使用hibernate查询product的结果为Object, 并且不能转为Product

使用hibernate查询product的结果为Object, 并且不能转为Product。

版本：hibernater-5.2.6

错误代码：

public List<Product> findByPage(Integer cid, Integer begin, Integer countInPage) {
List<Product> products = (List<Product>) this.getHibernateTemplate().execute(new HibernateCallback<List<Product>>() {

@Override
public List<Product> doInHibernate(Session session) throws HibernateException {
Query query = session
.createQuery("from Product p join p.categorySecond cs join cs.category c where c.cid=?");
query.setFirstResult(begin);
query.setMaxResults(countInPage);
query.setParameter(0, cid);
return query.getResultList();
}
});
return products;
}

若改为

Query<Product> query = session.createQuery("from Product p join p.categorySecond cs join cs.category c where c.cid=?"
,Product.class);

则报错：Cannot create TypedQuery for query with more than one return

从stackoverflow中查得如下答案：

Without goind into details about how

Media

and

Book

should be modeled, I will at least explain why you get this exception.

You're doing:

em.createQuery(someJPQL, Media.class);

This means: create a query using

someJPQL

, and this query will return instances of the

Media

entity.

But your

JPQL

is:

SELECT m.title, b.isbn, b.authors ...

So the query does not return entities of type Media. It returns three fields, from two different entities. There is no way your JPA engine could magically create instances of Media from these 3 columns. A query would return instances of Media if it looked
like this:

select m from Media m ...

最后将代码改为如下，解决问题。

Query<Product> query = session.createQuery("select p from Product p join p.categorySecond cs join cs.category c where c.cid=?"
,Product.class);
//或
Query<Product> query = session.createQuery("select p from Product p join p.categorySecond cs join cs.category c where c.cid=?");