如何用JPA规范选择字段子集[重复]

Question

public class Referral {
 
   long id;
   Date createdDate;

   B anotherObject1;
   C anotherObject2;

   ..... etc
}

public Specification<ClinAssistReferral> getSpecification(Contact currentContact) {
    return (itemRoot, query, criteriaBuilder) -> {
      
        List<Predicate> finalQueries = new ArrayList<>();
        finalQueries.add(criteriaBuilder.equal(itemRoot.get("anotherObject1").get("field1"), currentContact.getId()));
        finalQueries.add(criteriaBuilder.equal(itemRoot.get("anotherObject2").get("field5"), currentContact.getJeta()));

        return   criteriaBuilder.and(finalQueries.toArray(new Predicate[0]));
    };
}

Specification< Referral > spec = getSpecification(currentContact);
List<Referral> refs = repository.findAll(spec, pageable);

@Override
@NonNull
List<Referral> findAll(@Param("spec") Specification<Referral> spec);

我尝试通过添加以下内容来更改规范创建方法：

return (itemRoot, query, criteriaBuilder) -> {
        List<Selection<?>> selectionList = new ArrayList<>();
        selectionList.add(itemRoot.get("id"));
        selectionList.add(itemRoot.get("createdDate"));
        query.multiselect(selectionList);

        List<Predicate> finalQueries = new ArrayList<>();
        finalQueries.add(criteriaBuilder.equal(itemRoot.get("anotherObject1").get("field1"), currentContact.getId()));
        finalQueries.add(criteriaBuilder.equal(itemRoot.get("anotherObject2").get("field5"), currentContact.getJeta()));

        return   criteriaBuilder.and(finalQueries.toArray(new Predicate[0]));
    };
}

它没有帮助。似乎它把整个对象都拉起来了。或者可能是我没有以正确的方式使用查询。multiselect。我能找人帮忙吗？

Answer 1

当必须使用规范中的其他字段时，是否有一种方法可以用字段的子列表拉出对象？

显然还没有。您可以在这里阅读https://stackoverflow.com/a/42049307/12854146

如果需要，您可以使用标准jpa来实现您需要的功能

@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
private static class ReferralDTO {
    private Long id;
    private Date createdDate;
}

private List<ReferralDTO> findAllByCurrentContact(Contact currentContact) {
    CriteriaBuilder builder = entityManager.getCriteriaBuilder();
    CriteriaQuery<ReferralDTO> criteria = builder.createQuery(ReferralDTO.class);
    Root<Referral> referral = criteria.from(Referral.class);

    //projection
    criteria.select(builder.construct(ReferralDTO.class, referral.get("id"), referral.get("createdDate")));

    //where
    criteria.where(
            builder.equal(referral.get("anotherObject1").get("field1"), currentContact.getId()),
            builder.equal(referral.get("anotherObject2").get("field5"), currentContact.getJeta()));
    
    //if you need sorting invoke criteria.orderBy()

    TypedQuery<ReferralDTO> query = entityManager.createQuery(criteria);
    //if you need pagination invoke query.setFirstResult and query.setMaxResults

    return query.getResultList();
}