论：一对多：（举例一个省有多个市）就是实体类中有（市）类型集合属性；多对一：（多个市有一个共同的省）就是类中有（省）类型的属性。下面来介绍：一对一、多对一的使用方式。
一对多方：
package mlq.bean;import java.io.Serializable;import java.util.List;public class Country implements Serializable { private Integer cid; private String cname; private List<Provincial> list;
get、set 省略...}多对一方：
package mlq.bean;import java.io.Serializable;public class Provincial implements Serializable { private Integer pid; private String pname; private Integer countryid; private Country country;get、set 省略...
}
映射文件配置：（仅供参考）
<!--使用懒加载技术实现查询-->
<select id="allLzcCountry" resultMap="MyLzcCountrys">
SELECT `cid`,`cname` FROM `country` AS a
WHERE a.`cid`=#{id} </select>
<select id="allLzcCountrys" resultType="Provincial">
select pid,pname,countryid from provincial AS b where b.countryid=#{cid} </select>
<resultMap id="MyLzcCountrys" type="Country">
<id property="cid" column="cid"/>
<result property="cname" column="cname"/>
<!--一对多实体类中的集合赋值--> <collection property="list" ofType="Provincial" select="allLzcCountrys" column="cid">
<id property="pid" column="pid"/>
<result property="pname" column="pname"/>
</collection>
</resultMap> <!--使用延迟加载技术实现多对一的关系-->
<!--首先根据查询id查询省会-->
<select id="selectProvincialByid" resultMap="MeMap">
SELECT `pid`,`pname`,`countryid` FROM `provincial`
WHERE `pid`=#{pid} </select>
<!--再根据省会查询出来的id查询国家-->
<select id="selectCountryByid" resultType="Country">
SELECT `cid`,`cname` FROM `country` WHERE `cid`=#{cid} </select>
<resultMap id="MeMap" type="Provincial">
<id property="pid" column="pid"/>
<result property="pname" column="pname"/>
<result property="countryid" column="countryid"/>
<!--根据省会查询出来的id查询国家--> <association property="country" javaType="Provincial" select="selectCountryByid" column="countryid"/>
</resultMap>多对多：（举例老师和学生）就是双方都有集合类属性（多对多的实现需要第三张表维持关联关系，不需要显示具体的实体类）
package mlq.bean;import java.util.List;/**
* 学生类 */public class Student { private Integer sid; private String sname; private Integer age; private List<Teacher> teachers; get、set 省略...}package mlq.bean;import java.util.List;/**
* 教师类 */public class Teacher { private Integer id; private String name; private Integer tid; private List<Student> students;
get、set 省略...
}映射文件配置：
<resultMap id="studentMap" type="Student">
<id property="sid" column="sid"></id>
<result property="sname" column="sname"/>
<result property="age" column="age"/> <collection property="teachers" ofType="Teacher">
<id property="id" column="id"/>
<result property="name" column="name"/>
<result property="tid" column="tid"/>
</collection>
</resultMap>
<select id="findAllByStudent" resultMap="studentMap">
SELECT s.`sid`,s.`sname`,s.`age`,t.`id`,t.`name`,t.`tid`
FROM `student` AS s,`middle` AS m,`teacher` AS t
WHERE s.`sid`=m.`sid` AND m.`tid`=t.`tid` AND s.sid=#{id} </select>
<--以上为学生--> <resultMap id="teacherMap" type="Teacher">
<id property="id" column="id"/>
<result property="name" column="name"/>
<result property="tid" column="tid"/>
<collection property="students" ofType="Student">
<id property="sid" column="sid"></id>
<result property="sname" column="sname"/>
<result property="age" column="age"/>
</collection>
</resultMap>
<select id="findAllByTeacher" resultMap="teacherMap">
SELECT s.`sid`,s.`sname`,s.`age`,t.`id`,t.`name`,t.`tid`
FROM `student` AS s,`middle` AS m,`teacher` AS t
WHERE s.`sid`=m.`sid` AND m.`tid`=t.`tid` AND t.`tid`=#{id}
</select>
以上为关键代码的展示。