Hibernate：使用增量和 Oracle Schema 的 ID 生成器
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Hibernate: ID generator using increment and Oracle Schema
提问by Krishna
I am using Hiberbnate 3.1.3. I have a mapping as below and when I try to insert a record into the TEST_TABLE, I get an Exception: 'Exception in thread "main" org.hibernate.exception.SQLGrammarException: could not fetch initial value for increment generator'
我正在使用 Hiberbnate 3.1.3。我有如下映射，当我尝试将记录插入到 TEST_TABLE 中时，出现异常：'线程“main”org.hibernate.exception.SQLGrammarException 中的异常：无法获取增量生成器的初始值'
<class name="com.test.app.to.TestTable" table="TEST_TABLE" schema="TEST">
<id name="testId" type="long">
<column name="TEST_ID" precision="12" scale="0" />
<generator class="increment"></generator>
</id>
</class>
I have default schema set as below in the cfg.xml as I need to use tables from the OTHER_SCHEMA as well in my application.
我在 cfg.xml 中设置了如下默认架构，因为我需要在我的应用程序中使用 OTHER_SCHEMA 中的表。
<property name="hibernate.default_schema">OTHER_SCHEMA</property>
In the above case it seems to be a Hibernate Bug as a read using a TestTable object works fine and uses the 'TEST' schema correctly, but the '<generator class="increment"></generator>'does not use the 'TEST' schema but uses the default 'OTHER_SCHEMA' for getting the max ID. The query generated for max ID reads as below:
在上述情况下，它似乎是一个休眠错误，因为使用 TestTable 对象读取工作正常并正确使用“TEST”模式，但'<generator class="increment"></generator>'不使用“TEST”模式而是使用默认“OTHER_SCHEMA”来获取最大值ID。为最大 ID 生成的查询如下所示：
Hibernate: select max(TEST_ID) from OTHER_SCHEMA.TEST_TABLE
I am not able to specify a schema for the generator and it is not using the schema="TEST" attribute of the class which I would expect it to use.
我无法为生成器指定架构，并且它没有使用我希望它使用的类的 schema="TEST" 属性。
How can this issue be resolved?
如何解决这个问题？
回答by ChssPly76
You canspecify schema for your generator using schemaparameter:
您可以使用schema参数为生成器指定架构：
<generator class="increment">
<param name="schema">TEST</param>
</generator>
Sadly, this is not well described in Hibernate documentation; you'd have to look at the API javadocin order to find that out.
遗憾的是，这在 Hibernate 文档中没有很好地描述；您必须查看API javadoc才能找到答案。
That said, Mark is right with regards to "increment" not being very efficient - it's also not safe in a cluster environment.
也就是说，马克关于“增量”效率不高的观点是正确的——它在集群环境中也不安全。
回答by user151019
If the hibernate default schema is OTHER_SCHEMA then if you do not supply a schema for a table then it will automatically add the default
如果休眠默认架构是 OTHER_SCHEMA 则如果您不为表提供架构，那么它将自动添加默认架构
Solution is you have to add a schema for all table names except one the default. In this case you might be better off if you set the hibernate default to your schema.
解决方案是您必须为所有表名添加一个模式，默认除外。在这种情况下，如果您将休眠默认设置为您的架构，您可能会更好。
Looking at the sequence using max(id) like that is not usually efficient, especially in Oracle which has sequences exactly for this use.
像这样查看使用 max(id) 的序列通常效率不高，尤其是在 Oracle 中，它的序列正好用于此用途。
