How to generate table from entities

I am currently working on a seam project using eclipse jpa tools; is it possible to 开发者_JAVA百科automatically generate sql tables from my entity definitions? If so, how do I achieve this?

It depends on the JPA implementation you are using. With Hibernate you can specify 'create' or 'update' in the hibernate.hbm2ddl.auto properties in persistence.xml:

<persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="2.0">
  <persistence-unit name="yourPersistenceUnit" transaction-type="JTA">
    <description>Your Persistence Unit</description>
    <jta-data-source>java:/DefaultDS</jta-data-source>
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <properties>
      <property name="hibernate.hbm2ddl.auto" value="create"/>
      <property name="hibernate.show_sql" value="true"/>
      <property name="hibernate.format_sql" value="true"/>
      <property name="hibernate.transaction.flush_before_completion" value="true"/>
      <property name="hibernate.dialect" value="org.hibernate.dialect.HSQLDialect"/>
    </properties>
  </persistence-unit>
</persistence>

Possible values for hibernate.hbm2ddl.auto property are:

• create: create database tables and indexes at startup
• create-drop: create database tables and indexes at startup and drop at shutdown
• update: when the application starts, check the database schema and update as needed adding missing tables and columns
• validate: when the application starts, check the database schema and fails if there is some missing table or column.