如何将Android数据库操作通用化（一）

概述
小小说明
一别之后二地相悬
都说是三四月谁又知五六年
七弦琴无心弹八行书不可传
九连环从中折断十里长亭望眼欲穿
披荆斩棘

概述

在开始考虑Android的数据库操作之前，我们先回想一下Web方面的数据库操作。如果我们只是停留在JDBC的简单使用和封装上（比如纯JDCB，或者DBUtils），即使我们对数据库的增删改查操作进行了接口的抽取，代码依旧会和业务有很强的耦合性。

经过我们分析，解除耦合性的关键在于如何解决自动映射“实体类 与 数据库表”之间的对应关系。如果能够做到这一步，那么我们就能够更好的解耦了，也能降低我们的代码重复率。

如果我们再跨前一步，使用更为优秀的框架（比如：Hibernate），这一切都会变得简单和方便。Hibernate为我们提供了两种建立“实体类（bean） - 数据库表”之间关系的方式。

一种是使用配置文件，在配置文件中对表名、字段、实体间的关系进行配置，Hibernate就能够为我们做好一切，下面提供一段配置文件示例：

<code class="language-xml hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">hibernate-mapping</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">package</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"com.bzh.gt.bean"</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">class</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"Apartment"</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">id</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"id"</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">generator</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"native"</span>/></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">id</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">property</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"name"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">length</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"10"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">not-null</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"true"</span>/></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">property</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"rank"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">not-null</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"true"</span>/></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">property</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"sex"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">not-null</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"true"</span>/></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">property</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"topFloor"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">not-null</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"true"</span>/></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">property</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"roomNumber"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">not-null</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"true"</span>/></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">property</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"bedNumber"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">not-null</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"true"</span>/></span>

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;"><!-- dormitories属性，本类与Dormitory的一对多关系 --></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">set</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dormitories"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">inverse</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"true"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">lazy</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"extra"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">fetch</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"select"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">cascade</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"all-delete-orphan"</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">key</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">column</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"apartmentId"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">key</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">one-to-many</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"Dormitory"</span>/></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">set</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">class</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">hibernate-mapping</span>></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li></ul>

另一种，则是使用注解的方式。Hibernate为我们提供了

@Entity

、

@Table

、

@Id

、

@Column

、

@GeneratedValue

诸如此类很多的注解。我们只需要在合适的地方加上这些注解，为我们的类、字段配置好关系，Hibernate也能够为我们做好一切，下面提供一段配置文件示例：

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Entity</span>(name=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"brand"</span>) <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 实体bean */</span>
<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Table</span>(name=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"brand_t"</span>) <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 指定生成表的名字*/</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Brand</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">implements</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Serializable</span> {</span>

<span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @Fields</span> code : ID使用UUID生成 **/</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> String code;
<span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @Fields</span> name : 品牌名称 **/</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> String name;
<span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @Fields</span> visible : 是否可见 **/</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Boolean visible = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;
<span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @Fields</span> logopath : logo路径 **/</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> String logopath;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">Brand</span>(String name, String logopath) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.name = name;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.logopath = logopath;
}
<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Id</span>
<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Column</span>(name=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"code"</span>, length=<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">36</span>) <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* UUID是36 */</span>
<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@GeneratedValue</span>(generator = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"system-uuid"</span>)
<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@GenericGenerator</span>(name = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"system-uuid"</span>, strategy = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"uuid"</span>)
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> String <span class="hljs-title" style="box-sizing: border-box;">getCode</span>() {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> code;
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">setCode</span>(String code) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.code = code;
}
<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Column</span>(length=<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">40</span>, nullable=<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>)
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> String <span class="hljs-title" style="box-sizing: border-box;">getName</span>() {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> name;
}
<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Column</span>(nullable=<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>)
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> Boolean <span class="hljs-title" style="box-sizing: border-box;">getVisible</span>() {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> visible;
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*/images/brand/2012/12/8/9/sss.gif */</span>
<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Column</span>(length=<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">80</span>,nullable=<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>)
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> String <span class="hljs-title" style="box-sizing: border-box;">getLogopath</span>() {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> logopath;
}

}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li></ul>

番外话说完，回到我们热爱的Android中，我们应该如何在Android写出一个通用的数据库增删改查操作，可能也需要借鉴Hibernate的优秀思想。

不过，世间万物都是一步一步进行演化的，我们的代码同样是如此，从不通用到通用，我会通过几篇博客一一向大家展示，但是由于本人经验和学识有限，无法构建出一个完整的开源项目，望大家海涵。有兴趣的可以联系我大家一起尝试做一下（每当你在感叹，如果有这样一个东西就好了的时候，请注意，其实这是你的机会）。

小小说明

整个例子会以一条新闻实体作为基本元素，并贯穿整个例子。新闻实体很简单，我们给它起个名字叫做

News

，字段由

id

、

title

、

summary

构成。以下是示例代码：

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">News</span> {</span>

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> id;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> String title;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> String summary;

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 此处省略get、set方法</span>
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>

另外，在SQLite数据库中，存东西绝大多数是String类型的，只有涉及到主键、自增的才会使用int。

最后，想章节名太痛苦，就在网上找了一些有趣的诗词作为章节了，大家按顺序看哦。

一别之后，二地相悬。

实体对象我们已经有了，那么现在就差数据库表了。现在回想一下Android中，数据库表的操作步骤，继承SQLiteOpenHelper，修改一些构造函数，再在onCreate中使用db执行一下建表语句，好像就完成了（数据库版本升级后续再讲）。请看示例代码：

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">DBHelper</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">SQLiteOpenHelper</span> {</span>

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> VERSION = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> String NAME = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"bzh.db"</span>;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">DBHelper</span>(Context context) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>(context, NAME, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>, VERSION);
}

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 新闻表：主键+标题+摘要</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> String TABLE_ID = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"_id"</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> String TABLE_NEWS_NAME = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"news"</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> String TABLE_NEWS_TITLE = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"title"</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> String TABLE_NEWS_SUMMARY = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"summary"</span>;

<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onCreate</span>(SQLiteDatabase db) {
db.execSQL(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"CREATE TABLE "</span> + TABLE_NEWS_NAME + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"( "</span> + <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//</span>
TABLE_ID + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" integer primary key autoincrement , "</span> + <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//</span>
TABLE_NEWS_TITLE + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" varchar(50) ,"</span> + <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//</span>
TABLE_NEWS_SUMMARY + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" varhcar(200))"</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//</span>
);

}

<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onUpgrade</span>(SQLiteDatabase db, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> oldVersion, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> newVersion) {
}

}
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li></ul>

仔细看一下代码，其中我们把各个字段和表名都抽取成为了常量字段，这样可以更方便我们写数据库增删改查操作的时候使用。

都说是三四月，谁又知五六年。

现在，实体和表都有了，是时候写增删改查的操作了。既然是增删改查，那么肯定有对应的

insert

、

delete

、

update

、

findAll

等操作咯。 

而我们作为有经验的开发人员（偷笑），肯定是要面向接口编程咯，那就先写一个

NewsDao

吧，整体上很简单，就不写注释了。代码如下：

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">interface</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">NewsDao</span> {</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> insert(News news);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> delete(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> id);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> update(News news);
List<News> findAll();
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

看起来一切都很顺利，下面是时候写Dao的实现类了，我们就叫做

NewsDaoImpl

吧，并实现

NewsDao

接口。代码如下:

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">NewsDaoImpl</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">implements</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">NewsDao</span> {</span>

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Context context;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> DBHelper helper;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> SQLiteDatabase db;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">NewsDaoImpl</span>(Context context) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.context = context;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.helper = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> DBHelper(context);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.db = helper.getWritableDatabase();
}

<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> <span class="hljs-title" style="box-sizing: border-box;">insert</span>(News news) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
}

<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-title" style="box-sizing: border-box;">delete</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> id) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
}

<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-title" style="box-sizing: border-box;">update</span>(News news) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
}

<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> List<News> <span class="hljs-title" style="box-sizing: border-box;">findAll</span>() {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;
}
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li></ul>

貌似架子就是这个样子了，为了执行增删改查等语句，我们需要一个之前写的DBHelper实例，而DBHelper又要求传入Context对象。然后DBHelper又给了我们一个操作数据库SQLiteDatabase实例。

一切很顺利，不过增删改查方法都是空着的，看来接下来只需要填空就好了。

七弦琴无心弹，八行书不可传。

既然是填空，那么我们就只能一个一个来了，太麻烦了（怪不得程序员喜欢偷懒，喵喵！）。

就先从

insert

开始吧。

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> <span class="hljs-title" style="box-sizing: border-box;">insert</span>(News news) {
ContentValues values = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ContentValues();
values.put(DBHelper.TABLE_NEWS_TITLE, news.getTitle());
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// ... 此处省略N行代码</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> db.insert(DBHelper.TABLE_NEWS_NAME, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>, values);
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>

当然，我这些只是示例性的代码，你看省略的好多呢，整个

insert

的内容一点也不复杂。首先，把字段名和实体字段的对应关系存一个一个入

ContentValues

中，然后再执行一下

db.insert

，并填入要插入的表名和数据，搜一的一下，就成功了。

接下来是

delete

，这么貌似更容易了。在

delete

中指定表的名称、过滤条件、以及过滤条件对应的参数，就OK了。

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-title" style="box-sizing: border-box;">delete</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> id) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> db.delete(DBHelper.TABLE_NEWS_NAME, DBHelper.TABLE_ID + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"=?"</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> String[] { id + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">""</span> });
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

下面是

update

方法。为更新准备一下数据，在

update

填入对应的表名、更新值、过滤条件、以及过滤条件对应的参数，这就完成了。当然，为了偷懒，还是省略了一下代码。我保证下个肯定写完整。

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-title" style="box-sizing: border-box;">update</span>(News news) {
ContentValues values = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ContentValues();
values.put(DBHelper.TABLE_NEWS_TITLE, news.getTitle());
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// ... 此处省略N行代码</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> db.update(DBHelper.TABLE_NEWS_NAME, values, DBHelper.TABLE_ID + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"=?"</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> String[] { news.getId() + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">""</span> });
}
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>

轮到

findAll

方法了，这个比较重要，大家仔细听。我们通过

db.query()

查询数据，并获取到游标（不要忘记关闭哦），然后就开始移动游标，拿出数据并封装到

News

实体中，然后再一个一个加入到

List

中。好吧，我承认，这里又偷懒了，嘿嘿。

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> List<News> <span class="hljs-title" style="box-sizing: border-box;">findAll</span>() {
List<News> result = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// List<M></span>
Cursor cursor = db.query(DBHelper.TABLE_NEWS_NAME, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (cursor != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {
result = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ArrayList<News>();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (cursor.moveToNext()) {
News news = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> News(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// M m  = new M();</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> columnIndex = cursor.getColumnIndex(DBHelper.TABLE_NEWS_NAME);
String title = cursor.getString(columnIndex);
news.setTitle(title);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// ... 此处省略N行代码</span>

result.add(news);
}
}

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 关闭游标</span>
cursor.close();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> result;
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li></ul>

一步一步下来，貌似一个有关

News

实体的增删改查的

Dao

就出炉了，但是，作为一名程序员，写一个这样子的还是可以承受的，那么万一有更多的

User

、

AAA

、

BBB

、

CCC

 等等出现怎么办？

难道还要写出来一大堆

UserDao

、

UserDaoImpl

、

AAADao

、

AAADaoImpl

等等的一大堆类和方法？
老天，你还是杀了我吧。

那么，问题来了，上述的代码需要解决什么问题，才能变成通用的？

九连环从中折断，十里长亭望眼欲穿！

接下来我们从

insert

、

delete

、

update

、

findAll

这些方法中依次分析，看看是哪些问题阻挡了我们通用化的脚步。

insert

中，

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">ContentValues values = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ContentValues();
values.put(DBHelper.TABLE_NEWS_TITLE, news.getTitle());
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// ... 此处省略N行代码</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

如果这些代码能够，以一种“自动”的方式，那么我们的双手就算解放出来一步了，我们需要面对的问题是：如何将实体中的数据，按照对应关系导入到对应的表之中。

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> db.insert(DBHelper.TABLE_NEWS_NAME, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>, values);</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

再看看这句，好像在Java中，写死就等于耦合、等于不方便。而

DBHelper.TABLE_NEWS_NAME

好像也固定在语句之中了，看来这句代码也阻挡了我们解放双手的步伐，嘿嘿，又出来一个。我们需要面对的问题是：如何获取表名。

这个方法是没有了，接下来看看

delete

，

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> db.delete(DBHelper.TABLE_NEWS_NAME, DBHelper.TABLE_ID + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"=?"</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> String[] { id + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">""</span> });</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

其中的

DBHelper.TABLE_NEWS_NAME

我们已经记录下来了，那么，后面的

DBHelper.TABLE_ID

又是怎么回事？
哦，原来是主键，也是固定写死的。看来这也是我们面对的问题：明确实体中的主键是谁，并获取到主键中封装的值。

再看看

update

方法，仔细瞅瞅~ 好像没有耶！那么就继续下一个

findAll

方法。

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">News news = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> News(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// M m  = new M();</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> columnIndex = cursor.getColumnIndex(DBHelper.TABLE_NEWS_NAME);
String title = cursor.getString(columnIndex);
news.setTitle(title);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// ... 此处省略N行代码</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

这里是将游标中的数据取出来，并放入到对应的实体属性中去，这里最容易出现错误、并且也是写死的。看来这里也是问题之一：将数据库表中列的数据，按照对应关系导入到实体之中。

分析完后，我们已经可以总结出一二三四五六七八条了。哈哈。（貌似没有这么多。）

披荆斩棘

需要解决什么问题，才能变成通用的？① 表名的获取② 如何将实体中的数据，按照对应关系导入到对应的表之中。③ 明确实体中的主键是谁，并获取到主键中封装的值。④ 搞定实体对象的创建⑤ 将数据库表中列的数据，按照对应关系导入到实体之中。
以上就是全部问题所在了，如果能够搞定这些，在Android中的数据库通用操作也就应运而生了。



时间是怎样一种东西，它能改变一切、带走一切、更可留下一切。昨天仿佛还在眼前，今天却悄悄过去，我们的生命总是那么有限，那些属于你我的年轻亦是如此缥缈，拥有时并无察觉，待往事已成过眼云烟，方才了解自己荒废了那大好的时光，岁月仍在，流星划过的刹那，却忘记在心中默默许下那卑微的心愿。


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