameterType%3D%22Blog%22%3E%20%20%0A%20%20%20%20update%20t_blog%20%20%0A%20%20%20%20%3Cset%3E%20%20%0A%20%20%20%20%20%20%20%20%3Cif%20test%3D%22title%20!%3D%20null%22%3E%20%20%0A%20%20%20%20%20%20%20%20%20%20%20%20title%20%3D%20%23%7Btitle%7D%2C%20%20%0A%20%20%20%20%20%20%20%20%3C%2Fif%3E%20%20%0A%20%20%20%20%20%20%20%20%3Cif%20test%3D%22content%20!%3D%20null%22%3E%20%20%0A%20%20%20%20%20%20%20%20%20%20%20%20content%20%3D%20%23%7Bcontent%7D%2C%20%20%0A%20%20%20%20%20%20%20%20%3C%2Fif%3E%20%20%0A%20%20%20%20%20%20%20%20%3Cif%20test%3D%22owner%20!%3D%20null%22%3E%20%20%0A%20%20%20%20%20%20%20%20%20%20%20%20owner%20%3D%20%23%7Bowner%7D%20%20%0A%20%20%20%20%20%20%20%20%3C%2Fif%3E%20%20%0A%20%20%20%20%3C%2Fset%3E%20%20%0A%20%20%20%20where%20id%20%3D%20%23%7Bid%7D%20%20%0A%3C%2Fupdate%3E%20%20"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-j"><li><span><span><update id=</span><span class="string">"dynamicSetTest"</span><span> parameterType=</span><span
class="string">"Blog"</span><span>> </span></span></li><li><span> update t_blog </span></li><li><span> <set> </span></li><li><span> <<span
class="keyword">if</span><span> test=</span><span class="string">"title != null"</span><span>> </span></span></li><li><span> title = #{title}, </span></li><li><span> </<span
class="keyword">if</span><span>> </span></span></li><li><span> <<span class="keyword">if</span><span> test=</span><span class="string">"content != null"</span><span>> </span></span></li><li><span> content = #{content}, </span></li><li><span> </<span
class="keyword">if</span><span>> </span></span></li><li><span> <<span class="keyword">if</span><span> test=</span><span class="string">"owner != null"</span><span>> </span></span></li><li><span> owner = #{owner} </span></li><li><span> </<span
class="keyword">if</span><span>> </span></span></li><li><span> </set> </span></li><li><span> where id = #{id} </span></li><li><span></update> </span></li></ol></div><pre
name="code" class="java" codeable_id="2364106" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#bc2364106" pre_index="0" title="MyBatis的动态SQL详解" style="display: none;"><update id="dynamicSetTest" parameterType="Blog">
update t_blog
<set>
<if test="title != null">
title = #{title},
</if>
<if test="content != null">
content = #{content},
</if>
<if test="owner != null">
owner = #{owner}
</if>
</set>
where id = #{id}
</update> </pre><br><br>这段可以这样写吗 如果ownner等于null 那语句就是<br><br>update t_blog title= 'title', content='content'<span style="color: red;">,</span> where id='id'<br><br>多了个红色的逗号不会报错？</div><br><br>楼主说了，set会自动处理掉后面的那个逗号的</div>
</div>
<div id="bc2363317">
<div class="comment_title">
10 楼
<a href="http://1106592119.iteye.com" target="_blank" title="简单就是美了">简单就是美了</a>
2014-11-20
</div>
<div class="comment_content"><img src="/images/smiles/icon_idea.gif"> <img src="/images/smiles/icon_idea.gif"> <img src="/images/smiles/icon_idea.gif"> <img src="/images/smiles/icon_idea.gif"> <img src="/images/smiles/icon_idea.gif"> </div>
</div>
<div id="bc2362264">
<div class="comment_title">
9 楼
<a href="http://shiping8000.iteye.com" target="_blank" title="shiping8000">shiping8000</a>
2014-11-06
</div>
<div class="comment_content">写的不错，给赞 <img src="/images/smiles/icon_idea.gif"> </div>
</div>
<div id="bc2357405">
<div class="comment_title">
8 楼
<a href="http://syhenian.iteye.com" target="_blank" title="Syhenian">Syhenian</a>
2014-08-29
</div>
<div class="comment_content"><div class="dp-highlighter" id=""><div class="bar"><div class="tools">Java代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%3Cupdate%20id%3D%22dynamicSetTest%22%20parameterType%3D%22Blog%22%3E%20%20%0A%20%20%20%20update%20t_blog%20%20%0A%20%20%20%20%3Cset%3E%20%20%0A%20%20%20%20%20%20%20%20%3Cif%20test%3D%22title%20!%3D%20null%22%3E%20%20%0A%20%20%20%20%20%20%20%20%20%20%20%20title%20%3D%20%23%7Btitle%7D%2C%20%20%0A%20%20%20%20%20%20%20%20%3C%2Fif%3E%20%20%0A%20%20%20%20%20%20%20%20%3Cif%20test%3D%22content%20!%3D%20null%22%3E%20%20%0A%20%20%20%20%20%20%20%20%20%20%20%20content%20%3D%20%23%7Bcontent%7D%2C%20%20%0A%20%20%20%20%20%20%20%20%3C%2Fif%3E%20%20%0A%20%20%20%20%20%20%20%20%3Cif%20test%3D%22owner%20!%3D%20null%22%3E%20%20%0A%20%20%20%20%20%20%20%20%20%20%20%20owner%20%3D%20%23%7Bowner%7D%20%20%0A%20%20%20%20%20%20%20%20%3C%2Fif%3E%20%20%0A%20%20%20%20%3C%2Fset%3E%20%20%0A%20%20%20%20where%20id%20%3D%20%23%7Bid%7D%20%20%0A%3C%2Fupdate%3E%20%20"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-j"><li><span><span><update id=</span><span class="string">"dynamicSetTest"</span><span> parameterType=</span><span
class="string">"Blog"</span><span>> </span></span></li><li><span> update t_blog </span></li><li><span> <set> </span></li><li><span> <<span
class="keyword">if</span><span> test=</span><span class="string">"title != null"</span><span>> </span></span></li><li><span> title = #{title}, </span></li><li><span> </<span
class="keyword">if</span><span>> </span></span></li><li><span> <<span class="keyword">if</span><span> test=</span><span class="string">"content != null"</span><span>> </span></span></li><li><span> content = #{content}, </span></li><li><span> </<span
class="keyword">if</span><span>> </span></span></li><li><span> <<span class="keyword">if</span><span> test=</span><span class="string">"owner != null"</span><span>> </span></span></li><li><span> owner = #{owner} </span></li><li><span> </<span
class="keyword">if</span><span>> </span></span></li><li><span> </set> </span></li><li><span> where id = #{id} </span></li><li><span></update> </span></li></ol></div><pre
name="code" class="java" codeable_id="2357405" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#bc2357405" pre_index="0" title="MyBatis的动态SQL详解" style="display: none;"><update id="dynamicSetTest" parameterType="Blog">
update t_blog
<set>
<if test="title != null">
title = #{title},
</if>
<if test="content != null">
content = #{content},
</if>
<if test="owner != null">
owner = #{owner}
</if>
</set>
where id = #{id}
</update> </pre><br><br>这段可以这样写吗 如果ownner等于null 那语句就是<br><br>update t_blog title= 'title', content='content'<span style="color: red;">,</span> where id='id'<br><br>多了个红色的逗号不会报错？</div>
</div>
<div id="bc2351761">
<div class="comment_title">
7 楼
<a href="http://slc2006119.iteye.com" target="_blank" title="slc2006119">slc2006119</a>
2014-06-27
</div>
<div class="comment_content">简单，易懂，确实写的不错，赞一个！</div>
</div>
<div id="bc2350561">
<div class="comment_title">
6 楼
<a href="http://schnauzer.iteye.com" target="_blank" title="dmewy">dmewy</a>
2014-06-12
</div>
<div class="comment_content">不错 适合开发初期看</div>
</div>
<div id="bc2349324">
<div class="comment_title">
5 楼
<a href="http://songjianyong.iteye.com" target="_blank" title="宋建勇">宋建勇</a>
2014-05-28
</div>
<div class="comment_content">今天整合MyBatis，帮了大忙了啊！不错啊！<img src="/images/smiles/icon_idea.gif"> </div>
</div>
<div id="bc2348923">
<div class="comment_title">
4 楼
<a href="http://xiaoyaya751.iteye.com" target="_blank" title="18289753290">18289753290</a>
2014-05-23
</div>
<div class="comment_content">不错<img src="/images/smiles/icon_idea.gif"> <img src="/images/smiles/icon_idea.gif"> </div>
</div>
<div id="bc2342280">
<div class="comment_title">
3 楼
<a href="http://lcg19880128.iteye.com" target="_blank" title="lcg19880128">lcg19880128</a>
2014-03-14
</div>
<div class="comment_content"><img src="/images/smiles/icon_idea.gif"> <img src="/images/smiles/icon_idea.gif"> <img src="/images/smiles/icon_idea.gif"> </div>
</div>
<div id="bc2339107">
<div class="comment_title">
2 楼
<a href="http://coffeeboy2012.iteye.com" target="_blank" title="coffeeBoy2012">coffeeBoy2012</a>
2014-02-07
</div>
<div class="comment_content"><img src="/images/smiles/icon_idea.gif"> 很详细</div>
</div>
<div id="bc2332128">
<div class="comment_title">
1 楼
<a href="http://huxiulei.iteye.com" target="_blank" title="huxiulei">huxiulei</a>
2013-11-22
</div>
<div class="comment_content">嗯 写的不错... 简明易懂</div>
</div>
</div>
<div class="blog_comment">
<h5>发表评论</h5>
<p style="text-align:center; margin-top:30px;margin-bottom:0px;"><a href="/login" style="background-color:white;"> <img src="/images/login_icon.png" style="vertical-align:middle; margin-right: 10px;"></a><a href="/login"> 您还没有登录,请您登录后再发表评论 </a></p>
</div>
</div>
<div class="blog_title">
<h3>
<a href="/blog/1338557">MyBatis的动态SQL详解</a>
<em class="actions"> </em>
</h3>
<ul class="blog_categories"><strong>博客分类：</strong> <li><a href="/category/131096">mybatis</a></li> </ul>
<div class="news_tag"><a href="http://www.iteye.com/blogs/tag/MyBatis">MyBatis</a><a href="http://www.iteye.com/blogs/tag/%E5%8A%A8%E6%80%81">动态</a><a href="http://www.iteye.com/blogs/tag/SQL">SQL</a><a href="http://www.iteye.com/blogs/tag/where">where</a><a
href="http://www.iteye.com/blogs/tag/foreach">foreach</a> </div>
</div>
<div id="blog_content" class="blog_content">
<div style="font-size: 14px;" class="iteye-blog-content-contain">
<p><a href="/blog/1333271">http://haohaoxuexi.iteye.com/blog/1333271</a></p>
<p> </p>
<p>MyBatis的动态SQL是基于OGNL表达式的，它可以帮助我们方便的在SQL语句中实现某些逻辑。</p>
<p>MyBatis中用于实现动态SQL的元素主要有：</p>
<p> </p>
<ul>
<li>if</li>
<li>choose（when，otherwise）</li>
<li>trim</li>
<li>where</li>
<li>set</li>
<li>foreach</li>
</ul>
<div>
<strong>if</strong>就是简单的条件判断，利用if语句我们可以实现某些简单的条件选择。先来看如下一个例子：</
4000
div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%3Cselect%20id%3D%22dynamicIfTest%22%20parameterType%3D%22Blog%22%20resultType%3D%22Blog%22%3E%0A%09%09select%20*%20from%20t_blog%20where%201%20%3D%201%0A%09%09%3Cif%20test%3D%22title%20!%3D%20null%22%3E%0A%09%09%09and%20title%20%3D%20%23%7Btitle%7D%0A%09%09%3C%2Fif%3E%0A%09%09%3Cif%20test%3D%22content%20!%3D%20null%22%3E%0A%09%09%09and%20content%20%3D%20%23%7Bcontent%7D%0A%09%09%3C%2Fif%3E%0A%09%09%3Cif%20test%3D%22owner%20!%3D%20null%22%3E%0A%09%09%09and%20owner%20%3D%20%23%7Bowner%7D%0A%09%09%3C%2Fif%3E%0A%09%3C%2Fselect%3E"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span class="tag"><</span><span class="tag-name">select</span><span> </span><span class="attribute">id</span><span>=</span><span
class="attribute-value">"dynamicIfTest"</span><span> </span><span class="attribute">parameterType</span><span>=</span><span class="attribute-value">"Blog"</span><span> </span><span class="attribute">resultType</span><span>=</span><span class="attribute-value">"Blog"</span><span
class="tag">></span><span> </span></span></li><li><span> select * from t_blog where <span class="attribute">1</span><span class="attribute-value">1</span><span> = 1 </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"title != null"</span><span class="tag">></span><span> </span></span></li><li><span> and <span
class="attribute">title</span><span> = #{title} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"content != null"</span><span class="tag">></span><span> </span></span></li><li><span> and <span
class="attribute">content</span><span> = #{content} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"owner != null"</span><span class="tag">></span><span> </span></span></li><li><span> and <span
class="attribute">owner</span><span> = #{owner} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span><span
class="tag"></</span><span class="tag-name">select</span><span class="tag">></span><span> </span></span></li></ol></div><pre name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#"
pre_index="0" title="MyBatis的动态SQL详解" style="display: none;">
<select id="dynamicIfTest" parameterType="Blog" resultType="Blog">
select * from t_blog where 1 = 1
<if test="title != null">
and title = #{title}
</if>
<if test="content != null">
and content = #{content}
</if>
<if test="owner != null">
and owner = #{owner}
</if>
</select></pre>
</div>
<div>这条语句的意思非常简单，如果你提供了title参数，那么就要满足title=#{title}，同样如果你提供了Content和Owner的时候，它们也需要满足相应的条件，之后就是返回满足这些条件的所有Blog，这是非常有用的一个功能，以往我们使用其他类型框架或者直接使用JDBC的时候， 如果我们要达到同样的选择效果的时候，我们就需要拼SQL语句，这是极其麻烦的，比起来，上述的动态SQL就要简单多了。</div>
<div> </div>
<div>
<strong>choose</strong>元素的作用就相当于JAVA中的switch语句，基本上跟JSTL中的choose的作用和用法是一样的，通常都是与when和otherwise搭配的。看如下一个例子：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%3Cselect%20id%3D%22dynamicChooseTest%22%20parameterType%3D%22Blog%22%20resultType%3D%22Blog%22%3E%0A%09%09select%20*%20from%20t_blog%20where%201%20%3D%201%20%0A%09%09%3Cchoose%3E%0A%09%09%09%3Cwhen%20test%3D%22title%20!%3D%20null%22%3E%0A%09%09%09%09and%20title%20%3D%20%23%7Btitle%7D%0A%09%09%09%3C%2Fwhen%3E%0A%09%09%09%3Cwhen%20test%3D%22content%20!%3D%20null%22%3E%0A%09%09%09%09and%20content%20%3D%20%23%7Bcontent%7D%0A%09%09%09%3C%2Fwhen%3E%0A%09%09%09%3Cotherwise%3E%0A%09%09%09%09and%20owner%20%3D%20%22owner1%22%0A%09%09%09%3C%2Fotherwise%3E%0A%09%09%3C%2Fchoose%3E%0A%09%3C%2Fselect%3E"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span class="tag"><</span><span class="tag-name">select</span><span> </span><span class="attribute">id</span><span>=</span><span
class="attribute-value">"dynamicChooseTest"</span><span> </span><span class="attribute">parameterType</span><span>=</span><span class="attribute-value">"Blog"</span><span> </span><span class="attribute">resultType</span><span>=</span><span class="attribute-value">"Blog"</span><span
class="tag">></span><span> </span></span></li><li><span> select * from t_blog where <span class="attribute">1</span><span class="attribute-value">1</span><span> = 1 </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">choose</span><span class="tag">></span><span> </span></span></li><li><span> <span class="tag"><</span><span class="tag-name">when</span><span> </span><span
class="attribute">test</span><span>=</span><span class="attribute-value">"title != null"</span><span class="tag">></span><span> </span></span></li><li><span> and <span
class="attribute">title</span><span> = #{title} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">when</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">when</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"content != null"</span><span class="tag">></span><span> </span></span></li><li><span> and <span
class="attribute">content</span><span> = #{content} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">when</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">otherwise</span><span class="tag">></span><span> </span></span></li><li><span> and <span class="attribute">owner</span><span> = </span><span
class="attribute-value">"owner1"</span><span> </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">otherwise</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"></</span><span class="tag-name">choose</span><span class="tag">></span><span> </span></span></li><li><span><span class="tag"></</span><span class="tag-name">select</span><span class="tag">></span><span> </span></span></li></ol></div><pre
name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="1" title="MyBatis的动态SQL详解" style="display: none;">
<select id="dynamicChooseTest" parameterType="Blog" resultType="Blog">
select * from t_blog where 1 = 1
<choose>
<when test="title != null">
and title = #{title}
</when>
<when test="content != null">
and content = #{content}
</when>
<otherwise>
and owner = "owner1"
</otherwise>
</choose>
</select></pre>
</div>
<div>when元素表示当when中的条件满足的时候就输出其中的内容，跟JAVA中的switch效果差不多的是按照条件的顺序，当when中有条件满足的时候，就会跳出choose，即所有的when和otherwise条件中，只有一个会输出，当所有的我很条件都不满足的时候就输出otherwise中的内容。所以上述语句的意思非常简单， 当title!=null的时候就输出and titlte = #{title}，不再往下判断条件，当title为空且content!=null的时候就输出and content =
#{content}，当所有条件都不满足的时候就输出otherwise中的内容。</div>
<div> </div>
<div>
<strong>where</strong>语句的作用主要是简化SQL语句中where中的条件判断的，先看一个例子，再解释一下where的好处。</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%3Cselect%20id%3D%22dynamicWhereTest%22%
20000
20parameterType%3D%22Blog%22%20resultType%3D%22Blog%22%3E%0A%09%09select%20*%20from%20t_blog%20%0A%09%09%3Cwhere%3E%0A%09%09%09%3Cif%20test%3D%22title%20!%3D%20null%22%3E%0A%09%09%09%09title%20%3D%20%23%7Btitle%7D%0A%09%09%09%3C%2Fif%3E%0A%09%09%09%3Cif%20test%3D%22content%20!%3D%20null%22%3E%0A%09%09%09%09and%20content%20%3D%20%23%7Bcontent%7D%0A%09%09%09%3C%2Fif%3E%0A%09%09%09%3Cif%20test%3D%22owner%20!%3D%20null%22%3E%0A%09%09%09%09and%20owner%20%3D%20%23%7Bowner%7D%0A%09%09%09%3C%2Fif%3E%0A%09%09%3C%2Fwhere%3E%0A%09%3C%2Fselect%3E%0A"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span class="tag"><</span><span class="tag-name">select</span><span> </span><span class="attribute">id</span><span>=</span><span
class="attribute-value">"dynamicWhereTest"</span><span> </span><span class="attribute">parameterType</span><span>=</span><span class="attribute-value">"Blog"</span><span> </span><span class="attribute">resultType</span><span>=</span><span class="attribute-value">"Blog"</span><span
class="tag">></span><span> </span></span></li><li><span> select * from t_blog </span></li><li><span> <span class="tag"><</span><span class="tag-name">where</span><span
class="tag">></span><span> </span></span></li><li><span> <span class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"title != null"</span><span
class="tag">></span><span> </span></span></li><li><span> <span class="attribute">title</span><span> = #{title} </span></span></li><li><span> <span
class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span class="tag"><</span><span class="tag-name">if</span><span> </span><span
class="attribute">test</span><span>=</span><span class="attribute-value">"content != null"</span><span class="tag">></span><span> </span></span></li><li><span> and <span
class="attribute">content</span><span> = #{content} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"owner != null"</span><span class="tag">></span><span> </span></span></li><li><span> and <span
class="attribute">owner</span><span> = #{owner} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"></</span><span class="tag-name">where</span><span class="tag">></span><span> </span></span></li><li><span><span class="tag"></</span><span class="tag-name">select</span><span class="tag">></span><span> </span></span></li></ol></div><pre
name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="2" title="MyBatis的动态SQL详解" style="display: none;">
<select id="dynamicWhereTest" parameterType="Blog" resultType="Blog">
select * from t_blog
<where>
<if test="title != null">
title = #{title}
</if>
<if test="content != null">
and content = #{content}
</if>
<if test="owner != null">
and owner = #{owner}
</if>
</where>
</select>
</pre>
</div>
<div> where元素的作用是会在写入where元素的地方输出一个where，另外一个好处是你不需要考虑where元素里面的条件输出是什么样子的，MyBatis会智能的帮你处理，如果所有的条件都不满足那么MyBatis就会查出所有的记录，如果输出后是and 开头的，MyBatis会把第一个and忽略，当然如果是or开头的，MyBatis也会把它忽略；此外，在where元素中你不需要考虑空格的问题，MyBatis会智能的帮你加上。像上述例子中，如果title=null， 而content != null，那么输出的整个语句会是select
* from t_blog where content = #{content}，而不是select * from t_blog where and content = #{content}，因为MyBatis会智能的把首个and 或 or 给忽略。</div>
<div> </div>
<div>
<strong>trim</strong>元素的主要功能是可以在自己包含的内容前加上某些前缀，也可以在其后加上某些后缀，与之对应的属性是prefix和suffix；可以把包含内容的首部某些内容覆盖，即忽略，也可以把尾部的某些内容覆盖，对应的属性是prefixOverrides和suffixOverrides；正因为trim有这样的功能，所以我们也可以非常简单的利用trim来代替where元素的功能，示例代码如下：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%3Cselect%20id%3D%22dynamicTrimTest%22%20parameterType%3D%22Blog%22%20resultType%3D%22Blog%22%3E%0A%09%09select%20*%20from%20t_blog%20%0A%09%09%3Ctrim%20prefix%3D%22where%22%20prefixOverrides%3D%22and%20%7Cor%22%3E%0A%09%09%09%3Cif%20test%3D%22title%20!%3D%20null%22%3E%0A%09%09%09%09title%20%3D%20%23%7Btitle%7D%0A%09%09%09%3C%2Fif%3E%0A%09%09%09%3Cif%20test%3D%22content%20!%3D%20null%22%3E%0A%09%09%09%09and%20content%20%3D%20%23%7Bcontent%7D%0A%09%09%09%3C%2Fif%3E%0A%09%09%09%3Cif%20test%3D%22owner%20!%3D%20null%22%3E%0A%09%09%09%09or%20owner%20%3D%20%23%7Bowner%7D%0A%09%09%09%3C%2Fif%3E%0A%09%09%3C%2Ftrim%3E%0A%09%3C%2Fselect%3E"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span class="tag"><</span><span class="tag-name">select</span><span> </span><span class="attribute">id</span><span>=</span><span
class="attribute-value">"dynamicTrimTest"</span><span> </span><span class="attribute">parameterType</span><span>=</span><span class="attribute-value">"Blog"</span><span> </span><span class="attribute">resultType</span><span>=</span><span class="attribute-value">"Blog"</span><span
class="tag">></span><span> </span></span></li><li><span> select * from t_blog </span></li><li><span> <span class="tag"><</span><span class="tag-name">trim</span><span> </span><span
class="attribute">prefix</span><span>=</span><span class="attribute-value">"where"</span><span> </span><span class="attribute">prefixOverrides</span><span>=</span><span class="attribute-value">"and |or"</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"title != null"</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="attribute">title</span><span> = #{title} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"content != null"</span><span class="tag">></span><span> </span></span></li><li><span> and <span
class="attribute">content</span><span> = #{content} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"owner != null"</span><span class="tag">></span><span> </span></span></li><li><span> or <span
class="attribute">owner</span><span> = #{owner} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"></</span><span class="tag-name">trim</span><span class="tag">></span><span> </span></span></li><li><span><span class="tag"></</span><span class="tag-name">select</span><span class="tag">></span><span> </span></span></li></ol></div><pre
name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="3" title="MyBatis的动态SQL详解" style="display: none;">
<select id="dynamicTrimTest" parameterType="Blog" resultType="Blog">
select * from t_blog
<trim prefix="where" prefixOverrides="and |or">
<if test="title != null">
title = #{title}
</if>
<if test="content != null">
and content = #{content}
</if>
<if test="owner != null">
or owner = #{owner}
</if>
</trim>
</select></pre>
</div>
<div> </div>
<div>
<strong>set</strong>元素主要是用在更新操作的时候，它的主要功能和where元素其实是差不多的，主要是在包含的语句前输出一个set，然后如果包含的语句是以逗号结束的话将会把该逗号忽略，如果set包含的内容为空的话则会出错。有了set元素我们就可以动态的更新那些修改了的字段。下面是一段示例代码：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%3Cupdate%20id%3D%22dynamicSetTest%22%20parameterType%3D%22Blog%22%3E%0A%09%09update%20t_blog%0A%09%09%3Cset%3E%0A%09%09%09%3Cif%20test%3D%22title%20!%3D%20null%22%3E%0A%09%09%09%09title%20%3D%20%23%7Btitle%7D%2C%0A%09%09%09%3C%2Fif%3E%0A%09%09%09%3Cif%20test%3D%22content%20!%3D%20null%22%3E%0A%09%09%09%09content%20%3D%20%23%7Bcontent%7D%2C%0A%09%09%09%3C%2Fif%3E%0A%09%09%09%3Cif%20test%3D%22owner%20!%3D%20null%22%3E%0A%09%09%09%09owner%20%3D%20%23%7Bowner%7D%0A%09%09%09%3C%2Fif%3E%0A%09%09%3C%2Fset%3E%0A%09%09where%20id%20%3D%20%23%7Bid%7D%0A%09%3C%2Fupdate%3E"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span class="tag"><</span><span class="tag-name">update</span><span> </span><span class="attribute">id</span><span>=</span><span
class="attribute-value">"dynamicSetTest"</span><span> </span><span class="attribute">parameterType</span><span>=</span><span class="attribute-value">"Blog"</span><span class="tag">></span><span> </span></span></li><li><span> update t_blog </span></li><li><span> <span
class="tag"><</span><span class="tag-name">set</span><span class="tag">></span><span> </span></span></li><li><span> <span class="tag"><</span><span class="tag-name">if</span><span> </span><span
class="attribute">test</span><span>=</span><span class="attribute-value">"title != null"</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="attribute">title</span><span> = #{title}, </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"content != null"</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="attribute">content</span><span> = #{content}, </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"><</span><span class="tag-name">if</span><span> </span><span class="attribute">test</span><span>=</span><span class="attribute-value">"owner != null"</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="attribute">owner</span><span> = #{owner} </span></span></li><li><span> <span class="tag"></</span><span class="tag-name">if</span><span class="tag">></span><span> </span></span></li><li><span> <span
class="tag"></</span><span class="tag-name">set</span><span class="tag">></span><span> </span></span></li><li><span> where <span class="attribute">id</span><span> = #{id} </span></span></li><li><span><span
class="tag"></</span><span class="tag-name">update</span><span class="tag">></span><span> </span></span></li></ol></div><pre name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#"
pre_index="4" title="MyBatis的动态SQL详解" style="display: none;">
<update id="dynamicSetTest" parameterType="Blog">
update t_blog
<set>
<if test="title != null">
title = #{title},
</if>
<if test="content != null">
content = #{content},
</if>
<if test="owner != null">
owner = #{owner}
</if>
</set>
where id = #{id}
</update></pre>
</div>
<div> 上述示例代码中，如果set中一个条件都不满足，即set中包含的内容为空的时候就会报错。</div>
<div> </div>
<div>
<strong>foreach</strong>的主要用在构建in条件中，它可以在SQL语句中进行迭代一个集合。foreach元素的属性主要有item，index，collection，open，separator，close。item表示集合中每一个元素进行迭代时的别名，index指定一个名字，用于表示在迭代过程中，每次迭代到的位置，open表示该语句以什么开始，separator表示在每次进行迭代之间以什么符号作为分隔符，close表示以什么结束，在使用foreach的时候最关键的也是最容易出错的就是collection属性，该属性是必须指定的，但是在不同情况下，该属性的值是不一样的，主要有一下3种情况：</div>
<div>
<ol>
<li>如果传入的是单参数且参数类型是一个List的时候，collection属性值为list</li>
<li>如果传入的是单参数且参数类型是一个array数组的时候，collection的属性值为array</li>
<li>如果传入的参数是多个的时候，我们就需要把它们封装成一个Map了，<strong>当然单参数也可以封装成map</strong>，实际上如果你在传入参数的时候，在MyBatis里面也是会把它封装成一个Map的，map的key就是参数名，所以这个时候collection属性值就是传入的List或array对象在自己封装的map里面的key</li>
</ol>
<div>下面分别来看看上述三种情况的示例代码：</div>
<div>1.单参数List的类型：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%3Cselect%20id%3D%22dynamicForeachTest%22%20resultType%3D%22Blog%22%3E%0A%09%09select%20*%20from%20t_blog%20where%20id%20in%0A%09%09%3Cforeach%20collection%3D%22list%22%20index%3D%22index%22%20item%3D%22item%22%20open%3D%22(%22%20separator%3D%22%2C%22%20close%3D%22)%22%3E%0A%09%09%09%23%7Bitem%7D%0A%09%09%3C%2Fforeach%3E%0A%09%3C%2Fselect%3E"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span class="tag"><</span><span class="tag-name">select</span><span> </span><span class="attribute">id</span><span>=</span><span
class="attribute-value">"dynamicForeachTest"</span><span> </span><span class="attribute">resultType</span><span>=</span><span class="attribute-value">"Blog"</span><span class="tag">></span><span> </span></span></li><li><span> select * from t_blog where id in </span></li><li><span> <span
class="tag"><</span><span class="tag-name">foreach</span><span> </span><span class="attribute">collection</span><span>=</span><span class="attribute-value">"list"</span><span> </span><span class="attribute">index</span><span>=</span><span class="attribute-value">"index"</span><span> </span><span
class="attribute">item</span><span>=</span><span class="attribute-value">"item"</span><span> </span><span class="attribute">open</span><span>=</span><span class="attribute-value">"("</span><span> </span><span class="attribute">separator</span><span>=</span><span
class="attribute-value">","</span><span> </span><span class="attribute">close</span><span>=</span><span class="attribute-value">")"</span><span class="tag">></span><span> </span></span></li><li><span> #{item} </span></li><li><span> <span
class="tag"></</span><span class="tag-name">foreach</span><span class="tag">></span><span> </span></span></li><li><span><span class="tag"></</span><span class="tag-name">select</span><span class="tag">></span><span> </span></span></li></ol></div><pre
name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="5" title="MyBatis的动态SQL详解" style="display: none;">
<select id="dynamicForeachTest" resultType="Blog">
select * from t_blog where id in
<foreach collection="list" index="index" item="item" open="(" separator="," close=")">
#{item}
</foreach>
</select></pre>
</div>
<div> 上述collection的值为list，对应的Mapper是这样的</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Java代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=public%20List%3CBlog%3E%20dynamicForeachTest(List%3CInteger%3E%20ids)%3B"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-j"><li><span><span class="keyword">public</span><span> List<Blog> dynamicForeachTest(List<Integer> ids); </span></span></li></ol></div><pre
name="code" class="java" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="6" title="MyBatis的动态SQL详解" style="display: none;">public List<Blog> dynamicForeachTest(List<Integer> ids);</pre>
</div>
<div> 测试代码：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Java代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%40Test%0A%09public%20void%20dynamicForeachTest()%20%7B%0A%09%09SqlSession%20session%20%3D%20Util.getSqlSessionFactory().openSession()%3B%0A%09%09BlogMapper%20blogMapper%20%3D%20session.getMapper(BlogMapper.class)%3B%0A%09%09List%3CInteger%3E%20ids%20%3D%20new%20ArrayList%3CInteger%3E()%3B%0A%09%09ids.add(1)%3B%0A%09%09ids.add(3)%3B%0A%09%09ids.add(6)%3B%0A%09%09List%3CBlog%3E%20blogs%20%3D%20blogMapper.dynamicForeachTest(ids)%3B%0A%09%09for%20(Blog%20blog%20%3A%20blogs)%0A%09%09%09System.out.println(blog)%3B%0A%09%09session.close()%3B%0A%09%7D"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-j"><li><span><span class="annotation">@Test</span><span> </span></span></li><li><span><span class="keyword">public</span><span> </span><span
class="keyword">void</span><span> dynamicForeachTest() { </span></span></li><li><span> SqlSession session = Util.getSqlSessionFactory().openSession(); </span></li><li><span> BlogMapper blogMapper = session.getMapper(BlogMapper.<span
class="keyword">class</span><span>); </span></span></li><li><span> List<Integer> ids = <span class="keyword">new</span><span> ArrayList<Integer>(); </span></span></li><li><span> ids.add(<span
class="number">1</span><span>); </span></span></li><li><span> ids.add(<span class="number">3</span><span>); </span></span></li><li><span> ids.add(<span class="number">6</span><span>); </span></span></li><li><span> List<Blog> blogs = blogMapper.dynamicForeachTest(ids); </span></li><li><span> <span
class="keyword">for</span><span> (Blog blog : blogs) </span></span></li><li><span> System.out.println(blog); </span></li><li><span> session.close(); </span></li><li><span>} </span></li></ol></div><pre
name="code" class="java" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="7" title="MyBatis的动态SQL详解" style="display: none;">
@Test
public void dynamicForeachTest() {
SqlSession session = Util.getSqlSessionFactory().openSession();
BlogMapper blogMapper = session.getMapper(BlogMapper.class);
List<Integer> ids = new ArrayList<Integer>();
ids.add(1);
ids.add(3);
ids.add(6);
List<Blog> blogs = blogMapper.dynamicForeachTest(ids);
for (Blog blog : blogs)
System.out.println(blog);
session.close();
}</pre>
</div>
<div> </div>
<div>2.单参数array数组的类型：</div>
</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%3Cselect%20id%3D%22dynamicForeach2Test%22%20resultType%3D%22Blog%22%3E%0A%09%09select%20*%20from%20t_blog%20where%20id%20in%0A%09%09%3Cforeach%20collection%3D%22array%22%20index%3D%22index%22%20item%3D%22item%22%20open%3D%22(%22%20separator%3D%22%2C%22%20close%3D%22)%22%3E%0A%09%09%09%23%7Bitem%7D%0A%09%09%3C%2Fforeach%3E%0A%09%3C%2Fselect%3E%0A"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span class="tag"><</span><span class="tag-name">select</span><span> </span><span class="attribute">id</span><span>=</span><span
class="attribute-value">"dynamicForeach2Test"</span><span> </span><span class="attribute">resultType</span><span>=</span><span class="attribute-value">"Blog"</span><span class="tag">></span><span> </span></span></li><li><span> select * from t_blog where id in </span></li><li><span> <span
class="tag"><</span><span class="tag-name">foreach</span><span> </span><span class="attribute">collection</span><span>=</span><span class="attribute-value">"array"</span><span> </span><span class="attribute">index</span><span>=</span><span class="attribute-value">"index"</span><span> </span><span
class="attribute">item</span><span>=</span><span class="attribute-value">"item"</span><span> </span><span class="attribute">open</span><span>=</span><span class="attribute-value">"("</span><span> </span><span class="attribute">separator</span><span>=</span><span
class="attribute-value">","</span><span> </span><span class="attribute">close</span><span>=</span><span class="attribute-value">")"</span><span class="tag">></span><span> </span></span></li><li><span> #{item} </span></li><li><span> <span
class="tag"></</span><span class="tag-name">foreach</span><span class="tag">></span><span> </span></span></li><li><span><span class="tag"></</span><span class="tag-name">select</span><span class="tag">></span><span> </span></span></li></ol></div><pre
name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="8" title="MyBatis的动态SQL详解" style="display: none;">
<select id="dynamicForeach2Test" resultType="Blog">
select * from t_blog where id in
<foreach collection="array" index="index" item="item" open="(" separator="," close=")">
#{item}
</foreach>
</select>
</pre>
</div>
<div> 上述collection为array，对应的Mapper代码：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Java代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=public%20List%3CBlog%3E%20dynamicForeach2Test(int%5B%5D%20ids)%3B"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-j"><li><span><span class="keyword">public</span><span> List<Blog> dynamicForeach2Test(</span><span
class="keyword">int</span><span>[] ids); </span></span></li></ol></div><pre name="code" class="java" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="9" title="MyBatis的动态SQL详解" style="display:
none;">public List<Blog> dynamicForeach2Test(int[] ids);</pre>
</div>
<div> 对应的测试代码：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Java代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%40Test%0A%09public%20void%20dynamicForeach2Test()%20%7B%0A%09%09SqlSession%20session%20%3D%20Util.getSqlSessionFactory().openSession()%3B%0A%09%09BlogMapper%20blogMapper%20%3D%20session.getMapper(BlogMapper.class)%3B%0A%09%09int%5B%5D%20ids%20%3D%20new%20int%5B%5D%20%7B1%2C3%2C6%2C9%7D%3B%0A%09%09List%3CBlog%3E%20blogs%20%3D%20blogMapper.dynamicForeach2Test(ids)%3B%0A%09%09for%20(Blog%20blog%20%3A%20blogs)%0A%09%09%09System.out.println(blog)%3B%0A%09%09session.close()%3B%0A%09%7D"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-j"><li><span><span class="annotation">@Test</span><span> </span></span></li><li><span><span class="keyword">public</span><span> </span><span
class="keyword">void</span><span> dynamicForeach2Test() { </span></span></li><li><span> SqlSession session = Util.getSqlSessionFactory().openSession(); </span></li><li><span> BlogMapper blogMapper = session.getMapper(BlogMapper.<span
class="keyword">class</span><span>); </span></span></li><li><span> <span class="keyword">int</span><span>[] ids = </span><span class="keyword">new</span><span> </span><span class="keyword">int</span><span>[] {</span><span
class="number">1</span><span>,</span><span class="number">3</span><span>,</span><span class="number">6</span><span>,</span><span class="number">9</span><span>}; </span></span></li><li><span> List<Blog> blogs = blogMapper.dynamicForeach2Test(ids); </span></li><li><span> <span
class="keyword">for</span><span> (Blog blog : blogs) </span></span></li><li><span> System.out.println(blog); </span></li><li><span> session.close(); </span></li><li><span>} </span></li></ol></div><pre
name="code" class="java" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="10" title="MyBatis的动态SQL详解" style="display: none;">
@Test
public void dynamicForeach2Test() {
SqlSession session = Util.getSqlSessionFactory().openSession();
BlogMapper blogMapper = session.getMapper(BlogMapper.class);
int[] ids = new int[] {1,3,6,9};
List<Blog> blogs = blogMapper.dynamicForeach2Test(ids);
for (Blog blog : blogs)
System.out.println(blog);
session.close();
}</pre>
</div>
<div> </div>
<div>3.自己把参数封装成Map的类型</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%3Cselect%20id%3D%22dynamicForeach3Test%22%20resultType%3D%22Blog%22%3E%0A%09%09select%20*%20from%20t_blog%20where%20title%20like%20%22%25%22%23%7Btitle%7D%22%25%22%20and%20id%20in%0A%09%09%3Cforeach%20collection%3D%22ids%22%20index%3D%22index%22%20item%3D%22item%22%20open%3D%22(%22%20separator%3D%22%2C%22%20close%3D%22)%22%3E%0A%09%09%09%23%7Bitem%7D%0A%09%09%3C%2Fforeach%3E%0A%09%3C%2Fselect%3E"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span class="tag"><</span><span class="tag-name">select</span><span> </span><span class="attribute">id</span><span>=</span><span
class="attribute-value">"dynamicForeach3Test"</span><span> </span><span class="attribute">resultType</span><span>=</span><span class="attribute-value">"Blog"</span><span class="tag">></span><span> </span></span></li><li><span> select * from t_blog where title like "%"#{title}"%" and id in </span></li><li><span> <span
class="tag"><</span><span class="tag-name">foreach</span><span> </span><span class="attribute">collection</span><span>=</span><span class="attribute-value">"ids"</span><span> </span><span class="attribute">index</span><span>=</span><span class="attribute-value">"index"</span><span> </span><span
class="attribute">item</span><span>=</span><span class="attribute-value">"item"</span><span> </span><span class="attribute">open</span><span>=</span><span class="attribute-value">"("</span><span> </span><span class="attribute">separator</span><span>=</span><span
class="attribute-value">","</span><span> </span><span class="attribute">close</span><span>=</span><span class="attribute-value">")"</span><span class="tag">></span><span> </span></span></li><li><span> #{item} </span></li><li><span> <span
class="tag"></</span><span class="tag-name">foreach</span><span class="tag">></span><span> </span></span></li><li><span><span class="tag"></</span><span class="tag-name">select</span><span class="tag">></span><span> </span></span></li></ol></div><pre
name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="11" title="MyBatis的动态SQL详解" style="display: none;">
<select id="dynamicForeach3Test" resultType="Blog">
select * from t_blog where title like "%"#{title}"%" and id in
<foreach collection="ids" index="index" item="item" open="(" separator="," close=")">
#{item}
</foreach>
</select></pre>
</div>
<div>上述collection的值为ids，是传入的参数Map的key，对应的Mapper代码：</div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Java代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=public%20List%3CBlog%3E%20dynamicForeach3Test(Map%3CString%2C%20Object%3E%20params)%3B"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-j"><li><span><span class="keyword">public</span><span> List<Blog> dynamicForeach3Test(Map<String, Object> params); </span></span></li></ol></div><pre
name="code" class="java" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="12" title="MyBatis的动态SQL详解" style="display: none;">public List<Blog> dynamicForeach3Test(Map<String, Object> params);</pre>
<div> 对应测试代码：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Java代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%40Test%0A%09public%20void%20dynamicForeach3Test()%20%7B%0A%09%09SqlSession%20session%20%3D%20Util.getSqlSessionFactory().openSession()%3B%0A%09%09BlogMapper%20blogMapper%20%3D%20session.getMapper(BlogMapper.class)%3B%0A%09%09final%20List%3CInteger%3E%20ids%20%3D%20new%20ArrayList%3CInteger%3E()%3B%0A%09%09ids.add(1)%3B%0A%09%09ids.add(2)%3B%0A%09%09ids.add(3)%3B%0A%09%09ids.add(6)%3B%0A%09%09ids.add(7)%3B%0A%09%09ids.add(9)%3B%0A%09%09Map%3CString%2C%20Object%3E%20params%20%3D%20new%20HashMap%3CString%2C%20Object%3E()%3B%0A%09%09params.put(%22ids%22%2C%20ids)%3B%0A%09%09params.put(%22title%22%2C%20%22%E4%B8%AD%E5%9B%BD%22)%3B%0A%09%09List%3CBlog%3E%20blogs%20%3D%20blogMapper.dynamicForeach3Test(params)%3B%0A%09%09for%20(Blog%20blog%20%3A%20blogs)%0A%09%09%09System.out.println(blog)%3B%0A%09%09session.close()%3B%0A%09%7D%0A"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-j"><li><span><span class="annotation">@Test</span><span> </span></span></li><li><span><span class="keyword">public</span><span> </span><span
class="keyword">void</span><span> dynamicForeach3Test() { </span></span></li><li><span> SqlSession session = Util.getSqlSessionFactory().openSession(); </span></li><li><span> BlogMapper blogMapper = session.getMapper(BlogMapper.<span
class="keyword">class</span><span>); </span></span></li><li><span> <span class="keyword">final</span><span> List<Integer> ids = </span><span class="keyword">new</span><span> ArrayList<Integer>(); </span></span></li><li><span> ids.add(<span
class="number">1</span><span>); </span></span></li><li><span> ids.add(<span class="number">2</span><span>); </span></span></li><li><span> ids.add(<span class="number">3</span><span>); </span></span></li><li><span> ids.add(<span
class="number">6</span><span>); </span></span></li><li><span> ids.add(<span class="number">7</span><span>); </span></span></li><li><span> ids.add(<span class="number">9</span><span>); </span></span></li><li><span> Map<String, Object> params = <span
class="keyword">new</span><span> HashMap<String, Object>(); </span></span></li><li><span> params.put(<span class="string">"ids"</span><span>, ids); </span></span></li><li><span> params.put(<span
class="string">"title"</span><span>, </span><span class="string">"中国"</span><span>); </span></span></li><li><span> List<Blog> blogs = blogMapper.dynamicForeach3Test(params); </span></li><li><span> <span
class="keyword">for</span><span> (Blog blog : blogs) </span></span></li><li><span> System.out.println(blog); </span></li><li><span> session.close(); </span></li><li><span>} </span></li></ol></div><pre
name="code" class="java" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="13" title="MyBatis的动态SQL详解" style="display: none;">
@Test
public void dynamicForeach3Test() {
SqlSession session = Util.getSqlSessionFactory().openSession();
BlogMapper blogMapper = session.getMapper(BlogMapper.class);
final List<Integer> ids = new ArrayList<Integer>();
ids.add(1);
ids.add(2);
ids.add(3);
ids.add(6);
ids.add(7);
ids.add(9);
Map<String, Object> params = new HashMap<String, Object>();
params.put("ids", ids);
params.put("title", "中国");
List<Blog> blogs = blogMapper.dynamicForeach3Test(params);
for (Blog blog : blogs)
System.out.println(blog);
session.close();
}
</pre>
</div>
<div> </div>
<div>基础部分可以查看我的另一篇博客：<a href="/blog/1333271">http://haohaoxuexi.iteye.com/blog/1333271</a>
</div>
<div>
<h3>基于3.3.1版本验证的新特性</h3>
</div>
<div> 本文是基于Mybatis 3.0.6版本所写，笔者最近在查看新版Mybatis（3.3.1）时发现其对动态SQL的支持较以前的3.0.6版本的区别不大，基本一致，但笔者还是发现有以下新特性：</div>
<div>1、foreach标签遍历的集合元素类型是Map.Entry类型时，index属性指定的变量代表对应的Map.Entry的key，item属性指定的变量代表对应的Map.Entry的value。此时如果对应的集合是Map.entrySet，则对应的collection属性用collection。foreach在进行遍历的时候如果传入的参数是List类型，则其collection属性的值可以是list或collection，但如果传入的参数是Set类型，则collection属性的值只能用collection。</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%09%3Cselect%20id%3D%22dynamicForeachTest%22%20resultType%3D%22Blog%22%3E%0A%09%09select%20*%20from%20t_blog%20where%20id%20in%0A%09%09%3C!--%20%E9%81%8D%E5%8E%86%E7%9A%84%E5%AF%B9%E8%B1%A1%E6%98%AFMap.Entry%E6%97%B6%EF%BC%8Cindex%E4%BB%A3%E8%A1%A8%E5%AF%B9%E5%BA%94%E7%9A%84key%EF%BC%8Citem%E4%BB%A3%E8%A1%A8%E5%AF%B9%E5%BA%94%E7%9A%84value%20--%3E%0A%09%09%3Cforeach%20collection%3D%22collection%22%20index%3D%22key%22%20item%3D%22value%22%20open%3D%22(%22%20separator%3D%22%2C%22%20close%3D%22)%22%3E%0A%09%09%09%23%7Bkey%7D%2C%20%23%7Bvalue%7D%0A%09%09%3C%2Fforeach%3E%0A%09%3C%2Fselect%3E"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span class="tag"><</span><span class="tag-name">select</span><span> </span><span class="attribute">id</span><span>=</span><span
class="attribute-value">"dynamicForeachTest"</span><span> </span><span class="attribute">resultType</span><span>=</span><span class="attribute-value">"Blog"</span><span class="tag">></span><span> </span></span></li><li><span> select * from t_blog where id in </span></li><li><span> <span
class="comments"><!-- 遍历的对象是Map.Entry时，index代表对应的key，item代表对应的value --></span><span> </span></span></li><li><span> <span class="tag"><</span><span class="tag-name">foreach</span><span> </span><span
class="attribute">collection</span><span>=</span><span class="attribute-value">"collection"</span><span> </span><span class="attribute">index</span><span>=</span><span class="attribute-value">"key"</span><span> </span><span class="attribute">item</span><span>=</span><span
class="attribute-value">"value"</span><span> </span><span class="attribute">open</span><span>=</span><span class="attribute-value">"("</span><span> </span><span class="attribute">separator</span><span>=</span><span class="attribute-value">","</span><span> </span><span
class="attribute">close</span><span>=</span><span class="attribute-value">")"</span><span class="tag">></span><span> </span></span></li><li><span> #{key}, #{value} </span></li><li><span> <span
class="tag"></</span><span class="tag-name">foreach</span><span class="tag">></span><span> </span></span></li><li><span><span class="tag"></</span><span class="tag-name">select</span><span class="tag">></span><span> </span></span></li></ol></div><pre
name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="14" title="MyBatis的动态SQL详解" style="display: none;">
<select id="dynamicForeachTest" resultType="Blog">
select * from t_blog where id in
<!-- 遍历的对象是Map.Entry时，index代表对应的key，item代表对应的value -->
<foreach collection="collection" index="key" item="value" open="(" separator="," close=")">
#{key}, #{value}
</foreach>
</select></pre>
其对应的接口方法大概是如下这样：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Java代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%20%20%20%20public%20List%3CBlog%3E%20dynamicForeachTest(Set%3CMap.Entry%3CInteger%2C%20Integer%3E%3E%20ids)%3B%0A"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-j"><li><span><span class="keyword">public</span><span> List<Blog> dynamicForeachTest(Set<Map.Entry<Integer, Integer>> ids); </span></span></li></ol></div><pre
name="code" class="java" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#" pre_index="15" title="MyBatis的动态SQL详解" style="display: none;"> public List<Blog> dynamicForeachTest(Set<Map.Entry<Integer, Integer>>
ids);
</pre>
</div>
<div>2、<strong>bind</strong>标签，动态SQL中已经包含了这样一个新的标签，它的功能是在当前OGNL上下文中创建一个变量并绑定一个值。有了它以后我们以前的模糊查询就可以改成这个样子：</div>
<div>
<div class="dp-highlighter" id=""><div class="bar"><div class="tools">Xml代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%20%20%20%20%3Cselect%20id%3D%22fuzzyQuery%22%20resultType%3D%22Blog%22%20parameterType%3D%22java.lang.String%22%3E%20%20%0A%20%20%20%20%09%3C!--%20bind%E6%A0%87%E7%AD%BE%E7%94%A8%E4%BA%8E%E5%88%9B%E5%BB%BA%E6%96%B0%E7%9A%84%E5%8F%98%E9%87%8F%20--%3E%0A%09%09%3Cbind%20name%3D%22titleLike%22%20value%3D%22'%25'%2B_parameter%2B'%25'%22%2F%3E%0A%20%20%20%20%20%20%20%20select%20*%20from%20t_blog%20where%20title%20like%20%23%7BtitleLike%7D%20%20%0A%20%20%20%20%3C%2Fselect%3E"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-xml"><li><span><span> </span><span class="tag"><</span><span class="tag-name">select</span><span> </span><span
class="attribute">id</span><span>=</span><span class="attribute-value">"fuzzyQuery"</span><span> </span><span class="attribute">resultType</span><span>=</span><span class="attribute-value">"Blog"</span><span> </span><span class="attribute">parameterType</span><span>=</span><span
class="attribute-value">"java.lang.String"</span><span class="tag">></span><span> </span></span></li><li><span> <span class="comments"><!-- bind标签用于创建新的变量 --></span><span> </span></span></li><li><span><span
class="tag"><</span><span class="tag-name">bind</span><span> </span><span class="attribute">name</span><span>=</span><span class="attribute-value">"titleLike"</span><span> </span><span class="attribute">value</span><span>=</span><span class="attribute-value">"'%'+_parameter+'%'"</span><span
class="tag">/></span><span> </span></span></li><li><span> select * from t_blog where title like #{titleLike} </span></li><li><span> <span
class="tag"></</span><span class="tag-name">select</span><span class="tag">></span><span> </span></span></li></ol></div><pre name="code" class="xml" codeable_id="" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#"
pre_index="16" title="MyBatis的动态SQL详解" style="display: none;"> <select id="fuzzyQuery" resultType="Blog" parameterType="java.lang.String">
<!-- bind标签用于创建新的变量 -->
<bind name="titleLike" value="'%'+_parameter+'%'"/>
select * from t_blog where title like #{titleLike}
</select></pre>
</div>
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<div id="digg_bottom" class="clearfix"><div class="digged"><strong>43</strong> <br>顶</div><div class="digged"><strong>5</strong> <br>踩</div></div>
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<li>2012-01-09 12:08</li>
<li>浏览 171212</li>
<li><a href="#comments">评论(13)</a></li>
<li>分类:<a href="http://www.iteye.com/blogs/category/language">编程语言</a></li>
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<div class="boutique-curr-box blog_comment">
<div class="boutique-curr clearfix">
<h5 class="h3titles">参考知识库</h5>
<dl class="dlnewlist">
<dd><a target="_blank" href="http://lib.csdn.net/base/ai"><img src="http://img.knowledge.csdn.net/upload/base/1479972981201_201.jpg" width="58" height="58" alt=""></a></dd>
<dt>
<a target="_blank" href="http://lib.csdn.net/base/ai" classs="title">人工智能知识库</a>
<span>
<em>4740</em> 关注 <i>|</i> <em>410</em> 收录
</span>
</dt>
</dl>
<dl class="dlnewlist">
<dd><a target="_blank" href="http://lib.csdn.net/base/mongodb"><img src="http://img.knowledge.csdn.net/upload/base/1478676229520_520.jpg" width="58" height="58" alt=""></a></dd>
<dt>
<a target="_blank" href="http://lib.csdn.net/base/mongodb" classs="title">MongoDB知识库</a>
<span>
<em>5620</em> 关注 <i>|</i> <em>336</em> 收录
</span>
</dt>
</dl>
<dl class="dlnewlist">
<dd><a target="_blank" href="http://lib.csdn.net/base/hbase"><img src="http://img.knowledge.csdn.net/upload/base/1479363734443_443.jpg" width="58" height="58" alt=""></a></dd>
<dt>
<a target="_blank" href="http://lib.csdn.net/base/hbase" classs="title">Hbase知识库</a>
<span>
<em>6472</em> 关注 <i>|</i> <em>63</em> 收录
</span>
</dt>
</dl>
<dl class="dlnewlist">
<dd><a target="_blank" href="http://lib.csdn.net/base/blockchain"><img src="http://img.knowledge.csdn.net/upload/base/1476175342721_721.jpg" width="58" height="58" alt=""></a></dd>
<dt>
<a target="_blank" href="http://lib.csdn.net/base/blockchain" classs="title">区块链知识库</a>
<span>
<em>3121</em> 关注 <i>|</i> <em>108</em> 收录
</span>
</dt>
</dl>
</div>
</div>
<div class="blog_comment">
<h5>评论</h5>
<a id="comments" name="comments"></a>
<div id="bc2394641">
<div class="comment_title">
13 楼
<a href="http://563011992.iteye.com" target="_blank" title="吾乃隔壁老王">吾乃隔壁老王</a>
2016-11-07
</div>
<div class="comment_content">3Q，问个问题啊，where里的if里，能不能不加and?</div>
</div>
<div id="bc2383373">
<div class="comment_title">
12 楼
<a href="http://yuang.iteye.com" target="_blank" title="yuang">yuang</a>
2015-12-29
</div>
<div class="comment_content"><table class="bbcode"><tbody><tr><td><img src="<ul></td></tr><tr><td>[*]</td></tr><tr><td></ul>">" target="_blank"><img src="<ul></td></tr><tr><td>[*]</td></tr><tr><td></ul>">"
/><img src="<ul></td></tr><tr><td>[*]</td></tr><tr><td></ul>">" target="_blank"><img src="<ul></td></tr><tr><td>[*]</td></tr><tr><td></ul>">"
wmode="" quality="high" menu="false" pluginspage="http://www.macromedia.com/go/getflashplayer" type="application/x-shockwave-flash" width="200" height="200"></td><td><img src="/images/smiles/icon_surprised.gif"> </td></tr></tbody></table></div>
</div>
<div id="bc2364106">
<div class="comment_title">
11 楼
<a href="http://happymzw.iteye.com" target="_blank" title="happymzw">happymzw</a>
2014-12-04
</div>
<div class="comment_content"><div class="quote_title">Syhenian 写道</div><div class="quote_div"><div class="dp-highlighter" id=""><div class="bar"><div class="tools">Java代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14"
height="15" flashvars="clipboard=%3Cupdate%20id%3D%22dynamicSetTest%22%20parameterType%3D%22Blog%22%3E%20%20%0A%20%20%20%20update%20t_blog%20%20%0A%20%20%20%20%3Cset%3E%20%20%0A%20%20%20%20%20%20%20%20%3Cif%20test%3D%22title%20!%3D%20null%22%3E%20%20%0A%20%20%20%20%20%20%20%20%20%20%20%20title%20%3D%20%23%7Btitle%7D%2C%20%20%0A%20%20%20%20%20%20%20%20%3C%2Fif%3E%20%20%0A%20%20%20%20%20%20%20%20%3Cif%20test%3D%22content%20!%3D%20null%22%3E%20%20%0A%20%20%20%20%20%20%20%20%20%20%20%20content%20%3D%20%23%7Bcontent%7D%2C%20%20%0A%20%20%20%20%20%20%20%20%3C%2Fif%3E%20%20%0A%20%20%20%20%20%20%20%20%3Cif%20test%3D%22owner%20!%3D%20null%22%3E%20%20%0A%20%20%20%20%20%20%20%20%20%20%20%20owner%20%3D%20%23%7Bowner%7D%20%20%0A%20%20%20%20%20%20%20%20%3C%2Fif%3E%20%20%0A%20%20%20%20%3C%2Fset%3E%20%20%0A%20%20%20%20where%20id%20%3D%20%23%7Bid%7D%20%20%0A%3C%2Fupdate%3E%20%20"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-j"><li><span><span><update id=</span><span class="string">"dynamicSetTest"</span><span> parameterType=</span><span
class="string">"Blog"</span><span>> </span></span></li><li><span> update t_blog </span></li><li><span> <set> </span></li><li><span> <<span
class="keyword">if</span><span> test=</span><span class="string">"title != null"</span><span>> </span></span></li><li><span> title = #{title}, </span></li><li><span> </<span
class="keyword">if</span><span>> </span></span></li><li><span> <<span class="keyword">if</span><span> test=</span><span class="string">"content != null"</span><span>> </span></span></li><li><span> content = #{content}, </span></li><li><span> </<span
class="keyword">if</span><span>> </span></span></li><li><span> <<span class="keyword">if</span><span> test=</span><span class="string">"owner != null"</span><span>> </span></span></li><li><span> owner = #{owner} </span></li><li><span> </<span
class="keyword">if</span><span>> </span></span></li><li><span> </set> </span></li><li><span> where id = #{id} </span></li><li><span></update> </span></li></ol></div><pre
name="code" class="java" codeable_id="2364106" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#bc2364106" pre_index="0" title="MyBatis的动态SQL详解" style="display: none;"><update id="dynamicSetTest" parameterType="Blog">
update t_blog
<set>
<if test="title != null">
title = #{title},
</if>
<if test="content != null">
content = #{content},
</if>
<if test="owner != null">
owner = #{owner}
</if>
</set>
where id = #{id}
</update> </pre><br><br>这段可以这样写吗 如果ownner等于null 那语句就是<br><br>update t_blog title= 'title', content='content'<span style="color: red;">,</span> where id='id'<br><br>多了个红色的逗号不会报错？</div><br><br>楼主说了，set会自动处理掉后面的那个逗号的</div>
</div>
<div id="bc2363317">
<div class="comment_title">
10 楼
<a href="http://1106592119.iteye.com" target="_blank" title="简单就是美了">简单就是美了</a>
2014-11-20
</div>
<div class="comment_content"><img src="/images/smiles/icon_idea.gif"> <img src="/images/smiles/icon_idea.gif"> <img src="/images/smiles/icon_idea.gif"> <img src="/images/smiles/icon_idea.gif"> <img src="/images/smiles/icon_idea.gif"> </div>
</div>
<div id="bc2362264">
<div class="comment_title">
9 楼
<a href="http://shiping8000.iteye.com" target="_blank" title="shiping8000">shiping8000</a>
2014-11-06
</div>
<div class="comment_content">写的不错，给赞 <img src="/images/smiles/icon_idea.gif"> </div>
</div>
<div id="bc2357405">
<div class="comment_title">
8 楼
<a href="http://syhenian.iteye.com" target="_blank" title="Syhenian">Syhenian</a>
2014-08-29
</div>
<div class="comment_content"><div class="dp-highlighter" id=""><div class="bar"><div class="tools">Java代码 <embed wmode="transparent" src="/javascripts/syntaxhighlighter/clipboard_new.swf" width="14" height="15" flashvars="clipboard=%3Cupdate%20id%3D%22dynamicSetTest%22%20parameterType%3D%22Blog%22%3E%20%20%0A%20%20%20%20update%20t_blog%20%20%0A%20%20%20%20%3Cset%3E%20%20%0A%20%20%20%20%20%20%20%20%3Cif%20test%3D%22title%20!%3D%20null%22%3E%20%20%0A%20%20%20%20%20%20%20%20%20%20%20%20title%20%3D%20%23%7Btitle%7D%2C%20%20%0A%20%20%20%20%20%20%20%20%3C%2Fif%3E%20%20%0A%20%20%20%20%20%20%20%20%3Cif%20test%3D%22content%20!%3D%20null%22%3E%20%20%0A%20%20%20%20%20%20%20%20%20%20%20%20content%20%3D%20%23%7Bcontent%7D%2C%20%20%0A%20%20%20%20%20%20%20%20%3C%2Fif%3E%20%20%0A%20%20%20%20%20%20%20%20%3Cif%20test%3D%22owner%20!%3D%20null%22%3E%20%20%0A%20%20%20%20%20%20%20%20%20%20%20%20owner%20%3D%20%23%7Bowner%7D%20%20%0A%20%20%20%20%20%20%20%20%3C%2Fif%3E%20%20%0A%20%20%20%20%3C%2Fset%3E%20%20%0A%20%20%20%20where%20id%20%3D%20%23%7Bid%7D%20%20%0A%3C%2Fupdate%3E%20%20"
quality="high" allowscriptaccess="always" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> <a href="javascript:void()" title="收藏这段代码" onclick="code_favorites_do_favorite(this);return false;"><img class="star"
src="/images/icon_star.png" alt="收藏代码"><img class="spinner" src="/images/spinner.gif" style="display:none"></a></div></div><ol start="1" class="dp-j"><li><span><span><update id=</span><span class="string">"dynamicSetTest"</span><span> parameterType=</span><span
class="string">"Blog"</span><span>> </span></span></li><li><span> update t_blog </span></li><li><span> <set> </span></li><li><span> <<span
class="keyword">if</span><span> test=</span><span class="string">"title != null"</span><span>> </span></span></li><li><span> title = #{title}, </span></li><li><span> </<span
class="keyword">if</span><span>> </span></span></li><li><span> <<span class="keyword">if</span><span> test=</span><span class="string">"content != null"</span><span>> </span></span></li><li><span> content = #{content}, </span></li><li><span> </<span
class="keyword">if</span><span>> </span></span></li><li><span> <<span class="keyword">if</span><span> test=</span><span class="string">"owner != null"</span><span>> </span></span></li><li><span> owner = #{owner} </span></li><li><span> </<span
class="keyword">if</span><span>> </span></span></li><li><span> </set> </span></li><li><span> where id = #{id} </span></li><li><span></update> </span></li></ol></div><pre
name="code" class="java" codeable_id="2357405" codeable_type="BlogComment" source_url="http://elim.iteye.com/blog/1338557#bc2357405" pre_index="0" title="MyBatis的动态SQL详解" style="display: none;"><update id="dynamicSetTest" parameterType="Blog">
update t_blog
<set>
<if test="title != null">
title = #{title},
</if>
<if test="content != null">
content = #{content},
</if>
<if test="owner != null">
owner = #{owner}
</if>
</set>
where id = #{id}
</update> </pre><br><br>这段可以这样写吗 如果ownner等于null 那语句就是<br><br>update t_blog title= 'title', content='content'<span style="color: red;">,</span> where id='id'<br><br>多了个红色的逗号不会报错？</div>
</div>
<div id="bc2351761">
<div class="comment_title">
7 楼
<a href="http://slc2006119.iteye.com" target="_blank" title="slc2006119">slc2006119</a>
2014-06-27
</div>
<div class="comment_content">简单，易懂，确实写的不错，赞一个！</div>
</div>
<div id="bc2350561">
<div class="comment_title">
6 楼
<a href="http://schnauzer.iteye.com" target="_blank" title="dmewy">dmewy</a>
2014-06-12
</div>
<div class="comment_content">不错 适合开发初期看</div>
</div>
<div id="bc2349324">
<div class="comment_title">
5 楼
<a href="http://songjianyong.iteye.com" target="_blank" title="宋建勇">宋建勇</a>
2014-05-28
</div>
<div class="comment_content">今天整合MyBatis，帮了大忙了啊！不错啊！<img src="/images/smiles/icon_idea.gif"> </div>
</div>
<div id="bc2348923">
<div class="comment_title">
4 楼
<a href="http://xiaoyaya751.iteye.com" target="_blank" title="18289753290">18289753290</a>
2014-05-23
</div>
<div class="comment_content">不错<img src="/images/smiles/icon_idea.gif"> <img src="/images/smiles/icon_idea.gif"> </div>
</div>
<div id="bc2342280">
<div class="comment_title">
3 楼
<a href="http://lcg19880128.iteye.com" target="_blank" title="lcg19880128">lcg19880128</a>
2014-03-14
</div>
<div class="comment_content"><img src="/images/smiles/icon_idea.gif"> <img src="/images/smiles/icon_idea.gif"> <img src="/images/smiles/icon_idea.gif"> </div>
</div>
<div id="bc2339107">
<div class="comment_title">
2 楼
<a href="http://coffeeboy2012.iteye.com" target="_blank" title="coffeeBoy2012">coffeeBoy2012</a>
2014-02-07
</div>
<div class="comment_content"><img src="/images/smiles/icon_idea.gif"> 很详细</div>
</div>
<div id="bc2332128">
<div class="comment_title">
1 楼
<a href="http://huxiulei.iteye.com" target="_blank" title="huxiulei">huxiulei</a>
2013-11-22
</div>
<div class="comment_content">嗯 写的不错... 简明易懂</div>
</div>
</div>
<div class="blog_comment">
<h5>发表评论</h5>
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