mybatis-1vN

<!-- 非常复杂的语句 -->
<select id="selectBlogDetails" resultMap="detailedBlogResultMap">
  select
       B.id as blog_id,
       B.title as blog_title,
       B.author_id as blog_author_id,
       A.id as author_id,
       A.username as author_username,
       A.password as author_password,
       A.email as author_email,
       A.bio as author_bio,
       A.favourite_section as author_favourite_section,
       P.id as post_id,
       P.blog_id as post_blog_id,
       P.author_id as post_author_id,
       P.created_on as post_created_on,
       P.section as post_section,
       P.subject as post_subject,
       P.draft as draft,
       P.body as post_body,
       C.id as comment_id,
       C.post_id as comment_post_id,
       C.name as comment_name,
       C.comment as comment_text,
       T.id as tag_id,
       T.name as tag_name
  from Blog B
       left outer join Author A on B.author_id = A.id
       left outer join Post P on B.id = P.blog_id
       left outer join Comment C on P.id = C.post_id
       left outer join Post_Tag PT on PT.post_id = P.id
       left outer join Tag T on PT.tag_id = T.id
  where B.id = #{id}
</select>



<!-- 非常复杂的结果映射 -->
<resultMap id="detailedBlogResultMap" type="Blog">
  <constructor>
    <idArg column="blog_id" javaType="int"/>
  </constructor>
  <result property="title" column="blog_title"/>
  <association property="author" javaType="Author">
    <id property="id" column="author_id"/>
    <result property="username" column="author_username"/>
    <result property="password" column="author_password"/>
    <result property="email" column="author_email"/>
    <result property="bio" column="author_bio"/>
    <result property="favouriteSection" column="author_favourite_section"/>
  </association>
  <collection property="posts" ofType="Post">
    <id property="id" column="post_id"/>
    <result property="subject" column="post_subject"/>
    <association property="author" javaType="Author"/>
    <collection property="comments" ofType="Comment">
      <id property="id" column="comment_id"/>
    </collection>
    <collection property="tags" ofType="Tag" >
      <id property="id" column="tag_id"/>
    </collection>
    <discriminator javaType="int" column="draft">
      <case value="1" resultType="DraftPost"/>
    </discriminator>
  </collection>
</resultMap>

• association – 一个复杂类型的关联；( 1 v 1 )

• 嵌套结果映射 – 关联可以是 resultMap 元素，或是对其它结果映射的引用

•   A.id as author_id,
           A.username as author_username,
           A.password as author_password,
           A.email as author_email,
           A.bio as author_bio,
           A.favourite_section as author_favourite_section,
    
    <association property="author" javaType="Author">
        <id property="id" column="author_id"/>
        <result property="username" column="author_username"/>
        <result property="password" column="author_password"/>
        <result property="email" column="author_email"/>
        <result property="bio" column="author_bio"/>
        <result property="favouriteSection" column="author_favourite_section"/>
      </association>
    
  

• collection – 一个复杂类型的集合 ( 1 v N )

  • 嵌套结果映射 – 集合可以是 resultMap 元素，或是对其它结果映射的引用

  •   Block{
      Author author;
      List<Post> posts;
      }
      
      Post{
       Author author;
       List<Comment> comments;
       List<Tag> tags;
       DraftPost draftPost;//等于1时候，查出草稿
      }
      
      <association property="author" javaType="Author">
          <id property="id" column="author_id"/>
          <result property="username" column="author_username"/>
          <result property="password" column="author_password"/>
          <result property="email" column="author_email"/>
          <result property="bio" column="author_bio"/>
          <result property="favouriteSection" column="author_favourite_section"/>
        </association>
        <collection property="posts" ofType="Post">
          <id property="id" column="post_id"/>
          <result property="subject" column="post_subject"/>
          <association property="author" javaType="Author"/>
          <collection property="comments" ofType="Comment">
            <id property="id" column="comment_id"/>
          </collection>
          <collection property="tags" ofType="Tag" >
            <id property="id" column="tag_id"/>
          </collection>
          <discriminator javaType="int" column="draft">
            <case value="1" resultType="DraftPost"/>
          </discriminator>
        </collection>
      
    

• discriminator – 使用结果值来决定使用哪个 resultMap.  鉴别器

• case – 基于某些值的结果映射

• 嵌套结果映射 – case 也是一个结果映射，因此具有相同的结构和元素；或者引用其它的结果映射