spring boot data@Query to DTO

Question

我想将查询的结果分配给DTO对象。DTO如下所示：

@Getter
@Setter
@NoArgsConstructor
public class Metric {
    private int share;
    private int shareholder;

    public Metric(int share, int shareholder) {
        this.share = share;
        this.shareholder = shareholder;
    }
            
}

查询如下所示：

@RepositoryRestResource(collectionResourceRel = "shareholders", path = "shareholders")
public interface ShareholderRepository extends PagingAndSortingRepository<Shareholder, Integer> {
    @Query(value = "SELECT new com.company.shareholders.sh.Metric(SUM(s.no_of_shares),COUNT(*)) FROM shareholders s WHERE s.attend=true")
    Metric getMetrics();
}

然而，这没有起作用，因为我得到了以下例外情况：

Caused by:org.hibernate.QueryException: could not resolve property: no_of_shares of:com.company.shareholders.sh.Shareholder[SELECT new com.company.shareholders.sh.Metric(SUM(s.no_of_shares),COUNT(*)) FROM com.company.shareholders.sh.Shareholder s WHERE s.attend=true]

Answer 1

在我的项目中，我使用了如下所示的投影：

@Repository
public interface PeopleRepository extends JpaRepository<People, Long> {
    
    @Query(value = "SELECT p.name AS name, COUNT(dp.people_id) AS count " +
                   "FROM people p INNER JOIN dream_people dp " +
                   "ON p.id = dp.people_id " +
                   "WHERE p.user_id = :userId " +
                   "GROUP BY dp.people_id " +
                   "ORDER BY p.name", nativeQuery = true)
    List<PeopleDTO> findByPeopleAndCountByUserId(@Param("userId") Long userId);
    
    @Query(value = "SELECT p.name AS name, COUNT(dp.people_id) AS count " +
                   "FROM people p INNER JOIN dream_people dp " +
                   "ON p.id = dp.people_id " +
                   "WHERE p.user_id = :userId " +
                   "GROUP BY dp.people_id " +
                   "ORDER BY p.name", nativeQuery = true)
    Page<PeopleDTO> findByPeopleAndCountByUserId(@Param("userId") Long userId, Pageable pageable);
    
    }

结果投影到的接口：

public interface PeopleDTO {    
    String getName();
    Long getCount();    
}

投影界面中的字段必须与此实体中的字段匹配。否则字段映射可能中断。

@Query(value = "SELECT new " + 
               "SUM(s.no_of_shares) AS sum,COUNT(*) AS count FROM " +
               "shareholders s WHERE s.attend=true", nativeQuery = true)
MetricDTO getMetrics();

并创建interfaceMetricdTo，如下所示：

public interface MetricDTO {
    Integer getSum();    
    Long getCount();    
}

还要确保getSum()和getCount()的返回类型是正确的，这可能基于非数据库而有所不同。