创建一个自定义的Hibernate UserType - isMutable（）是什么意思？ [英] Creating a custom Hibernate UserType - What does isMutable() mean?

问题描述

我在Hibernate中为一个项目创建一个自定义的UserType。直到我接触到isMutable方法时，它一直比较简单。我试图找出这种方法意味着什么，合同明智。

它是否意味着我创建UserType的类是不可变的，还是它意味着持有对此类实例的引用永远不会指向不同的对象实例？

我在 Hibernate社区发现了一些例子Wiki ，他们在那里返回true，因为对象本身是可变的 - http：//www.hibernate。组织/ 73.html 。

社区wiki中的其他示例在没有解决原因的情况下返回false，即使它们也是可变的。

I已经检查了JavaDoc，但它也不是很清楚。

从JavaDoc for

  public boolean isMutable（）
这种类型的对象是否可变？ 
返回：
 boolean 
  

从JavaDoc for 类型：

  public boolean isMutable（）
这种类型的对象是可变的。 （关于引用
对象...实体和集合被认为是不可变的，因为
他们管理自己的内部状态。）
返回：
布尔
  Hibernate会将标记为可变的类型视为可以改变（即需要一个UPDATE）没有指向一个新的引用。如果你为一个Hibernate加载的属性赋值一个新的引用，即使类型是不可变的，Hibernate也会识别这个 - 这种情况会一直发生，比如String字段。 
但是，如果你有一个StringBuilder字段，并且将它标记为不可变，那么如果修改StringBuilder，Hibernate将不是注意。
 
 
 
请参阅此博客文章以获取更多详情和示例项目。
 
I am creating a custom UserType in Hibernate for a project. It has been relatively straightforward until I came to the isMutable method. I am trying to figure out what this method means, contract-wise. 

Does it mean the class I am creating the UserType for is immutable or does it mean the object that holds a reference to an instance of this class will never point to a different instance?

I found some examples in the Hibernate Community Wiki where they returned true, because the object itself was mutable - http://www.hibernate.org/73.html. 

Other examples in the community wiki returned false without addressing why, even though they were also mutable.

I have checked the JavaDoc, but it's not very clear either.

From the JavaDoc for UserType:
public boolean isMutable()
    Are objects of this type mutable?
    Returns:
        boolean
From JavaDoc for Type:
public boolean isMutable()
    Are objects of this type mutable. (With respect to the referencing
    object ... entities and collections are considered immutable because
    they manage their own internal state.)
    Returns:
        boolean

解决方案
Hibernate will treat types marked as "mutable" as though they could change (i.e. require an UPDATE) without pointing to a new reference. If you assign a new reference to a Hibernate-loaded property Hibernate will recognize this even if the type is immutable - this happens all the time with, for instance, String fields.
But if, say, you have a StringBuilder field and you mark it as immutable Hibernate will not notice if you modify the StringBuilder.

See this blog post for more details and a sample project.

                        
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