mybaits中查询中对象中存在对象（可能是单一对象，可能是集合）

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User和Department数据为多对一

实体对象：

User

属性：

id Integer,name String,Department department

Department

属性

id Integer,name String,sn String

mapper.xml中配置问题件

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.tabchanj.mybatis.domain.UserMapper">    <resultMap type="com.tabchanj.mybatis.domain.User" id="UserMap">        <!-- User的基本属性 -->        <id property="id" column="id"/>        <result property="name" column="name"/>        <!--         　　property:表示本类中关联的对象属性 　　　　　　  并将关联对象的列名的别名与关联对象的属性做对应        -->        <association property="dept" javaType="Department">            <id column="dept_id" property="id" />            <result column="dept_name" property="name" />            <result column="dept_sn" property="sn" />        </association>    </resultMap>    <select id="get" parameterType="Long" resultMap="UserMap">        <!-- 此时先将department的数据一并查询出来 -->        select u.*,d.name dept_name,d.sn dept_sn from t_user u LEFT JOIN t_department d on u.dept_id=d.id where u.id = #{cc}    </select>    <select id="list" resultMap="UserMap">        select u.*,d.name dept_name,d.sn dept_sn from t_user u LEFT JOIN t_department d on u.dept_id=d.id    </select></mapper>

-----------Department的mapper映射配置文件----------<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.tabchanj.mybatis.domain.DepartmentMapper">    <resultMap type="Department" id="DepartmentMap"/>    <select id="get" parameterType="Long" resultMap="DepartmentMap">        select * from t_department where id = #{id}    </select>    <select id="list" resultMap="DepartmentMap">        select * from t_department    </select></mapper>

改进的User的Mapper.xml配置文件

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.tabchanj.mybatis.domain.UserMapper">    <resultMap type="com.tabchanj.mybatis.domain.User" id="UserMap">        <!-- User的基本属性 -->        <id property="id" column="id" />        <result property="name" column="name" />        <!--              property:表示本类中关联的对象属性             columnPrefix:表示关联对象的列名前都有             dept_ resultMap:指明返回的类型时department类型,之一resultMap路径department的mapper映射配置文件中的resultMap的路径          -->        <association property="dept" javaType="Department"            columnPrefix="dept_"            resultMap="com.tabchanj.mybatis.domain.DepartmentMapper.DepartmentMap">            <!-- <id column="dept_id" property="id" /> -->            <!-- <result column="dept_name" property="name" /> -->            <!-- <result column="dept_sn" property="sn" /> -->        </association>    </resultMap>    <select id="get" parameterType="Long" resultMap="UserMap">        <!-- 此时先将department的数据一并查询出来 -->        select u.*,d.name dept_name,d.sn dept_sn from t_user u LEFT JOIN        t_department d on u.dept_id=d.id where u.id = #{cc}    </select>    <select id="list" resultMap="UserMap">        select u.*,d.name dept_name,d.sn        dept_sn from t_user u LEFT JOIN t_department d on u.dept_id=d.id    </select></mapper>

Department对User是一对多

-----------------department的mapper映射配置文件-----------------------<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.tabchanj.mybatis.domain.DepartmentMapper">    <resultMap type="Department" id="DepartmentMap">        <id column="id" property="id" />        <result column="name" property="name" />        <result column="sn" property="sn" />        <!--         property:指明本类users属性        ofType:指明users集合中装的时User类型的数据        select:该查询语句还是使用的是user的mapper映射配置文件中的查询语句,从路径就可以看出        column:指明该查询语句中的参数时本类中的id列的值         -->        <collection property="users" ofType="User"            select="com.tabchanj.mybatis.domain.UserMapper.getByDeptId" column="id">        </collection>    </resultMap>    <select id="get" parameterType="Long" resultMap="DepartmentMap">        select * from        t_department where id = #{id}    </select>    <select id="list" resultMap="DepartmentMap">        select * from t_department    </select></mapper>

-------User的mapper映射配置文件(只保留了id="getByDeptId"的sql查询语句)--------------------

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.tabchanj.mybatis.domain.UserMapper">    <resultMap type="com.tabchanj.mybatis.domain.User" id="UserMap">        <!-- User的基本属性 -->        <id property="id" column="id" />        <result property="name" column="name" />       </resultMap><!-- 该语句在department的mapper映射配置文件中被引用--> <select id="getByDeptId" parameterType="Long" resultMap="UserMap">        select * from t_user where dept_id=#{id}    </select></mapper>

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