mybatis中如何实现一对一,一对多的关联查询呢?
下文笔者讲述mybatis中一对一和一对多关联查询的简介说明,如下所示
实现思路:
只需在resultmap定义时
指定多个对象即可
例:
<mapper namespace="com.java265.userMapper">
<!--association 一对一关联查询 -->
<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.java265.Classes" id="ClassesResultMap">
<!-- 实体类的字段名和数据表的字段名映射 -->
<id property="id" column="c_id"/>
<result property="name" column="c_name"/>
<association property="teacher" javaType="com.java265.Teacher">
<id property="id" column="t_id"/>
<result property="name" column="t_name"/>
</association>
</resultMap>
<!--collection 一对多关联查询 -->
<select id="getClass2" parameterType="int" resultMap="ClassesResultMap2">
select * from class c,teacher t,student s where c.teacher_id=t.t_id and c.c_id=s.class_id and c.c_id=#{id}
</select>
<resultMap type="com.java265.Classes" id="ClassesResultMap2">
<id property="id" column="c_id"/>
<result property="name" column="c_name"/>
<association property="teacher" javaType="com.java265.Teacher">
<id property="id" column="t_id"/>
<result property="name" column="t_name"/>
</association>
<collection property="student" ofType="com.java265.Student">
<id property="id" column="s_id"/>
<result property="name" column="s_name"/>
</collection>
</resultMap>
</mapper>
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