Hibernate JPA序列（非Id） [英] Hibernate JPA Sequence (non-Id)

问题描述

是否可以为不是标识符/不是组合标识符的一部分的某个列使用DB序列？

我使用hibernate作为jpa提供程序，并且我有一个表有一些生成值的列（使用序列），尽管它们不是标识符。

我想要的是使用序列为实体创建新值，其中序列的列是 NOT （部分）主键：

  @Entity 
 @Table（name =MyTable）
 public class MyEntity {
 
 // ... 
 @Id // ... etc 
 public Long getId（）{
 return id; 
} 
 
 // note注意@Id here！但这不起作用... 
 @GeneratedValue（strategy = GenerationType.AUTO，generator =myGen）
 @SequenceGenerator（name =myGen，sequenceName =MY_SEQUENCE）
 @Column（name =SEQ_VAL，unique = false，nullable = false，insertable = true，updatable = true）
 public Long getMySequencedValue（）{
 return myVal; 
} 
 
} 
  

然后当我这样做时：

  em.persist（new MyEntity（））; 
  

将生成id，但是 mySequenceVal 属性也将由我的JPA提供程序生成。

为了清楚起见：我希望 Hibernate 生成 mySequencedValue 属性。我知道Hibernate可以处理数据库生成的值，但我不想使用触发器或除Hibernate之外的其他任何东西来为我的属性生成值。如果Hibernate可以为主键生成值，为什么它不能为一个简单的属性生成？

解决方案

寻找这个答案问题，我偶然发现了这个链接

看起来Hibernate / JPA不能为你的非id属性自动创建一个值。 @GeneratedValue 注释仅与 @Id 一起用于创建自动编号。

@GeneratedValue 注解只是告诉Hibernate数据库本身正在生成这个值。

该论坛建议的解决方案（或解决方法）是使用生成的ID创建一个单独的实体，如下所示：

 
 @Entity 
公共类GeneralSequenceNumber {
 @Id 
 @GeneratedValue（...）
私人长号码; 
} 
 
 @Entity 
 public class MyEntity {
 @Id .. 
 private Long id; 
 
 @OneToOne（...）
 private GeneralSequnceNumber myVal; 
} 
 

Is it possible to use a DB sequence for some column that is not the identifier/is not part of a composite identifier?

I'm using hibernate as jpa provider, and I have a table that has some columns that are generated values (using a sequence), although they are not part of the identifier.

What I want is to use a sequence to create a new value for an entity, where the column for the sequence is NOT (part of) the primary key:

@Entity
@Table(name = "MyTable")
public class MyEntity {

    //...
    @Id //... etc
    public Long getId() {
        return id;
    }

   //note NO @Id here! but this doesn't work...
    @GeneratedValue(strategy = GenerationType.AUTO, generator = "myGen")
    @SequenceGenerator(name = "myGen", sequenceName = "MY_SEQUENCE")
    @Column(name = "SEQ_VAL", unique = false, nullable = false, insertable = true, updatable = true)
    public Long getMySequencedValue(){
      return myVal;
    }

}

Then when I do this:

em.persist(new MyEntity());

the id will be generated, but the mySequenceVal property will be also generated by my JPA provider.

Just to make things clear: I want Hibernate to generate the value for the mySequencedValue property. I know Hibernate can handle database-generated values, but I don't want to use a trigger or any other thing other than Hibernate itself to generate the value for my property. If Hibernate can generate values for primary keys, why can't it generate for a simple property?

解决方案

Looking for answers to this problem, I stumbled upon this link

It seems that Hibernate/JPA isn't able to automatically create a value for your non-id-properties. The @GeneratedValue annotation is only used in conjunction with @Id to create auto-numbers.

The @GeneratedValue annotation just tells Hibernate that the database is generating this value itself.

The solution (or work-around) suggested in that forum is to create a separate entity with a generated Id, something like this:

@Entity
public class GeneralSequenceNumber {
  @Id
  @GeneratedValue(...)
  private Long number;
}

@Entity 
public class MyEntity {
  @Id ..
  private Long id;

  @OneToOne(...)
  private GeneralSequnceNumber myVal;
}

这篇关于Hibernate JPA序列（非Id）的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！