使用规范和投影的Spring JPA查询

Question

我使用spring jpa规范动态构建实体查询。

它工作完美，但是查询返回所有实体字段，这使得性能变慢。我只想获取特定的实体字段，而不是获取我不想要也不会使用的所有实体字段和依赖项。

我在网上搜索，尝试了一些场景，但没有任何不足。有人能就此提出任何解决方案吗？

提前感谢

这是我的。我正在使用spring boot 2.2.4

public class Concert {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column
    private String name;

    @Column
    private String code;

    @Column
    private double totalIncome;

    @Column            
    private double totalExpenses;

    @Column
    private double totalBudget;

    @ManyToOne(targetEntity = Orchestra.class, fetch = FetchType.EAGER, optional = false)
    @JoinColumn(name = "orchestra_id")
    private Orchestra orchestra;

    @ManyToOne(targetEntity = ConcertStatus.class, fetch = FetchType.EAGER, optional = false)
    @JoinColumn(name = "concert_status_id")
    private ConcertStatus status;

    /* other fields */

}

规格：

public class ConcertSpecification implements Specification<Concert> {

    @Override
    public Predicate toPredicate(Root<Concert> root, CriteriaQuery<?> query, CriteriaBuilder builder) {
        List<Predicate> predicates = new ArrayList<>();

        //add add criteria to predicates
        for (Criterion criteria : criteriaList) {

            /* predicates builder here */
        }

        return builder.and(predicates.toArray(new Predicate[0]));
    }
}

存储库：

public interface ConcertDao extends JpaRepository<Concert, Long>, JpaSpecificationExecutor<Concert>, PagingAndSortingRepository<Concert, Long> { }

音乐会服务：

public interface ConcertService {
    Page<Concert> findAll(@Nullable Specification<Concert> spec, Pageable pageable); 
}   

ConcertServiceImpl：

@Service(value = "concertService")
public class ConcertServiceImpl implements ConcertService {

    public Page<Concert> findAll(@Nullable Specification<Concert> spec, Pageable pageable){
        List<Concert> list = new ArrayList<>();
        concertDao.findAll(spec).iterator().forEachRemaining(list::add);
        return new PageImpl<Concert>(list);
    }
}   

Answer 1

不支持使用带有规格的投影，并且它的PR已经悬挂了五年多。