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脚本之家网站的支持！