JPA2CriteriaQuery在选择列表中无效，因为它既不包含在聚合函数中，也不包含在GROUP BY子句中

Question

Column 'A.PK' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

Criteria criteria = getSession().createCriteria(A.class);
criteria.setProjection(Projections.groupProperty("b"));
return criteria.list();

这不会：

Session session = getSession();
CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaQuery<A> criteriaQuery = builder.createQuery(A.class);
Root<A> root = criteriaQuery.from(A.class);
criteriaQuery.groupBy(root.get("b"));
return session.createQuery(criteriaQuery).list();

Answer 1

假设您有以下映射：

@Entity
class A {

   @ManyToOne
   private B b;
}

@Entity
class B {

  @Id
  private Long id;
}

1. 过时的条件:

Criteria criteria = getSession().createCriteria(A.class);
criteria.setProjection(Projections.groupProperty("b"));
List<B> result = criteria.list();

实际执行查询，如下所示：

select b_id
from A
group by b_id

sql prettyprint-override">select * from B where id = ?

CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaQuery<B> criteriaQuery = builder.createQuery(B.class);
Root<A> root = criteriaQuery.from(A.class);
      
Join<A, B> bJoin = root.join("b");
      
criteriaQuery.groupBy(bJoin.get("id"));
criteriaQuery.select( root.get("b") );
List<B> result = session.createQuery(criteriaQuery).list();