“非法尝试将非集合映射为@ OneToMany，@ ManyToMany或@CollectionOfElements”

问题描述

早上好Stackoverflow，

Good morning Stackoverflow,

我遇到的问题是它给了我错误：

I have the problem that it gives me the error:

您知道为什么吗？

@OneToMany(cascade=CascadeType.ALL, targetEntity=CoachGroup.class)
@JoinColumn(name="id")
private TreeSet<CoachGroup> coachGroups = new TreeSet<>();
private SessionFactory factory;

private void initialiseFactory() {
    try {
        factory = new Configuration().configure().buildSessionFactory();
    } catch (Throwable ex) {
        System.err.println("Failed to create sessionFactory object." + ex);
        throw new ExceptionInInitializerError(ex);
    }
}

推荐答案

异常很简单，它说：试图将非集合映射为@ OneToMany，@ ManyToMany或@CollectionOfElements ，因此原因很明显，如果我们看一下明确指出：

The Exception is straightforward and says : Illegal attempt to map a non collection as a @OneToMany, @ManyToMany or @CollectionOfElements, so the cause is obvious here and if we take a look at the Hibernate Collection mapping documentation it clearly states that:

您使用了这是一个实现 Set< E> 和 SortedSet< E> 接口的 class 。因此，您的实际映射不适用于 TreeSet ，您应该使用 Set< CoachGroup> 而不是 TreeSet< CoachGroup> ：

And you used TreeSet which is an implementation class for both Set<E> and SortedSet<E> interfaces. So your actual mapping won't work with TreeSet, you should use a Set<CoachGroup> instead of a TreeSet<CoachGroup>:

private Set<CoachGroup> coachGroups = new HashSet<CoachGroup>();

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