hibernate - 如何在 jpa 标准中执行 JOIN FETCH

Question

我正在尝试将下面的查询转换为标准 api。

SELECT er from ereturn er JOIN FETCH product_item pi ON pi.ereturn_id = er.id WHERE pi.status = "RECEIVED"

对于这样的事情:

CriteriaBuilder builder = em.getCriteriaBuilder();

CriteriaQuery<Ereturn> criteria = builder.createQuery( Ereturn.class );

Root<Ereturn> er = criteria.from(Ereturn.class);
Join<Ereturn, ProductItem> productItemJoin = er.join("productItems", JoinType.LEFT);
Fetch<Ereturn, ProductItem> productItemFetch = er.fetch("productItems", JoinType.LEFT);

List<Predicate> predicates = new ArrayList<>();

predicates.add(builder.equal( productItemJoin.get( "status" ), "RECEIVED"));

criteria.where(
        builder.and(predicates.toArray(new Predicate[predicates.size()]))
);

List<Ereturn> ers = em.createQuery( criteria )
    .getResultList();

问题是 hibernate 生成这个查询:

select
ereturn0_.id as ...
...
productite6_.id as ...
...
from
ereturn ereturn0_ 
join
product_item productite1_ 
on ereturn0_.id = productite1_.ereturn 
join
product_item productite6_ 
on ereturn0_.id = productite6_.ereturn
where
productite1_.status='RECEIVED';

问题:我怎么能告诉 hibernate 在从两个表(ereturn 和 productItem)中获取字段时只生成 1 个连接的查询？

Answer 1

确实这是一个问题，但您的答案显示了两个额外的表格，并且不是正确答案。尝试这个:

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Ereturn> q = cb.createQuery(Ereturn.class);
Root<Ereturn> r = q.from(Ereturn.class);
r.fetch("productItem", JoinType.LEFT);
// here join with the root instead of the fetch
// casting the fetch to the join could cause portability problems
// plus, not nice
q.where(cb.equal(r.get("productItem").get("status"), "received"));
Ereturn ereturn= em.createQuery(q).getSingleResult();

这使

select ereturn0_.id as id1_0_0_, productite1_.id as id1_1_1_, ereturn0_.parentEreturn_id as parentCo2_0_0_, ereturn0_.productItem_id as productI3_0_0_, productite1_.status as status2_1_1_ 
from Ereturn ereturn0_ 
left outer join ProductItem productite1_ on ereturn0_.productItem_id=productite1_.id 
where productite1_.status=?

见 JPA 2 Criteria Fetch Path Navigation在答案中再往下一点。