持久性实体不能为空 [英] Persistence Entity must not be null

问题描述

使用以下代码我收到错误持久性实体不能为空.可能是什么错误.

with following code I am getting error Persistence entity must not be null. what could be the mistake.

public interface DistrictRepo extends PagingAndSortingRepository<District, Integer> {

    @Query(
            "select d.districtId, d.districtName from District d where d.districtId in (:districtIds) group by d.districtId"
    )
    @RestResource(path="byList")
    List<Object[]> byList(@Param("districtIds") List<Integer> districtIds);
}

推荐答案

如果您打算采用搜索"方法，请使用以下方法:

If you are going to make a "search" method, use this approach:

@Projection(name = "idAndName", types = {District.class})
public interface IdAndName {
    Integer getId();
    String getName();
}

@RestResource(path="byIds", rel="byIds")
@Query("select d from District d where d.districtId in (:districtIds)")
List<District> findByIds(@Param("ids") Integer... ids);

然后使用这个网址:

http://localhost:8080/api/districts/search/byIds?ids=1,2,3&projection=idAndName

关于投影的更多信息

如果您需要使用带有返回 DTO 的分组和聚合的复杂查询，则不能使用搜索"方法.相反，您必须实施 自定义控制器，例如:

If you need to use complex queries with grouping and aggregation that return DTOs you can not use "search" methods. Instead you have to implement custom controller, for example:

@RepositoryRestController
@RequestMapping("/districts")
public class DistrictController {

    @Autoware
    private DistrictRepo repo;

    @GetMapping("/report")
    public ResponseEntity<?> report(@RequestParam(value = "ids") Integer... ids) {
        List<Dto> dtos = repo.getDtosByIds(ids);
        return ResponseEntity.ok(new Resources<>(dtos));
    }
}

其中 Dto 是这样的:

@Data // This is Lombok annotation (https://projectlombok.org/)
@Relation(value = "district", collectionRelation = "districts")
public class Dto {

    private final Integer id;
    private final String name;
}

像这样的 repo 方法:

And something like this the repo method:

public interface DistrictRepo extends PagingAndSortingRepository<District, Integer> {

    @Query("select new ...Dto(d.districtId, d.districtName) from District d where d.districtId in (:districtIds) group by d.districtId")
    @RestResource(path="byList", rel="byList")
    List<Dto> getDtosByIds(@Param("ids") Integer... ids);
}

更多信息.

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