mybatis 一对一、一对多和多对多查询实例代码

关键字：association 一对一映射（一个班级只有一个班主任）

 <select id="getClass" parameterType="int" resultMap="ClassesResultMap">      select * from class c,teacher t where c.teacher_id=t.t_id and c.c_id=#{id}    </select>    <resultMap type="com.lcb.user.Classes" id="ClassesResultMap">      <id property="id" column="c_id"/>      <result property="name" column="c_name"/>      <association property="teacher" javaType="com.lcb.user.Teacher">        <id property="id" column="t_id"/>        <result property="name" column="t_name"/>      </association>    </resultMap>  

关键字：collection 一对多映射（一个老师有多个学生）

<resultMap type="Teacher" id="teacherMaps">      <id column="id" property="id"/>      <result column="name" property="name"/>      <result column="class_name" property="className"/>      <collection property="students" ofType="Student" select="getStudents" column="id">      </collection>    </resultMap>    <!-- 查询所有的老师级各自的所有学生 -->    <select id="getAllTeacher" parameterType="Teacher" resultMap="teacherMaps">      SELECT        t.id,        t.NAME,        t.class_name      FROM        teacher t    </select>    <select id="getStudents" parameterType="int" resultType="Student">      select         s.id,        s. NAME,        s.class_name as className      from student s      where teacher_id = #{id}    </select> 

关键字：association 多对一映射（多个人属于一个国家）

多对一相当于一对多，也可以使用collection

<select id="selectCountry" resultType="Country">    select cid,cname from country where cid=#{ooo}  </select>  <resultMap type="People" id="peopleMapper2">    <id column="pid" property="pid"/>    <result column="pname" property="pname"/>    <association property="country"            javaType="Country"           select="selectCountry"           column="countryId" />  </resultMap>    <select id="selectById2" resultMap="peopleMapper2">    select pid,pname,countryId from people where pid = #{xxx}  </select>  

总结

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