JPA：使用投影返回自定義 object

Question

我在SponsorRepository中有這段代碼，它擴展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);

問題是，在運行服務器時，它給了我一個錯誤，說找不到 id。 我對此進行了研究，發現我正在讓 function 返回贊助商列表，即使查詢本身返回籌款人名稱和金額。 此外，JPA 不能將 map 列入贊助商名單。 有人建議我使用 JPA 投影。 我需要采取哪些步驟才能這樣做？ 投影是解決方案還是RestController ？

Answer 1

為您的結果元組創建新的保護接口：

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

然后添加別名並更改返回類型：

@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 controller 將如下所示：

@RestController
public class SponsorController {

    @Autowired
    private SponsorRepository repo;

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

}