JPA 级联持久性与实体 ElementCollection 键

我有两个像这样的 JPA 实体：

@Entity
class Foo {
    @Id
    private long id;
    // ...
}

@Entity
class Bar {
    @ElementCollection(targetClass = String.class, fetch = FetchType.LAZY)
    @MapKeyJoinColumn(name = "foo_id", referencedColumnName = "id")
    @MapKeyClass(Foo.class)
    @Column(name = "content")
    @CollectionTable(name = "bar_foo_content",
                     joinColumns = @JoinColumn(name = "bar_id", referencedColumnName = "id"))
    @ManyToMany(cascade = CascadeType.ALL)
    private Map<Foo, String> fooContent = Maps.newHashMap();
    // ...
}

如您所见，fooContent字段之间形成多对多关系Bar and Foo，所以我认为使用它是合适的@ManyToMany指定字段的级联。然而，当试图坚持Bar与几个Foo → String地图中的值，我得到以下异常：

javax.persistence.RollbackException: java.lang.IllegalStateException: During synchronization a new object was found through a relationship that was not marked cascade PERSIST: <<instance of Foo>>

显然，EclipseLink 不会级联我的持久性Foo实例。我该如何注释fooContent使级联持续工作？

你不需要@ManyToMany此处注释。操作于ElementCollections 总是级联的。