glassfish部署jpa问题

Question

我使用的是glassfish v3的默认数据库derby
  在glassfish的控制台里面能够ping的通
但是把jpa放到glassfish里面却并没有自动建表
下面是我jpa的persistence.xml的内容:
<persistence-unit name="trainPlanBookjpa">
        <jta-data-source>jdbc/__default</jta-data-source>
        <class>com.ouruan.otep.train.entity.TrainPlanBookEntity</class>
        <class>com.ouruan.otep.train.entity.WorkshopEntity</class>
        <properties>
            <property name="eclipselink.ddl-generation" value="drop-and-create-tables"/>
        </properties>
    </persistence-unit>
请教下大家，这是怎么回事??????