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
attr5
得到 Specification
的总和,我该怎么做?
提前谢谢您。
经过一番研究,解决方案如下:
创建接口:
interface MyRepositoryCustom {
<S extends Number> S sum(Specification<MyEntity> spec, Class<S> resultType, String fieldName);
}
实施:
@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;
}
}
主存储库应该同时扩展
JpaRepository
和 MyRepositoryCustom
:
@Repository
interface MyEntityRepository extends JpaRepository<MyEntity, Long>, MyRepositoryCustom {
}
完成之前的解决方案:
如果我们想要对关联实体的属性求和,例如对 attr6 求和:
class MyEntity {
Long id;
MyEntityDetail detail;
String attr1;
String attr2;
String attr3;
String attr4;
Double attr5;
}
class MyEntityDetail {
Long id;
Double attr6;
}
调用先前实现的示例:
Double result = myRepository.sum(getSpecification(filtre), Double.class, "detail.attr6");
我们收到错误:
“无法在此找到具有给定名称 [detail.attr6] 的属性 托管类型”
要解决此错误,我们需要迭代关联(与 MyEntity 关联的 MyEntityDetail)。 因此,之前的实现变成(见评论):
@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);
// Resolve associate entities, replace original line : query.select(builder.sum(root.get(fieldName).as(resultType)));
Path<S> fieldPath;
if (fieldName.contains(".")) {
String[] parts = fieldName.split("\\.");
fieldPath = root.get(parts[0]);
for (int i = 1; i < parts.length; i++) {
fieldPath = fieldPath.get(parts[i]);
}
query.select(builder.sum(fieldPath.as(resultType)));
} else {
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;
}
}