JPA：使用投影返回自定义对象

Question

我在SponsorRepository中有此代码，扩展了JpaRepository<Sponsor, Long> ...

@Query(value = "SELECT s.fundraiser_name, d.amount_in_pence/100" +
            " FROM sponsor_form s INNER JOIN donation d ON s.id = d.sponsor_form_id " +
            "WHERE d.charity_id = :charityId ORDER BY d.amount_in_pence*100 DESC LIMIT 5", nativeQuery =
            true)
public List<Sponsor> findTopFiveSponsors(@Param("charityId") Long charityId);

问题是，在运行服务器时，它给我一个错误，提示未找到该ID。我对此进行了研究，发现即使查询本身返回的是筹款人的名称和金额，我仍在使函数返回发起人的列表。而且，JPA无法将此映射到赞助商列表中。建议我使用JPA投影。我需要采取哪些步骤？投影是解决方案还是RestController？

Answer 1

为结果元组创建新的保护界面：

public interface SponsorProjection {    
    String getName();
    Long getAmount();
}

然后添加别名并更改返回类型：

@Query(value = "SELECT s.fundraiser_name as name, d.amount_in_pence/100 as amount " +
               "FROM sponsor_form s INNER JOIN donation d ON s.id = d.sponsor_form_id " +
               "WHERE d.charity_id = :charityId " +
               "ORDER BY d.amount_in_pence * 100 DESC LIMIT 5", nativeQuery = true)
public List<SponsorProjection> findTopFiveSponsors(@Param("charityId") Long charityId);

您的控制器将如下所示：

@RestController
public class SponsorController {

    @Autowired
    private SponsorRepository repo;

    @GetMapping(path = "/findTopFiveSponsors")
    public ResponseEntity<?> get(@Param("charityId") Long charityId) {
        return ResponseEntity.ok(repo.findTopFiveSponsors(charityId));
    }

}