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
以上所述是小编给大家介绍的mybatis 一对一、一对多和多对多查询,希望对大家有所帮助,如果大家有任何疑问请给我留言,小编会及时回复大家的。在此也非常感谢大家对亿速云网站的支持!
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