java - “Illegal attempt to map a non collection as a @OneToMany, @ManyToMany or @CollectionOfElements”

Question

早上好 Stackoverflow，

我的问题是它给了我错误:

Failed to create sessionFactory object.org.hibernate.AnnotationException: Illegal attempt to map a non collection as a @OneToMany, @ManyToMany or @CollectionOfElements: nl.scalda.pasimo.model.employeemanagement.EducationTeam.coachGroups

你知道为什么吗？

@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);
    }
}

Answer 1

异常很简单，说:非法尝试将非集合映射为@OneToMany、@ManyToMany 或@CollectionOfElements，所以原因在这里很明显，如果我们看看 Hibernate Collection mapping documentation它明确指出:

As a requirement persistent collection-valued fields must be declared as an interface type (see Example 7.2, “Collection mapping using @OneToMany and @JoinColumn”). The actual interface might be java.util.Set, java.util.Collection, java.util.List, java.util.Map, java.util.SortedSet, java.util.SortedMap...

您使用了 TreeSet，它是 Set<E> 和 SortedSet<E> 接口(interface)的实现类。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> :

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