关键字：association 一对一映射（一个班级只有一个班主任）
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<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>
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关键字：collection 一对多映射（一个老师有多个学生）
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<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>
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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
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<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>
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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服务器之家网站的支持！
原文链接：https://blog.csdn.net/weixin_38048680/article/details/80307466