Hibernate使用PostgreSQL序列不会影响序列表 [英] Hibernate use of PostgreSQL sequence does not affect sequence table

问题描述

我已配置Hibernate使用PostgreSQL序列（通过注释）为主键 id 列生成值，如下所示：

<$ p $
@GeneratedValue（strategy = GenerationType.SEQUENCE，generator =pk_sequence）$ b @SequenceGenerator（name =pk_sequence，sequenceName =entity_id_seq）
@GeneratedValue $ b @Column（name =id，unique = true，nullable = false）
public int getId（）{
return this.id;
}

我在这个配置中看到的是，hibernate已经分配了 id 在持续时间上的值大于3000，而在使用的序列上的查询显示如下：

  database =＃select last_value from entity_id_seq; 
 last_value 
 ------------ 
 69 
  

（1 row）

问题：

是否有错误？ hibernate与序列表同步吗？

如果不是，它会在哪里存储最后生成的ID？

谢谢。

解决方案

我有同样的问题。它与Hibernate的id分配策略有关。当您选择 .EQUENCE 时，Hibernate使用HiLo策略，默认分配ID为50的块。因此，您可以像这样明确地设置 allocationSize 值：

  @Id 
 @SequenceGenerator name =pk_sequence，sequenceName =entity_id_seq，allocationSize = 1）
 @GeneratedValue（strategy = GenerationType.SEQUENCE，generator =pk_sequence）
 @Column（name =id，unique = true，nullable = false）
 public int getId（）{
 return this.id; 
} 
  

虽然我也听到了将HiLo策略与 allocationSize = 1 不是一个好习惯。有些人建议在需要处理数据库管理的序列时使用 GenerationType.AUTO

更新：我最终做了allocSize = 1，事情似乎按照我现在所期望的那样工作。我的应用程序是这样的，我不需要任何ID块，所以 YMMV 。 p>

I've configured Hibernate to use PostgreSQL sequence (via annotations) to generate values for primary key id column as follows:

@Id 
@SequenceGenerator(name="pk_sequence",sequenceName="entity_id_seq")
@GeneratedValue(strategy=GenerationType.SEQUENCE,generator="pk_sequence")
@Column(name="id", unique=true, nullable=false)
public int getId() {
    return this.id;
}

What I see with this configuration is that hibernate is already assigning id values > 3000 on persisting, whereas the query on used sequence shows the following:

database=# select last_value from entity_id_seq;
last_value 
------------
     69

(1 row)

Questions:
Is there anything wrong or not?
Should hibernate sync with the sequence table?
If not, where does it store the last generated id?

Thank you.

解决方案

I had the same problem. It is related to the id allocating strategies of Hibernate. Whe n you choose GenerationType.SEQUENCE, Hibernate uses HiLo strategy which allocates IDs in blocks of 50 by default. So you can explicitly set allocationSize value like this:

@Id 
@SequenceGenerator(name="pk_sequence",sequenceName="entity_id_seq", allocationSize=1)
@GeneratedValue(strategy=GenerationType.SEQUENCE,generator="pk_sequence")
@Column(name="id", unique=true, nullable=false)
public int getId() {
    return this.id;
}

Though, I've also heard opinions that using HiLo strategy with allocationSize=1 is not a good practice. Some people recommend to use GenerationType.AUTO instead when you have to deal with database-managed sequences

Update: I did end up going with allocationSize=1, and things seem to work as I expect now. My application is such that I don't really need blocks of IDs anyway, so YMMV.

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