我怎样才能使用组合键内产生价值？ [英] How can I use generated value within composite keys?

问题描述

我有两个类documentlog和documentversion（与主键：INT DOC_ID和int docVersionID）与多到一的关系。我使用了一种名为CompundKey复合键类来管理的复合主键。我需要自动增量docver​​sionID，但我不能这样做。能否请你帮我在这方面？

  @Entity
@Table（NAME =Documentversion，模式=DocumentManagement）
公共类DocumentVersion实现Serializable { 私人CompoundKey ID;
 私人列表＆LT; D​​ocumentLog＆GT; documentLog; @OneToMany（的mappedBy =documentVersion，targetEntity = DocumentLog.class，
   级联= {CascadeType.PERSIST，CascadeType.MERGE，CascadeType.REFRESH}）
 公开名单＆LT; D​​ocumentLog＆GT; getDocumentLog（）{
  返回documentLog;
 }
 公共无效setDocumentLog（列表＆LT; D​​ocumentLog＆GT; documentLog）{
  this.documentLog = documentLog;
 } @EmbeddedId
 @AttributeOverride（NAME =DOC_ID，列= @列（名称=DOC_ID））
 公共CompoundKey的getId（）{
  返回ID;
 }
 公共无效SETID（CompoundKey ID）{
  this.id = ID;
 }
}
 

解决方案

该文档是关于该主题...

有点混乱

据我所知，组合键总是要的分配的应用程序（即非生成的）至少与标准JPA也是Hibernate的核心：

  

8.4.组件作为联合标识符

  
  

...

  
  

您不能使用一个IdentifierGenerator
  产生组合关键字。代替
  应用程序必须分配它自己
  标识符。

但事情可能会在不同的做法（见 HHH-2060 和/或位使用使用CompositeUserType有一个IdentifierGenerator一起替代这个线程）。

现在，最令人困惑的部分，从Hibernate注解3.5文档：

  

2.2.3.2.4。部分标识符生成

  
  

Hibernate支持自动
  代的部分标识符的
  属性。只需使用
   @GeneratedValue 上一个注释或
  几个ID属性。

  
  

...

  
  

您还可以生成一个 @EmbeddedId 类中的属性。

（和也请阅读反对使用此功能从Hibernate团队的警告）。

我没有任何与它的实际经验，但。

参考

• Hibernate的核心参考指南
  
  
  
  • 8.4.组件作为联合标识符
  
  


• Hibernate注解3.5参考指南
  
  
  
  • 2.2.3.2.4。部分标识符生成
  
  

I have two classes documentlog and documentversion(with primary keys: int doc_id and int docVersionID) with a many-to-one relationship. I used a composite key class called CompundKey to manage the compound primary key. I need to auto increment docversionID but I am not able to do that. Could you please help me in this regard?

@Entity
@Table(name = "Documentversion", schema = "DocumentManagement")
public class DocumentVersion implements Serializable { 

 private CompoundKey id;
 private List<DocumentLog> documentLog;

 @OneToMany(mappedBy="documentVersion", targetEntity=DocumentLog.class,  
   cascade ={CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REFRESH})
 public List<DocumentLog> getDocumentLog() {
  return documentLog;
 }
 public void setDocumentLog(List<DocumentLog> documentLog) {
  this.documentLog = documentLog;
 }

 @EmbeddedId 
 @AttributeOverride(name="doc_Id", column=@Column(name="doc_Id") )
 public CompoundKey getId() {
  return id;
 }
 public void setId(CompoundKey id) {
  this.id = id;
 } 
}

解决方案

The documentation is a bit confusing on this topic...

To my knowledge, composite keys always had to be assigned by the application (i.e. non generated) at least with standard JPA but also Hibernate Core:

8.4. Components as composite identifiers

...

You cannot use an IdentifierGenerator to generate composite keys. Instead the application must assign its own identifiers.

But things might be a bit different in practice (see HHH-2060 and/or this thread for an alternative using a CompositeUserType together with an IdentifierGenerator).

Now, the most confusing part, from the Hibernate Annotations 3.5 documentation:

2.2.3.2.4. Partial identifier generation

Hibernate supports the automatic generation of some of the identifier properties. Simply use the @GeneratedValue annotation on one or several id properties.

...

You can also generate properties inside an @EmbeddedId class.

(and please also read the warning from the Hibernate Team against using this feature).

I don't have any practical experience with it though.

References

• Hibernate Core Reference Guide
  • 8.4. Components as composite identifiers
• Hibernate Annotations 3.5 Reference Guide
  • 2.2.3.2.4. Partial identifier generation

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