JPA GenerationType.AUTO不考虑带自动增量的列 [英] JPA GenerationType.AUTO not considering column with auto increment

问题描述

实体的ID使用 @Id注释。 和 @GeneratedValue

  @Id 
 @GeneratedValue（strategy = GenerationType.AUTO）
 @Column（name =id，length = 4，precision = 10，nullable = false）
 private Integer id; 
 

在SQL Server中，列正确设置为Identity with Seed 和增量等于1。

当我尝试持久化这个实体的实例时，Hibernate尝试查询hibernate_sequence表以获取ID值。由于我没有在我的模式中创建该表，我得到一个错误：

无法读取hi值：com.microsoft。 sqlserver.jdbc.SQLServerException：无效的对象名称'MySchema.hibernate_sequence'

如果我将生成类型更改为IDENTITY， p>

  @Id 
 @GeneratedValue（strategy = GenerationType.IDENTITY）
 @Column（name =id length = 4，precision = 10，nullable = false）
 private Integer id; 
 

我不能这样改变，因为我的应用程序将在MS SQL和ORACLE上运行，后者不支持自动递增的列。

据我所知，AUTO类型应该使用自动增量行为，如果底层数据库支持它，知道为什么不工作。

更新：

这花了我一些时间，

我正在使用具有以下行为的旧数据库：

• MSSQL：ID生成使用表IDENTITY


• ORACLE：ID生成使用触发器。触发器查询和更新存储所有下一个ids的自定义表。此表称为SEQ。

以下是使用一些id生成策略的结果：

• AUTO：在MSSQL中无效，如上所述


• IDENTITY：在MSSQL中有效，但不受Oracle支持


• native：在MSSQL中工作，但在ORACLE中失败。它失败，因为Hibernate激活它的默认序列策略，它使用hibernate_sequences.nextval。由于这是遗留应用程序，所以来自SEQ表（上面提到的）和hibernate_sequence 的值不同步（该特定表的SEQ's值在6120，hibernate_sequences'为1，这是预期的因为它直到现在还没有使用。）

所以我需要找出一种方法来配置该实体： p>

• 使用MSSQL身份特征
  OR


• 使用Oracle时，不要自动设置任何值




这可能会导致我在Oracle上的严重问题，当我需要插入依赖于主实体的实体（通过外键），因为Hibernate不知道哪个ID值是由外部触发器生成的。

解决方案

我有一个类似的问题，发现这个信息（更深入解释此处）。





将此属性添加到我的persistence.xml文件中修复了问题：

  property name =hibernate.id.new_generator_mappingsvalue =false/> 
  




I have a table with a simple int id column with Identity auto increment in SQL Server.

The entity's Id is annotated with @Id and @GeneratedValue

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "id", length = 4, precision = 10, nullable = false)
private Integer id;

In SQL Server the column is properly set as Identity with Seed and Increment equals to 1.

When I try to persist an instance of this entity, Hibernate tries to query the hibernate_sequence table to obtain the ID value. Since I haven't created that table in my schema I'm getting an error:

could not read a hi value: com.microsoft.sqlserver.jdbc.SQLServerException: Invalid object name 'MySchema.hibernate_sequence'

If I change the generation type to IDENTITY everything works as expected

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id", length = 4, precision = 10, nullable = false)
private Integer id;

I cannot change it this way, since my App will run both on MS SQL and ORACLE, and the latter does not support auto incremented columns.

As far as I know the AUTO type should use the auto increment behaviour if the underlying database has support to it, so I don't know why is not working.

UPDATE:

It took me some time but I was able to understand exactly what is going on.

I am working with legacy databases with the following behaviours:

• MSSQL: id generation uses table IDENTITY
• ORACLE: id generation uses a trigger. The trigger queries and updates a custom table where all the "next ids" are stored. This table is called SEQ.

Here is the outcome of using some id generation strategies:

• AUTO: does not work in MSSQL, as explained above
• IDENTITY: works in MSSQL but is not supported by Oracle
• "native": works in MSSQL but fails in ORACLE. It fails because Hibernate activates its default sequence strategy, which uses hibernate_sequences.nextval. Since this is a legacy application the values from the SEQ table (mentioned above) and the hibernate_sequences are not synchronized (SEQ's value for that particular table is at 6120, and hibernate_sequences' is at 1, which is expected since it was not used until now).

So what I need to figure out is a way to configure that entity to:

• Use MSSQL Identity feature OR
• When using Oracle, do not automatically set any value to the ID variable and leave everything up to the pre-existing trigger

This can cause me serious issues on Oracle when I need to insert entities that depend on the main entity (via foreign key), because Hibernate won't know which ID value was generated by the "external" trigger.

解决方案

I had a similar problem and found this information (deeper explained in here).

Adding this property into my persistence.xml file fixed the issue:

<property name="hibernate.id.new_generator_mappings" value="false" />

这篇关于JPA GenerationType.AUTO不考虑带自动增量的列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！