多线程休眠中的未知实体

Question

We are converting a large database from one DBMS to another. We are mostly using JDBC for this but there are some Hibernate calls mixed in. So far, a small portion of the database is taking seven hours to migrate. To mitigate this, we decided we could migrate different parts of the database simultaneously. We rewrote the migration routine to use threads. After wading through Java heap space issues and making sure we had separate JDBC and Hibernate sessions in each thread, we found ourselves with one last problem: We are getting Unknown entity: exceptions everywhere. We are creating a SchemaExport and executing it before any migration thread starts. What are we missing?

Answer 1

Apparently, Unknown entity is an exception which happens when hibernate doesn't know about the class which is referenced in the exception. eg, for the Myclass class:

Exception in thread "main" org.hibernate.MappingException: Unknown entity: data.Myclass

You need to have a <classname>.hbm.xml file, which corresponds to a hibernate mapping, in order for each class that must be known by hibernate, and also have these files referenced as resources in the main configuration file of hibernate. in hibernate.cfg.xml , this is the line to let hibernate know about the class Myclass :

<mapping resource="Myclass.hbm.xml" />