急切地获取后执行@PostLoad？

发布于 2024-10-08 18:26:45 字数 1609 浏览 4 评论 0原文

使用 JPA2/Hibernate，我创建了一个实体 A，它具有到实体 X 的单向映射（见下文）。在 A 内部，我还有一个瞬态成员“t”，我试图使用 @PostLoad 方法来计算它。计算需要访问关联的 X：

@Entity  
public class A {  
    // ...
    @Transient
    int t;

    @OneToMany(orphanRemoval = false, fetch = FetchType.EAGER)  
    private List listOfX;  

    @PostLoad
    public void calculateT() {
        t = 0;
        for (X x : listOfX)
            t = t + x.someMethod();
    }
}

但是，当我尝试加载此实体时，出现“org.hibernate.LazyInitializationException：非法访问加载集合”错误。

 at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:363)
 at org.hibernate.collection.AbstractPersistentCollection.read(AbstractPersistentCollection.java:108)
 at org.hibernate.collection.PersistentBag.get(PersistentBag.java:445)
 at java.util.Collections$UnmodifiableList.get(Collections.java:1154)
 at mypackage.A.calculateT(A.java:32)

在调试时查看hibernate的代码（AbstractPersistentCollection.java），我发现：

1）我的@PostLoad方法在“listOfX”成员初始化之前被调用
2) Hibernate 的代码有一个显式检查，以防止在 @PostLoad 期间初始化急切获取的集合：

 protected final void initialize(boolean writing) {
  if (!initialized) {
   if (initializing) {
    throw new LazyInitializationException("illegal access to loading collection");
   }
   throwLazyInitializationExceptionIfNotConnected();
   session.initializeCollection(this, writing);
  }
 }

我想解决此问题的唯一方法是停止使用 @PostLoad 并将初始化代码移动到 getT() 访问器中，添加一个同步块。但是，我想避免这种情况。

那么，有没有办法在调用 @PostLoad 之前执行急切获取？我不知道 JPA 设施可以做到这一点，所以我希望有一些我不知道的事情。

另外，也许 Hibernate 的专有 API 可以控制这种行为？

原文

Using JPA2/Hibernate, I've created an entity A that has a uni-directional mapping to an entity X (see below). Inside A, I also have a transient member "t" that I am trying to calculate using a @PostLoad method. The calculation requires access to the assosiated Xs:

@Entity  
public class A {  
    // ...
    @Transient
    int t;

    @OneToMany(orphanRemoval = false, fetch = FetchType.EAGER)  
    private List listOfX;  

    @PostLoad
    public void calculateT() {
        t = 0;
        for (X x : listOfX)
            t = t + x.someMethod();
    }
}

However, when I try to load this entity, I get a "org.hibernate.LazyInitializationException: illegal access to loading collection" error.

 at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:363)
 at org.hibernate.collection.AbstractPersistentCollection.read(AbstractPersistentCollection.java:108)
 at org.hibernate.collection.PersistentBag.get(PersistentBag.java:445)
 at java.util.Collections$UnmodifiableList.get(Collections.java:1154)
 at mypackage.A.calculateT(A.java:32)

Looking at hibernate's code (AbstractPersistentCollection.java) while debugging, I found that:

1) My @PostLoad method is called BEFORE the "listOfX" member is initialized
2) Hibernate's code has an explicit check to prevent initialization of an eagerly fetched collection during a @PostLoad:

 protected final void initialize(boolean writing) {
  if (!initialized) {
   if (initializing) {
    throw new LazyInitializationException("illegal access to loading collection");
   }
   throwLazyInitializationExceptionIfNotConnected();
   session.initializeCollection(this, writing);
  }
 }

The only way I'm thinking to fix this is to stop using @PostLoad and move the initialization code into the getT() accessor, adding a synchronized block. However, I want to avoid that.

So, is there a way to have eager fetching executed prior to @PostLoad being called? I don't know of a JPA facility to do that, so I'm hoping there's something I don't know.

Also, perhaps Hibernate's proprietary API has something to control this behaviour?

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相权↑美人 2024-10-15 18:26:45

这可能为时已晚，但 hibernate 似乎不支持默认的 jpa fetchtype 选项

@OneToMany(orphanRemoval = false, fetch = FetchType.EAGER)

您必须使用 hibernate 特定的选项：

@LazyCollection(LazyCollectionOption.FALSE)

This might be too late, but hibernate seems not to support the default jpa fetchtype option

@OneToMany(orphanRemoval = false, fetch = FetchType.EAGER)

You must use the hibernate specific one:

@LazyCollection(LazyCollectionOption.FALSE)

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柠栀 2024-10-15 18:26:45

我不知道如何解决这个问题，但我认为一点重构可能会有所帮助，想法是将代码移动到 @PostConstruct

所以例如你的类将是：

@Entity  
public class A {  
    // ...
    @Transient
    int t;

@OneToMany(orphanRemoval = false, fetch = FetchType.EAGER)  
private List listOfX;  

@PostConstruct
public void calculateT() {
    t = 0;
    for (X x : listOfX)
        t = t + x.someMethod();
}

}

服务器将调用一旦完成对 bean 的所有容器服务的初始化，就立即进行 PostConstruct。

I don't know how to fix this but I think a little refactoring might help, the idea would be to move the code to a @PostConstruct

so for example your class would be:

@Entity  
public class A {  
    // ...
    @Transient
    int t;

@OneToMany(orphanRemoval = false, fetch = FetchType.EAGER)  
private List listOfX;  

@PostConstruct
public void calculateT() {
    t = 0;
    for (X x : listOfX)
        t = t + x.someMethod();
}

}

The server will call PostConstruct as soon as it has completed initializing all the container services for the bean.

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