mybatis使用association的resultMap方式进行映射少数据问题

在第一次使用mybatis的复杂映射的时候发现映射出来的对象的数量和那sql直接去库里面查的数量要少。

public class Blog {
private int id;
private String title;
private String content;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}

}

public class BlogDetail {
private Blog blog;
private int commentCount;
public Blog getBlog() {
return blog;
}
public void setBlog(Blog blog) {
this.blog = blog;
}
public int getCommentCount() {
return commentCount;
}
public void setCommentCount(int commentCount) {
this.commentCount = commentCount;
}

}

我使用的方式是如下方式：

<resultMap type="BlogDetail" id="blogDetailResultMap">
<result property="commentCount" column="comment_count" />
<association property="blog" column="blog_id" javaType="Blog" resultMap="blogResultMap" />
</resultMap>

<resultMap type="Blog" id="blogResultMap">
<id property="id" column="blog_id" />
<result property="title" column="title" />
<result property="content" column="content" />
</resultMap>

<select id="selectByID" parameterType="int" resultMap="detailBlogResultMap">
select
B.id as blog_id ,
B.title as blog_title ,
B.content as blog_content ,
（select count(*) from tb_comment C where C.blog_id=B.id） as  comment_count
from tb_blog B
where B.id = #{id}
</select>

程序跑起来，没有任何的报错。但是mybatis映射出来的对象的数量比sql直接在数据库里面查出来的要少。

对比参考的资料，发现我的第一个resultMap 中少一个主键。

按照这个思路最终发现少数据原因是blogDetailResultMap中comment_count都是一样的。

mybatis的复杂映射参照：

/article/7843625.html

原文如下：

<resultMap type="Blog" id="detailBlogResultMap03">
<!-- 注意这里的id -->
<id property="id" column="blog_id" />
<result property="title" column="blog_title" />
<result property="content" column="blog_content" />
<result property="pubTime" column="blog_pub_time" />
<association property="author" column="blog_user_id" javaType="User" resultMap="authorResultMap03" />
<collection property="comments" column="comment_blog_id" ofType="Comment"  resultMap="commentResultMap03" />
</resultMap>

<resultMap type="User" id="authorResultMap03">
<!-- 注意这里的id -->
<id property="id" column="user_id" />
<result property="title" column="title" />
<result property="password" column="user_password" />
<result property="userName" column="user_user_name" />
<result property="userAge" column="user_user_age" />
<result property="userAddress" column="user_user_address" />
</resultMap>

<resultMap type="Comment" id="commentResultMap03">
<id property="id" column="comment_id" />
<result property="content" column="comment_content" />
</resultMap>

<select id="selectByID03" parameterType="int" resultMap="detailBlogResultMap">
select
B.id as blog_id ,
B.title as blog_title ,
B.content as blog_content ,
B.pub_time as blog_pub_time ,
B.user_id as blog_user_id ,
U.id as user_id,
U.password as user_password,
U.user_name as user_user_name ,
U.user_age as user_user_age ,
U.user_address as user_user_address ,
C.id as comment_id ,
C.blog_id as comment_blog_id ,
C.content as comment_content
from `blog` B
left outer join `user` U on B.user_id = U.id
left outer join `comment` C on B.id = C.blog_id
where B.id = #{id}
</select>