休眠不能同时获取多个包 [英] Hibernate cannot simultaneously fetch multiple bags

问题描述

Hibernate在创建SessionFactory时抛出这个异常：

org.hibernate.loader.MultipleBagFetchException：不能同时获取多个包

这是我的测试用例：

Parent.java

  @Entity 
公共父母{
 
 @Id 
 @GeneratedValue（ strategy = GenerationType.IDENTITY）
 private Long id; 
 
 @OneToMany（mappedBy =parent，fetch = FetchType.EAGER）
 // @IndexColumn（name =INDEX_COL）如果我有这个问题解决，但我检索更多的孩子比我有，一个孩子是空的。 
私人列表< Child>儿童; 
 
 $ b  

Child.java

  @Entity 
 public Child {
 
 @Id 
 @GeneratedValue（strategy = GenerationType.IDENTITY）
私人长ID; 
 
 @ManyToOne 
私人父母; 
 
} 
  

这个问题怎么样？我能做什么？

---

编辑

好的，我遇到的问题是另一个父实体在我父母的内部，我真正的行为是这样的：
$ b

Parent.java

  @Entity 
公共父母{
 
 @Id 
 @GeneratedValue（strategy = GenerationType.IDENTITY）
 private长ID; 
 
 @ManyToOne 
私人AntoherParent anotherParent; 
 
 @OneToMany（mappedBy =parent，fetch = FetchType.EAGER）
 private List< Child>儿童; 
 
 $ b $ / code> 

AnotherParent.java

  @Entity 
 public AntoherParent {
 
 @Id 
 @GeneratedValue（strategy = GenerationType.IDENTITY）
私人长ID; 
 
 @OneToMany（mappedBy =parent，fetch = FetchType.EAGER）
 private List< AnotherChild> anotherChildren; 
 
} 
  

Hibernate不喜欢两个集合 FetchType.EAGER ，但这似乎是一个错误，我没有做不寻常的事情......

删除 FetchType.EAGER 来自父或 AnotherParent 解决了这个问题，但我需要所以真正的解决方案是使用 @LazyCollection（LazyCollectionOption.FALSE）而不是 FetchType （感谢 Bozho ）。

我认为更新版本的hibernate（支持JPA 2.0）应该能够处理这个问题。但除此之外，您可以通过注释收集字段来处理它：

  @LazyCollection（LazyCollectionOption.FALSE）
  

记得从 fetchType 属性> @ * ToMany 注解。

但是请注意，在大多数情况下a Set< Child> 比 List< Child> 更合适，所以除非你真的需要 List - 为 Set

Hibernate throws this exception during SessionFactory creation:

org.hibernate.loader.MultipleBagFetchException: cannot simultaneously fetch multiple bags

This is my test case:

Parent.java

@Entity
public Parent {

 @Id
 @GeneratedValue(strategy=GenerationType.IDENTITY)
 private Long id;

 @OneToMany(mappedBy="parent", fetch=FetchType.EAGER)
 // @IndexColumn(name="INDEX_COL") if I had this the problem solve but I retrieve more children than I have, one child is null.
 private List<Child> children;

}

Child.java

@Entity
public Child {

 @Id
 @GeneratedValue(strategy=GenerationType.IDENTITY)
 private Long id;

 @ManyToOne
 private Parent parent;

}

How about this problem? What can I do?

---

EDIT

OK, the problem I have is that another "parent" entity is inside my parent, my real behavior is this:

Parent.java

@Entity
public Parent {

 @Id
 @GeneratedValue(strategy=GenerationType.IDENTITY)
 private Long id;

 @ManyToOne
 private AntoherParent anotherParent;

 @OneToMany(mappedBy="parent", fetch=FetchType.EAGER)
 private List<Child> children;

}

AnotherParent.java

@Entity
public AntoherParent {

 @Id
 @GeneratedValue(strategy=GenerationType.IDENTITY)
 private Long id;

 @OneToMany(mappedBy="parent", fetch=FetchType.EAGER)
 private List<AnotherChild> anotherChildren;

}

Hibernate doesn't like two collections with FetchType.EAGER, but this seems to be a bug, I'm not doing unusual things...

Removing FetchType.EAGER from Parent or AnotherParent solves the problem, but I need it, so real solution is to use @LazyCollection(LazyCollectionOption.FALSE) instead of FetchType (thanks to Bozho for the solution).

解决方案

I think a newer version of hibernate (supporting JPA 2.0) should handle this. But otherwise you can work it around by annotating the collection fields with:

@LazyCollection(LazyCollectionOption.FALSE)

Remember to remove the fetchType attribute from the @*ToMany annotation.

But note that in most cases a Set<Child> is more appropriate than List<Child>, so unless you really need a List - go for Set

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