1.使用 resultMap 實現關聯單個對象(聯合查詢方式)

<resultMap type="Student" id="stuMap1">
    <id column="sid" property="id"/>
    <result column="sname" property="name"/>
    <result column="age" property="age"/>
    <result column="tid" property="tid"/>
    <association property="teacher"
 
 javaType="Teacher" >

        <id column="tid" property="id"/>
        <result column="tname" property="name"/>
    </association>
</resultMap>

<select id="selAll1" resultMap="stuMap1">
    select s.id sid,s.name sname,age age,t.id tid,t.name tname
     
    FROM student s left outer join teacher t on s.tid=t.id
 
</select>    

註意id為selAll1的select標簽與下面id為selAll的select標簽的區別

　　　　　　<resultMap type="student" id="stuMap">
              <id column="id" property="id"/>
              <result column="name" property="name"/>
              <result column="age" property="age"/>
              <
 
result column="tid" property="tid"/>
              <association property="teacher" javaType="Teacher" column="tid" select="com.xxx.mapper.TeacherMapper.selById" >
              </association>
          </resultMap>
          <select id="selAll" resultMap="stuMap">
              select * from student
          </select>

第一中是聯合查詢，第二中不是，是先查詢每一個學生，然後再根據學生的tid去查詢老師，第二種實現效率低

mybatis學習 十四 resultMap標簽 一對一(聯合查詢)