hibernate @ManyToMany 双向急切获取

发布于 2024-09-28 14:51:15 字数 378 浏览 5 评论 0原文

我有一个我认为应该很常见的问题，但我找不到答案。

我有 2 个对象：组和用户。我的类看起来像这样：

class Group
{
  @ManyToMany(fetch = FetchType.EAGER)
  List<User> users;
}

class User
{
  @ManyToMany(fetch = FetchType.EAGER)
  List<Group> groups;
}

现在，当我尝试从数据库中获取用户时，它会带来其所有组，所有组都会带来其所有用户，依此类推。最后，我得到了一个 stackoverflow 异常。

我怎样才能解决这个问题，同时仍然拥有双向关联并能够访问列表中的对象？

原文

I have a question which I think should be pretty common but I can't find an answer.

I have 2 objects: Group and User. My classes look something like this:

class Group
{
  @ManyToMany(fetch = FetchType.EAGER)
  List<User> users;
}

class User
{
  @ManyToMany(fetch = FetchType.EAGER)
  List<Group> groups;
}

Now, when I try to get a User from the database it brings all its groups and all groups bring all its users and so on. Finally, I'm getting a stackoverflow exception.

How can I solve this issue and still have my bidirectional association and the ability to reach the objects in the lists?

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灯角 2024-10-05 14:51:15

如果您使用 mappedBy 属性（您无论如何都应该使用）将双向关联的一侧作为关联的拥有一侧，您是否会遇到同样的问题？像这样：

@Entity public class Group {
  ...
  @ManyToMany(fetch = FetchType.EAGER, mappedBy="groups")
  List<User> users;
}

@Entity public class User {
  ...
  @ManyToMany(fetch = FetchType.EAGER)
  List<Group> groups;
}

更新： 我找不到任何证据表明禁止在双向关联的两侧使用 EAGER 获取，据我所知，没有提到这样的限制在 Hibernate 文档和/或 JPA 规范中。

实际上，根据 Emmanuel Bernard 对一个（某种程度上相似）问题的评论：

LAZY 或 EAGER 应该与代码库中的无限循环问题正交。 Hibernate 知道如何处理循环图

对我来说，上面的内容非常清楚，Hibernate 应该能够处理您的映射（正如我在评论中提到的），并且我很想将任何矛盾的行为视为错误。

如果您可以提供一个可以重现问题的测试用例，我的建议是提出一个问题。

Do you get the same problem if you make one of the sides of your bidirectional assocation the owning side of the association using the mappedBy attribute (that you should use anyway)? Like this:

@Entity public class Group {
  ...
  @ManyToMany(fetch = FetchType.EAGER, mappedBy="groups")
  List<User> users;
}

@Entity public class User {
  ...
  @ManyToMany(fetch = FetchType.EAGER)
  List<Group> groups;
}

Update: I can't find any evidence that using EAGER fetching on both sides of a bidirectional association is forbidden and AFAIK, there is no mention of such a restriction in the Hibernate documentation and / or the JPA specification.

Actually, according to this comment from Emmanuel Bernard to a (somehow similar) issue:

LAZY or EAGER should be orthogonal to an infinite loop issue in the codebase. Hibernate knows how to handle cyclic graphs

For me, the above is pretty clear, Hibernate should be able to handle your mapping (as I mentioned in a comment) and I would be tempted to consider any contradictory behavior as a bug.

If you can provide a test case allowing to reproduce the problem, my suggestion would be to open an issue.

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