SpringBoot+MybatisPlus实现关联表查询

1.说明

最近写代码用到了mybatisPlus涉及到关联表查询。需求是这样的：
我有一个专业表major其中有个字段是所属院系dept_id，我需要通过这个dept_id关联院系表department的ID去获取院系的名称。
例如：经济管理学院。

实现效果：

2.实现步骤

2.1 现有实体类

• 院系实体

```java
@Data
@EqualsAndHashCode(callSuper = false)
@Accessors(chain = true)
@TableName("tb_department")
@ApiModel(value="Department对象", description="院系")
public class Department implements Serializable {

    private static final long serialVersionUID = 1L;

    @ApiModelProperty(value = "院系ID")
    @TableId(value = "id", type = IdType.AUTO)
    private Long id;

    @ApiModelProperty(value = "院系代码")
    private String deptNo;

    @ApiModelProperty(value = "院系名称")
    private String deptName;

    @ApiModelProperty(value = "院系位置")
    private String deptLocation;

    @ApiModelProperty(value = "备注")
    private String deptRemark;

    @ApiModelProperty(value = "创建时间")
    @TableField(fill = FieldFill.INSERT)
    private Date createTime;

    @ApiModelProperty(value = "更新时间")
    @TableField(fill = FieldFill.INSERT_UPDATE)
    private Date updateTime;


}

• 专业实体

@Data
@EqualsAndHashCode(callSuper = false)
@Accessors(chain = true)
@TableName("tb_major")
@ApiModel(value="Major对象", description="专业")
public class Major implements Serializable {

    private static final long serialVersionUID = 1L;

    @ApiModelProperty(value = "专业ID")
    @TableId(value = "id", type = IdType.AUTO)
    private Long id;

    @ApiModelProperty(value = "专业代码")
    private String majorNo;

    @ApiModelProperty(value = "专业名称")
    private String majorName;

    @ApiModelProperty(value = "所属学院")
    private Long deptId;

    @ApiModelProperty(value = "备注")
    private String majorRemark;

    @ApiModelProperty(value = "创建时间")
    @TableField(fill = FieldFill.INSERT)
    private Date createTime;

    @ApiModelProperty(value = "更新时间")
    @TableField(fill = FieldFill.INSERT_UPDATE)
    private Date updateTime;


}

2.2 创建vo对象

• MajorVO 前端列表展示用

@Data
@ApiModel(value = "MajorVO", description = "展示用专业信息")
public class MajorVO implements Serializable {
    private static final long serialVersionUID = 1L;

    @ApiModelProperty(value = "专业ID")
    private Long id;

    @ApiModelProperty(value = "专业代码")
    private String majorNo;

    @ApiModelProperty(value = "专业名称")
    private String majorName;

    @ApiModelProperty(value = "所属院系ID")
    @TableField("dept_id")
    private Long deptId;

    @ApiModelProperty(value = "所属院系")
    private String deptName;

    @ApiModelProperty(value = "备注")
    private String majorRemark;

    @ApiModelProperty(value = "创建时间")
    private Date createTime;
}

2.3 修改MajorMapper

public interface MajorMapper extends BaseMapper<Major> {
    /**
     *
     * @param page 前端传入
     * @return
     */
    @Select("SELECT m.*,d.`dept_name` FROM tb_major m,tb_department d WHERE m.dept_id=d.id")
    List<MajorVO> selectMajorList(Page page);

}

2.4 修改MajorService

public interface MajorService extends IService<Major> {
    void pageQuery(Page<MajorVO> pageParam);

}

@Service
public class MajorServiceImpl extends ServiceImpl<MajorMapper, Major> implements MajorService {

    @Override
    public void pageQuery(Page<MajorVO> page) {
         List<MajorVO> records = baseMapper.selectMajorList(page);
         page.setRecords(records);
         page.setTotal(records.size());

    }
}

2.5 修改controller

@ApiOperation(value = "专业分页列表")
    @GetMapping("{page}/{limit}")
    public Result pageQuery(
            @ApiParam(name = "page", value = "当前页码", required = true)
            @PathVariable Long page,
            @ApiParam(name = "limit", value = "每页记录数", required = true)
            @PathVariable Long limit){

        Page<MajorVO> pageParam = new Page<>(page, limit);
        majorService.pageQuery(pageParam);

        return  Result.ok().data("total", pageParam.getTotal()).data("rows", pageParam.getRecords());
    }

3.swagger测试