java - Spring Boot SUM(列)与规范

Question

我有一个实体，说:

class MyEntity {
    Long id;
    String attr1;
    String attr2;
    String attr3;
    String attr4;
    Double attr5;
}

我使用Specification来查询按属性过滤的结果，例如:

class MySpecification implements Specification<MyEntity> {
    private String attr1;
    private String attr2;
    private String attr3;
    private String attr4;

@Override
public Predicate toPredicate(Root<MyEntity> root, CriteriaQuery<?> query, CriteriaBuilder criteriaBuilder) {
    List<Predicate> restriction = new ArrayList<>();
    if (!StringUtils.isEmpty(attr1)) {
        restriction.add(criteriaBuilder.equal(root.get("attr1"), attr1));
    }
    if (!StringUtils.isEmpty(attr2)) {
        restriction.add(criteriaBuilder.equal(root.get("attr2"), attr2));
    }
    // And so on
    Predicate predicate = criteriaBuilder.disjunction();
    predicate.getExpressions().add(criteriaBuilder.and(restriction.toArray(new Predicate[restriction.size()])));
    return predicate;
    }
}

现在我想通过规范获取attr5的总和，我该怎么做？

提前谢谢您。

Answer 1

经过一番研究，解决方案如下:

创建界面:

interface MyRepositoryCustom {
    <S extends Number> S sum(Specification<MyEntity> spec, Class<S> resultType, String fieldName);
}

实现:

@Repository
class MyRepositoryCustomImpl implements MyRepositoryCustom {

    @Autowired
    private EntityManager entityManager;

    @Override
    public <S extends Number> S sum(Specification<MyEntity> spec, Class<S> resultType, String fieldName) {
        CriteriaBuilder builder = entityManager.getCriteriaBuilder();
        CriteriaQuery<S> query = builder.createQuery(resultType);
        Root<MyEntity> root = applySpecificationToCriteria(spec, query);
        query.select(builder.sum(root.get(fieldName).as(resultType)));
        TypedQuery<S> typedQuery = entityManager.createQuery(query);
        return typedQuery.getSingleResult();
    }

    protected <S> Root<MyEntity> applySpecificationToCriteria(Specification<MyEntity> spec, CriteriaQuery<S> query) {
        Root<MyEntity> root = query.from(MyEntity.class);
        if (spec == null) {
            return root;
        }
        CriteriaBuilder builder = entityManager.getCriteriaBuilder();
        Predicate predicate = spec.toPredicate(root, query, builder);
        if (predicate != null) {
            query.where(predicate);
        }
        return root;
    }
}

主存储库应扩展 JpaRepository 和 MyRepositoryCustom:

@Repository
interface MyEntityRepository extends JpaRepository<MyEntity, Long>, MyRepositoryCustom {

}