JPA 自定义返回字段映射

 实体类：User.java

@Data
@Accessors(chain = true)
@EqualsAndHashCode(callSuper = true)
@Entity
@Table(name = "user")
public class User extends AbstractEntity {

    @Column(unique = true)
    private String username;

    private String password;

    private String nickname;

    private String email;

    @Column(name = "org_id")
    private Long orgId;

    @Column(name = "org_name")
    private String orgName;
}

DTO类：UserDTO.java

import lombok.Value;

/**
 * @author wu qilong
 * @date 2019/4/11
 * @Description: 自定义返回值，字段名称要和User实体类中的一致，加上[email protected]注解。
 */
@Value
public class UserDTO {

    private String username;

    private String nickname;

    private String email;
}

repository类：UserRepository.java

/**
 * @author Wu Qilong
 * @date 2019/4/11
 * @Description:
 */
public interface UserRepository extends JpaRepository<User, Long> {

    /**
     * 用户名查询
     *
     * @param username
     * @return
     */
    Optional<User> findByUsername(String username);


    /**
     * 用户名查询
     * @param username
     * @return
     */
    <T> Optional<T> findByUsername(String username, Class<T> type);
}

  测试：

@RunWith(SpringRunner.class)
@SpringBootTest
public class UoServerApplicationTests {

    @Autowired
    UserRepository userRepository;

    @Test
    public void contextLoads() {
        UserDTO userDTO = userRepository.findByUsername("hezhigang", UserDTO.class).get();
        Console.log(userDTO);
    }
}

• 注意：返回的DTO中属性名称需要和实体类中字段名一致，且加上lombok包中的@Value注解，这种方式对于只需要返回表中部分的字段很方便，如果需要自定义返回字段名称，可以参考以下方法：

• 需求：统计注册人数

1. 定义一个返回对象
2. 使用@Query(value = "select new com.wd.cloud.uoserver.dto.TjVO(u.orgId ,count(u.orgId)) from User u group by orgId")进行查询。

@Value
public class TjVO {

    Long orgId;

    Long registerCount;
}

/**
     * 按机构统计注册人数
     * @param pageable
     * @return
     */
    @Query(value = "select new com.wd.cloud.uoserver.dto.TjVO(u.orgId ,count(u.orgId)) from User u group by orgId")
    Page<TjVO> tjByOrgId(Pageable pageable);

或者也可以用下面的方法：

定义一个接口，用getXxx定义返回字段。xxx需要和返回字段的别名一致。
如果不一致，可以使用org.springframework.beans.factory.annotation包中的@Value进行映射

public interface TjDTO {

    /**
     * 所属机构
     * @return
     */
    Long getOrgId();
    /**
     * 注册时间
     * @return
     */
    String getRegisterDate();

    /**
     * 注册数量
     * @return
     */
    String getRegisterCount();

    /**
     * 管理员数量 当别名与该getXXX名称不一致时，可以使用该注解调整
     * @return
     */
    @Value("#{target.adminCount}")
    Long getManagerCount();

}

repository类：UserRepository.java添加方法tjByOrgId(),返回orgId和registerCount

 /**
     * 按天统计注册人数
     * @return
     */
    @Query(value = "select DATE_FORMAT(gmt_create,\"%Y-%m-%d\") as registerDate,count(*) as registerCount from user group by registerDate",nativeQuery = true)
    List<TjDTO> tj();

    /**
     * 按机构统计注册人数
     * @param pageable  分页
     * @return
     */
    @Query(value = "select org_id as orgId,count(*) as registerCount from user group by orgId",
            countQuery = "select count(*) from user group by org_id", nativeQuery = true)
    Page<TjDTO> tjByOrgId(Pageable pageable);

测试：

@RunWith(SpringRunner.class)
@SpringBootTest
public class UoServerApplicationTests {

    @Autowired
    UserRepository userRepository;

    @Test
    public void contextLoads() {
        List<TjDTO> tjDTOList = userRepository.tj();
        tjDTOList.forEach(tjDTO -> {
            Console.log("registerDate={},registerCount={}", tjDTO.getRegisterDate(), tjDTO.getRegisterCount());
        });
    }
}

结果日志：

Hibernate: select DATE_FORMAT(gmt_create,"%Y-%m-%d") as registerDate,count(*) >as registerCount from user group by registerDate
registerDate=2019-01-28,registerCount=7393
registerDate=2019-03-07,registerCount=1

• 需求：根据机构分组，统计机构总人数和用户类型为2的人数

@Component
public class SpecBuilder {

    @PersistenceContext
    private EntityManager entityManager;

    public List<Object[]> tj(Long orgId) {
        CriteriaBuilder cb = entityManager.getCriteriaBuilder();
        CriteriaQuery<Object[]> query = cb.createQuery(Object[].class);
        Root<User> root = query.from(User.class);
        //拼接where条件
        List<Predicate> predicateList = new ArrayList<Predicate>();
        if (orgId != null) {
            predicateList.add(cb.equal(root.get("orgId"), orgId));
        }
        //加上where条件
        query.where(ArrayUtil.toArray(predicateList, Predicate.class));
        query.multiselect(root.get("orgId"),
                cb.count(root),
                cb.sum(cb.<Integer>selectCase().when(cb.equal(root.get("userType"), 2), 1).otherwise(0)));
        query.groupBy(root.get("orgId"));
        //最终sql:  select org_id,count(id),sum(case when user_type=2 then 1 else 0 end) from user where org_id=?1 group by org_id;
        TypedQuery<Object[]> typedQuery = entityManager.createQuery(query);
        return typedQuery.getResultList();
    }

}

测试：

@RunWith(SpringRunner.class)
@SpringBootTest
public class UoServerApplicationTests {

    @Autowired
    SpecBuilder specBuilder;

    @Test
    public void contextLoads() {
        List<Object[]> tjDTOList1 = specBuilder.tj(169L);
        tjDTOList1.forEach(tjDTO -> {
            Console.log("orgId={},总人数={},管理员人数={}", tjDTO[0], tjDTO[1], tjDTO[2]);
        });
    }
}

 

感谢https://www.hutool.cn/ 作者提供hutool工具包

参考：https://docs.spring.io/spring-data/jpa/docs/2.1.5.RELEASE/reference/html/#projections

https://www.jianshu.com/p/fbd157c3b4a4