hibernate - JPA 相关子查询中缺少 "from"

Question

我正在努力处理 JPA Criteria API 子查询关联。从一个复杂的查询中，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

我会解决这个问题:问题是错误的表达式用作 correlate 参数。关联应该在 originat From 表达式上完成，而不是在目标上；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();