Mybatis 高级结果映射 ResultMap Association Collection

Mybatis处理复杂Sql(association/collection)

1. 多对一

• 多个学生，对应一个老师
• 学生：关联--多个学生关联一个老师（多对一）
• 老师：集合--一个老师有很多学生（一对多）

1.1、按照查询嵌套处理

<select id="getStudent" resultMap="StudentTeacher">
    select * from student
</select>
<resultMap id="StudentTeacher" type="Student">
    <result column="id" property="id"/>
    <result column="name" property="name"/>
    <!--复杂属性单独处理
                对象：association
                集合：collection
            -->
    <association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
    <collection property=""/>
</resultMap>
<select id="getTeacher" resultType="Teacher">
    select * from teacher where id = #{tid};
</select>

1.2、按照结果嵌套处理

<select id="getStudent2" resultMap="StudentTeacher2">
    select s.id sid,s.name sname,t.name tname
    from student s,teacher t
    where s.id = t.id
</select>
<resultMap id="StudentTeacher2" type="Student">
    <result column="sid" property="id"/>
    <result column="sname" property="name"/>
    <!--复杂属性单独处理
            对象：association
            集合：collection
        -->
    <association property="teacher" javaType="Teacher">
        <result column="tname" property="name"/>
    </association>
    <collection property=""/>
</resultMap>

2. 一对多

   

<select id="getTeacher"resultMap="TeacherStudent">
      select s.id sid,s.name sname,t.name tname,t.id tid
      from student s,teacher t
      where s.tid = t.id = #{tid}
  </select>
  <resultMap id="TeacherStudent" type="Teacher">
      <result property="id" column="tid"/>
      <result property="name" column="tname"/>
      <collection property="students" ofType="Student">
          <result column="sid" property="id"/>
          <result column="sname" property="name"/>
          <result column="tid" property="tid"/>
      </collection>
  </resultMap>