The Java EE 6 Tutorial, Volume I

Automatic Table Generation in the roster Application

At deployment time the Enterprise Server will automatically drop and create the database tables used by roster. This is done by setting the toplink.ddl-generation property to drop-and-create-tables in persistence.xml.

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns=""
    <persistence-unit name="em" transaction-type="JTA">
            <property name="toplink.ddl-generation"

This feature is specific to the Java Persistence API provider used by the Enterprise Server, and is non-portable across Java EE servers. Automatic table creation is useful for development purposes, however, and the toplink.ddl-generation property may be removed from persistence.xml when preparing the application for production use, or when deploying to other Java EE servers.