代码实现

entity、mapper、service、controller 使用了 MyBatisPlus 的代码生成器，自动生成大部分基础的代码，操作方法见之前的文章：

在 SpringBoot 中引入 MyBatisPlus 之 常规操作

1.实体

① Question

// import 省略

@TableName("t_question")
public class Question implements Serializable {

  private static final long serialVersionUID = 1L;

  @ApiModelProperty(value = "问答主键id")
  @TableId(value = "id", type = IdType.AUTO)
  private Integer id;

  @ApiModelProperty(value = "学生外键id")
  @TableField("student_id")
  private Integer studentId;

  @ApiModelProperty(value = "问题内容")
  private String content;

  @ApiModelProperty(value = "问题发布时间，发布的时候后台自动生成")
  private Date date;

  @ApiModelProperty(value = "问题悬赏的积分")
  private Integer value;

	// getter、setter 省略
}

② Student

// import 省略

@TableName("t_student")
public class Student implements Serializable {

  private static final long serialVersionUID = 1L;

  @ApiModelProperty(value = "学生主键id")
  @TableId(value = "id", type = IdType.AUTO)
  private Integer id;

  @ApiModelProperty(value = "学生名称")
  private String name;

  @ApiModelProperty(value = "学生密码")
  private String password;

  @ApiModelProperty(value = "学生积分数")
  private Integer points;

  @ApiModelProperty(value = "学生邮件地址")
  private String email;

  @ApiModelProperty(value = "学生手机号码")
  private String phone;

  @ApiModelProperty(value = "学生学号")
  private String num;

  @ApiModelProperty(value = "学生真实姓名")
  @TableField("true_name")
  private String trueName;

	// getter、setter 省略
}

2.mapper

① StudentMapper

// import 省略
public interface StudentMapper extends BaseMapper {
}

② QuestionMapper

// import 省略
public interface QuestionMapper extends BaseMapper {
  /**
   *
   * @param page 翻页对象，可以作为 xml 参数直接使用，传递参数 Page 即自动分页
   * @return
   */
  @Select("SELECT t_question.*,t_student.`name` FROM t_question,t_student WHERE t_question.student_id=t_student.id")
  List getQuestionStudent(Pagination page);

}

3、service

① StudentService

// import 省略
public interface StudentService extends IService {
}

② QuestionService

// import 省略
public interface QuestionService extends IService {

  Page getQuestionStudent(Page page);

}

4、serviceImpl

① StudentServiceImpl

// import 省略
@Service
public class StudentServiceImpl extends ServiceImpl implements StudentService {

}

② QuestionServiceImpl

// 省略 import

@Service
public class QuestionServiceImpl extends ServiceImpl implements QuestionService {

  @Override
  public Page getQuestionStudent(Page page) {
    return page.setRecords(this.baseMapper.getQuestionStudent(page));
  }

}

5、controller

// 省略 import

@RestController
@RequestMapping("/common")
@EnableSwagger2
public class CommonController {

  @Autowired
  QuestionService questionService;

  @Autowired
  StudentService studentService;

  @GetMapping("/getAllQuestionByPage/{page}/{size}")
  public Map getAllQuestionByPage(@PathVariable Integer page, @PathVariable Integer size) {
    Map map = new HashMap<>();
    Page questionPage = questionService.selectPage(new Page<>(page, size));
    if (questionPage.getRecords().size() == 0) {
      map.put("code", 400);
    } else {
      map.put("code", 200);
      map.put("data", questionPage);
    }
    return map;
  }

  @GetMapping("/getAllQuestionWithStudentByPage/{page}/{size}")
  public Map getAllQuestionWithStudentByPage(@PathVariable Integer page, @PathVariable Integer size) {
    Map map = new HashMap<>();
    Page questionStudent = questionService.getQuestionStudent(new Page<>(page, size));
    if (questionStudent.getRecords().size() == 0) {
      map.put("code", 400);
    } else {
      map.put("code", 200);
      map.put("data", questionStudent);
    }
    return map;
  }

}

6、MyBatisPlus 配置

// 省略 import

@EnableTransactionManagement
@Configuration
@MapperScan("com.cun.app.mapper")
public class MybatisPlusConfig {

  /**
   * 分页插件
   */
  @Bean
  public PaginationInterceptor paginationInterceptor() {
    return new PaginationInterceptor();
  }

  /**
   * 打印 sql
   */
  @Bean
  public PerformanceInterceptor performanceInterceptor() {
    PerformanceInterceptor performanceInterceptor = new PerformanceInterceptor();
    //格式化sql语句
    Properties properties = new Properties();
    properties.setProperty("format", "true");
    performanceInterceptor.setProperties(properties);
    return performanceInterceptor;
  }
}

7、关联查询 VO 对象

// import 省略

public class QuestionStudentVO implements Serializable {

  @ApiModelProperty(value = "问答主键id")
  @TableId(value = "id", type = IdType.AUTO)
  private Integer id;

  @ApiModelProperty(value = "学生外键id")
  @TableField("student_id")
  private Integer studentId;

  private String name;

  @ApiModelProperty(value = "问题内容")
  private String content;

  @ApiModelProperty(value = "问题发布时间，发布的时候后台自动生成")
  private Date date;

  @ApiModelProperty(value = "问题悬赏的积分")
  private Integer value;

	// getter、setter 省略

五、测试接口

1、没有关联的分页查询接口

http://localhost/common/getAllQuestionByPage/1/2

① json 输出

{
 "code": 200,
 "data": {
  "total": 10,
  "size": 2,
  "current": 1,
  "records": [
   {
    "id": 1,
    "studentId": 3,
    "content": "唐代，渝州城里，有一个性格开朗、乐观的小伙子，名叫景天。",
    "date": 1534497561000,
    "value": 5
   },
   {
    "id": 2,
    "studentId": 1,
    "content": "雪见从小父母双亡，由爷爷唐坤抚养成人。",
    "date": 1533201716000,
    "value": 20
   }
  ],
  "pages": 5
 }
}

② sql 执行

2、多表关联、分页查询接口

http://localhost/common/getAllQuestionWithStudentByPage/1/2

① json 输出

{
 "code": 200,
 "data": {
  "total": 10,
  "size": 2,
  "current": 1,
  "records": [
   {
    "id": 1,
    "studentId": 3,
    "name": "vv",
    "content": "唐代，渝州城里，有一个性格开朗、乐观的小伙子，名叫景天。",
    "date": 1534497561000,
    "value": 5
   },
   {
    "id": 2,
    "studentId": 1,
    "name": "cun",
    "content": "雪见从小父母双亡，由爷爷唐坤抚养成人。",
    "date": 1533201716000,
    "value": 20
   }
  ],
  "pages": 5
 }
}

② sql 执行

六、小结

写本文的原因：

①网上有做法不合时宜的文章（自定义page类、配置版）②官方文档使用的是配置版的，笔者采用注解版的