Mybatis-Plus多表关联查询的使用案例解析

@Data
@EqualsAndHashCode(callSuper = false)
@TableName("dept")
public class Dept implements Serializable {
    private static final long serialVersionUID = 1L;
    @TableId
    private Integer deptno;
    private String dname;
    private String loc;
}

@Data
@EqualsAndHashCode(callSuper = false)
@TableName("emp")
public class Emp implements Serializable {
    private static final long serialVersionUID = 1L;
    @TableId("empno")
    private Integer empno;
    private String ename;
    private String job;
    private Integer mgr;
    private LocalDateTime hiredate;
    private BigDecimal sal;
    private BigDecimal comm;
    private Integer deptno;
    private Dept dept;//多表关联需要查询的数据
}

<mapper namespace="com.nb.spring_boot.api.dao.IEmpDao">
    <resultMap id="empMapper" type="com.nb.spring_boot.api.pojo.Emp">
        <association property="dept" column="deptno" select="com.nb.spring_boot.api.dao.IDeptDao.selectById"/>
    </resultMap>
    <select id="queryEmps" resultMap="empMapper">
        select * from emp
    </select>
</mapper>

Dept selectById(Integer deptno);

<select id="selectById" resultType="com.nb.spring_boot.api.pojo.Dept">
        select * from dept where deptno=#{deptno}
</select>

public interface IDeptDao extends BaseMapper<Dept> {
    Dept selectById(Integer deptno);
}

public interface IEmpDao extends BaseMapper<Emp> {
    IPage<Emp> queryEmps(IPage<Emp> page,@Param(Constants.WRAPPER) Wrapper<Emp> wrapper);
}

public interface IEmpService extends IService<Emp> {
    IPage<Emp> queryEmps(IPage<Emp> result, QueryWrapper<Emp> wrapper);
}

public class EmpServiceImpl extends ServiceImpl<IEmpDao, Emp> implements IEmpService {
    @Autowired
    IEmpDao empDao;//这里报红没事
    @Override
    public IPage<Emp> queryEmps(IPage<Emp> result, QueryWrapper<Emp> wrapper) {
        result = empDao.queryEmps(result, wrapper);
        return result;
    }
}

@RequestMapping("qemps")
IPage<Emp> queryEmps(@RequestParam(defaultValue = "1") int page,
                     @RequestParam(defaultValue = "5") int  limit){
    IPage<Emp> result = new Page<>(page, limit);
    QueryWrapper<Emp> wrapper = new QueryWrapper<>();
    wrapper.gt("sal", 1000);//查询条件，工资大于1000，其他的可以研究一下，比如eq,le,like
    return empService.queryEmps(result, wrapper);
}