Generating the DDL(Create and DROP) Statements of JPA Entities in EclipseLink

This blog is about generating the DDL Statements (CREATE and DROP DDL)  for the entities managed by the JPA. The JPA implementation used here is EclipseLink.

I have used the following Person class to be managed as Entity.

package com.entities;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Person {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    int id;
    String fName;
    String lName;
    int age;

   //the setter, getter, methods for each of the attributes, toString,   

   //hashCode,  equals and default constructor are not shown here.
}

The persistence.xml file is as follows.

<?xml version="1.0" encoding="UTF-8"?>
<persistence:persistence version="1.0"
	xmlns:persistence="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/persistence ../../persistence_1_0.xsd ">
<persistence:persistence-unit name="simplePersistenceUnit">
<persistence:provider>org.eclipse.persistence.jpa.PersistenceProvider</persistence:provider>
<persistence:class>com.entities.Person</persistence:class>
<persistence:properties>
<persistence:property name="eclipselink.jdbc.driver" value="com.mysql.jdbc.Driver"/>
<persistence:property name="eclipselink.jdbc.url" value="jdbc:mysql://localhost:3306/default"/>
<persistence:property name="eclipselink.jdbc.user" value="root"/>
<persistence:property name="eclipselink.jdbc.password" value="developer"/>
	</persistence:properties>
	</persistence:persistence-unit>
</persistence:persistence>

The persistence.xml contains information about the database.

The DDL generation information is provided to the persistence manager via a java.util.Map object.

package com.test;

import java.util.HashMap;
import java.util.Map;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

import org.eclipse.persistence.config.PersistenceUnitProperties;

import org.junit.Before;
import org.junit.Test;

public class TestExampleJPA {

	EntityManager em;

	@Test
	public void testDDLGeneration() {
		Map<String, String> persistProperties = new HashMap<String, String>();
		persistProperties.put(PersistenceUnitProperties.DDL_GENERATION, "create-tables");
		persistProperties.put(PersistenceUnitProperties.DDL_GENERATION_MODE, "sql-script");
		persistProperties.put(PersistenceUnitProperties.APP_LOCATION, "C:\MyFolder\temp");
		EntityManagerFactory emf = Persistence.createEntityManagerFactory( "simplePersistenceUnit", persistProperties);
		em = emf.createEntityManager();
	}
}

I have specified the database information in the persistence.xml file and DDL generation information into a Map object and providing it at runtime when creating the EntityManagerFactory object. Both the information can be provided fully either as part of  persistence.xml or Map object. I have combined both approaches for providing configuration information to JPA.

On executing the above test case the following sql files which contains the DDL for CREATE and DROP are created in C:\MyFolder\temp folder.

References:

http://wiki.eclipse.org/EclipseLink/Examples/JPA/OutsideContainer

http://wiki.eclipse.org/Using_EclipseLink_JPA_Extensions_(ELUG)