Java Stream 与 JPA 一对多(LAZY)关系不起作用

Question

这个问题已经有答案了:

Why does this stream return no element? (1 个回答)

已关闭 7 年前。

I have one Entity class called RCIEntity. which has a One to many mapping to its own type.

@OneToMany(mappedBy = "parent", cascade = CascadeType.ALL, fetch = FetchType.LAZY) 
@OrderBy("name ASC")           
private List<RCIEntity> children; 

public final List<RCIEntity> getChildren() {
        return children;
}

所以当我在其他地方使用这个实体时。

rciEnitity.getChildren().stream().count() // always zero.

但是如果我从中创建一个子列表，那么流就可以正常工作。

List<RCIEntity> subList = get.getChildren().subList(0,get.getChildren().size());

long count1 = subList.stream().count();//works fine 

这是一些代码...

CriteriaBuilder cb = em.getCriteriaBuilder();
        CriteriaQuery<RCIEntity> q = cb.createQuery(RCIEntity.class);
        Root<RCIEntity> from = q.from(RCIEntity.class);

        CriteriaQuery<RCIEntity> select = q.select(from);
        q.select(from).where(cb.equal(from.get(RCIEntity_.project), true));

        List<RCIEntity> resultList = em.createQuery(q).getResultList();

        RCIEntity get = resultList.get(0);

        **long count = get.getChildren().stream().count(); // output 0. Doesn't work**

        System.out.println("First count"+count);
        List<RCIEntity> subList = get.getChildren().subList(0, get.getChildren().size());
        **long count1 = subList.stream().count(); // works fine output 4.**

         System.out.println("2nd count "+count1);

**OUTPUT: First count0, 2nd count 4 **

Answer 1

所以最终这是 EclipseLink 2.5.2 版本的一个错误。并在 2.6.0 中修复