MyBatis一对多查询，association实现

红太狼 2022-08-31 13:20 179阅读 0赞

## 实体类 ##

*  Dept.java

public class Dept { 
    	private int deptno;
    	private String dname;
    	private String loc;
    	private List<Emp> emps;
    	//…… getter/setter方法
    }

*  Emp.java

public class Emp { 
        private Integer empno;
        private String ename;
        private String job;
        private Integer mgr;
        private LocalDate hiredate;
        private BigDecimal sal;
        private BigDecimal comm;
        private Dept dept;  // 多对一：在多的一方添加一
    	//getter/setter方法、默认构造方法、去除dept属性的全参构造方法及toString()方法
    }

## EmpMapper.java ##

@Mapper
    public interface EmpMapper {
        // 查询指定编号员工的详细信息，包括所在部门的详细信息
        Emp getEmp(@Param("empno") Integer empno);
    }

## EmpMapper.xml ##

<mapper namespace="com.hc.mapper.EmpMapper">
        <resultMap id="BaseResultMap" type="com.hc.domain.Emp">
            <id column="empno" jdbcType="INTEGER" property="empno"/>
            <result column="ename" jdbcType="VARCHAR" property="ename"/>
            <result column="job" jdbcType="VARCHAR" property="job"/>
            <result column="mgr" jdbcType="INTEGER" property="mgr"/>
            <result column="hiredate" jdbcType="DATE" property="hiredate"/>
            <result column="sal" jdbcType="DECIMAL" property="sal"/>
            <result column="comm" jdbcType="DECIMAL" property="comm"/>
            
            <association property="dept" javaType="com.hc.domain.Dept">
                <id column="dno" property="deptno"/>
                <result column="dname" property="dname"/>
                <result column="loc" property="loc"/>
            </association>
        </resultMap>
        <select id="getEmp" resultMap="BaseResultMap2">
            select empno, ename, job, mgr, hiredate,sal, comm,
                   dept.deptno dno, dept.dname, dept.loc
            from tb_emp emp
                         left join tb_dept dept on emp.deptno = dept.deptno
            where empno = #{empno}
        </select>
    </mapper>

## 测试代码 ##

@SpringBootTest
    public class EmpMapperTest { 
        @Resource
        private EmpMapper empMapper;
        @Test
        void getEmp(){ 
            Emp emp = empMapper.getEmp(7788);
            System.out.println(emp);
        }
    }