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我在尝试从数据库中获取 Set<> Collection 时遇到问题。这是代码的相关部分：

@Entity

public Class User { 
    ... 

    @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    private Set<User> userFriends;
    @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    private Set<FriendRequest> friendRequests;
    @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    private Set<FriendRequest> sentRequests;
}

我试图将级联更改为 CascadeType.Persist 并且仍然遇到同样的问题。如果有人知道这个问题，我也很乐意了解我做错了什么以及 CascadeTypes 之间的区别（至少何时使用每个）。

这是我得到的 StackTrace：

Exception in thread "main" java.lang.StackOverflowError
    at java.util.HashMap$KeyIterator.<init>(Unknown Source)
    at java.util.HashMap$KeySet.iterator(Unknown Source)
    at java.util.HashSet.iterator(Unknown Source)
    at java.util.AbstractCollection.toString(Unknown Source)
    at org.hibernate.collection.internal.PersistentSet.toString(PersistentSet.java:328)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at MyRally1.demoRally.beans.User.toString(User.java:191)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at java.util.AbstractCollection.toString(Unknown Source)
    at org.hibernate.collection.internal.PersistentSet.toString(PersistentSet.java:328)

谢谢 ！

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