准备
数据库表
员工表（t_employee）
部门表（t_department）
表所对应的类
员工 t_employee
部门 t_department
方式一（collection）
以通过部门id，查询部门信息，以及部门中所有员工信息为例。
接口
public interface DepartmentMapper { //通过部门的did查询部门所有信息 Department selectDepartment(@Param("did")Integer did); }
映射文件
<?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"><!--约束，约束不同xml中所写的标签也不同--> <mapper namespace="com.xxx.mapper.DepartmentMapper"><!--接口--> <resultMap id="deptMap" type="com.xxx.pojo.Department"> <id property="did" column="did"></id> <result property="dname" column="dname"></result> <collection property="emp" ofType="com.xxx.pojo.Employee"> <id property="eid" column="eid"></id> <result property="ename" column="ename"></result> <result property="age" column="age"></result> <result property="sex" column="sex"></result> </collection> </resultMap> <!-- //通过部门的did查询部门所有信息 Department selectDepartment(@Param("did")Integer did);--> <select id="selectDepartment" resultMap="deptMap"> select t_department.*,t_employee.* from t_department left join t_employee on t_department.did=t_employee.did where t_department.did=#{did} </select> </mapper>
测试
DepartmentMapper mapper = sqlSession.getMapper(DepartmentMapper.class); //查询部门did=2的所有信息 Department department = mapper.selectDepartment(2); System.out.println(department);
Department{did=2, dname='部门2', emp=[Employee{eid=4, ename='翠花', age=19, sex='女', dept=null}, Employee{eid=3, ename='小红', age=20, sex='女', dept=null}]}
方式二（分步查询）
以通过部门id，查询部门信息，以及部门中所有员工信息为例。
第一步接口
public interface DepartmentMapper { //通过部门的did查询部门所有信息 Department selectDepartment(@Param("did")Integer did); }
第二步接口
public interface EmployeeMapper { //通过员工部门的did查询员工的所有信息 Employee selectEmployee(@Param("did")Integer did); }
第一步映射文件
<?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"><!--约束，约束不同xml中所写的标签也不同--> <mapper namespace="com.xxx.mapper.DepartmentMapper"><!--接口--> <resultMap id="deptMap" type="com.xxx.pojo.Department"> <id property="did" column="did"></id> <result property="dname" column="dname"></result> <!--此处的select中写的是第二步接口中的方法的全路径，colum中写的是第一步查出的那个数据作为第二步的参数--> <collection property="emp" select="com.xxx.mapper.EmployeeMapper.selectEmployee" column="did"></collection> </resultMap> <!-- //通过部门的did查询部门所有信息 Department selectDepartment(@Param("did")Integer did);--> <select id="selectDepartment" resultMap="deptMap"> select * from t_department where did=#{did} </select> </mapper>
第二步映射文件
<?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"><!--约束，约束不同xml中所写的标签也不同--> <mapper namespace="com.xxx.mapper.EmployeeMapper"><!--接口--> <select id="selectEmployee" resultType="com.xxx.pojo.Employee"> select * from t_employee where did=#{did} </select> </mapper>
测试
DepartmentMapper mapper = sqlSession.getMapper(DepartmentMapper.class); //查询部门did=2的所有信息 Department department = mapper.selectDepartment(2); System.out.println(department);
Department{did=2, dname='部门2', emp=[Employee{eid=4, ename='翠花', age=19, sex='女', dept=null}, Employee{eid=3, ename='小红', age=20, sex='女', dept=null}]}
