事物保存不了

ERROR - Exception occurred during processing request: ids for this class must be manually assigned before calling save(): cn.czq.entity.Product; nested exception is org.hibernate.id.IdentifierGenerationException: ids for this class must be manually assigned before calling save(): cn.czq.entity.Product

org.springframework.orm.hibernate3.HibernateSystemException: ids for this class must be manually assigned before calling save(): cn.czq.entity.Product; nested exception is org.hibernate.id.IdentifierGenerationException: ids for this class must be manually assigned before calling save(): cn.czq.entity.Product

at org.springframework.orm.hibernate3.SessionFactoryUtils.convertHibernateAccessException(SessionFactoryUtils.java:690)

一直这个问题好恼火啊