5.7. 辅助数据库对象(Auxiliary Database Objects)

Allows CREATE and DROP of arbitrary database objects, in conjunction with Hibernate's schema evolution tools, to provide the ability to fully define a user schema within the Hibernate mapping files. Although designed specifically for creating and dropping things like triggers or stored procedures, really any SQL command that can be run via a java.sql.Statement.execute() method is valid here (ALTERs, INSERTS, etc). There are essentially two modes for defining auxiliary database objects… 帮助CREATE和DROP任意数据库对象，与Hibernate的schema交互工具组合起来，可以提供在Hibernate映射文件中完全定义用户schema的能力。虽然这是为创建和销毁trigger(触发器）或stored procedure(存储过程）等特别设计的，实际上任何可以在java.sql.Statement.execute()方法中执行的SQL命令都可以在此使用（比如ALTER, INSERT，等等）。本质上有两种模式来定义辅助数据库对象…

第一种模式是在映射文件中显式声明CREATE和DROP命令：

<hibernate-mapping>
    ...
    <database-object>
        <create>CREATE TRIGGER my_trigger ...</create>
        <drop>DROP TRIGGER my_trigger</drop>
    </database-object>
</hibernate-mapping>

第二种模式是提供一个类，这个类知道如何组织CREATE和DROP命令。这个特别类必须实现org.hibernate.mapping.AuxiliaryDatabaseObject接口。

<hibernate-mapping>
    ...
    <database-object>
        <definition class="MyTriggerDefinition"/>
    </database-object>
</hibernate-mapping>

还有，这些数据库对象可以特别指定为仅在特定的方言中才使用。

<hibernate-mapping>
    ...
    <database-object>
        <definition class="MyTriggerDefinition"/>
        <dialect-scope name="org.hibernate.dialect.Oracle9Dialect"/>
        <dialect-scope name="org.hibernate.dialect.OracleDialect"/>
    </database-object>
</hibernate-mapping>