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> |
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> |
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> |
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
