Question

我正在努力应对JPA Criteria API子查询关联。从复杂的查询中，我用这个简单的案例复制了我的问题：

@Entity
public class Person {

    @Id
    Long id;

    String name;

    @ManyToMany
    Set<Person> relatives;

}

CriteriaQuery<Long> criteriaQuery = criteriaBuilder.createQuery(Long.class);

Root<Person> from = criteriaQuery.from(Person.class);

Subquery<Long> subquery = criteriaQuery.subquery(Long.class);

SetJoin<Person, Person> correlate = subquery.correlate(from.joinSet("relatives"));

Subquery<Long> where = subquery.select(criteriaBuilder.count(correlate)).where(criteriaBuilder.equal(correlate.get("name"), "Giovanni"));

criteriaQuery = criteriaQuery.select(criteriaBuilder.count(from)).where(criteriaBuilder.greaterThan(where, 0L));

entityManager.createQuery(criteriaQuery).getSingleResult();

无法生成带有空from ...子句的子查询：

select count(generatedAlias0)
from Person as generatedAlias0
inner join generatedAlias0.relatives as generatedAlias1
where (
    select count(generatedAlias1)
    from
    where generatedAlias1.name=:param0
) > 0L

我认为correlate会设置正确的from。我错过了什么？

Answer 1

我解决了这个问题：问题是用作correlate参数的错误表达式。应该在原始 From表达式上进行关联，而不是目标;即。

CriteriaQuery<Long> criteriaQuery = criteriaBuilder.createQuery(Long.class);

Root<Person> from = criteriaQuery.from(Person.class);

Subquery<Long> subquery = criteriaQuery.subquery(Long.class);

Root<Person> correlate = subquery.correlate(from);
// Instead of SetJoin<Person, Person> correlate = subquery.correlate(from.joinSet("relatives"));

Subquery<Long> where = subquery.select(criteriaBuilder.count(correlate)).where(
    criteriaBuilder.equal(correlate.joinSet("relatives").get("name"), "Giovanni")
                          /* ^^^ instead of correlate.get("name") */
);

criteriaQuery = criteriaQuery.select(criteriaBuilder.count(from)).where(criteriaBuilder.greaterThan(where, 0L));

entityManager.createQuery(criteriaQuery).getSingleResult();

缺少＆＃34;来自＆＃34;在JPA相关子查询中

1 个答案: