Glassfish and Automatic Table Generation (Java2db)

Pramod Gopinath's Weblog

Glassfish has a feature by which we could automatically create the database schema at the time of application deployment. This is also referred to as the “java2db” feature. Having this feature enables the developer to focus on creating the entity beans and let the application server define tables based on the fields in the entity beans and the relationship between them.

Currently we support java2db from within the application server environment. Very shortly we would be adding support for this feature in the out of container case.

How to enable the java2db feature for a ejb 3.0 ear ?

To enable java2db for an ejb 3.0 ear define the following properties for a persistence unit descriptor in the persistence.xml.

Property Name	Description
toplink.ddl-generation	Possible values of “create-tables"/"drop-and-create-tables"/"none". The default value is “none”.
toplink.create-ddl-jdbc-file-name	Name of the create jdbc ddl file
toplink.drop-ddl-jdbc-file-name	Name of the drop jdbc ddl file
toplink.application-location	In the context of the application server, this property is not to be defined by the user. In the code we set this property to be the app generated directory. This property would be used for the out of container case to define the location where one would want the jdbc ddl files to be stored.

e.g. of a persistence.xml usage could be

Example of a simple persistence.xml file:
<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence">
    <persistence-unit name ="em1">
        <jta-data-source>jdbc/DataSource1</jta-data-source>
        <properties>
          <property name="toplink.ddl-generation" value="drop-and-create-tables"/>
          <property name="toplink.create-ddl-jdbc-file-name" value="create_ora.jdbc"/>
          <property name="toplink.drop-ddl-jdbc-file-name" value="drop_ora.jdbc"/>
        </properties>
    </persistence-unit>
</persistence>

How to enable java2db feature w/o changing the ejb3.0 ear ?

The easiest way to enable this feature w/o changing the application ear is by using the asadmin cli commands :

• createtables=true/false. Specified at deploy time to ensure that the tables are created in the database.

• dropandcreatetables=true/false. Specified at redeploy time to ensure that the old tables are dropped and new ones created at redeploy time.

• droptables=true/false. Specified at undeploy time to ensure that the tables are dropped from the database.

These are the same commands that work with our application server for cmp2.x beans. These options overwrite the setting of the properties that might be defined in the persistence.xml.

example :

1. Command to deploy an ejb3.0 application that does not contain the properties defined but still create the required tables in the database :

   $GLASSFISH_HOME/bin/asadmin deploy --retrieve . --user admin --password adminadmin --host localhost --port 4848 --createtables=true --name onetomany --force=true /export/home/tools/ejb30_related/persistence-onetomanyApp.ear

2. Command to redeploy an ejb3.0 application that does not contain the properties and ensure that the tables get recreated in the database :

   $GLASSFISH_HOME/bin/asadmin deploy --retrieve . --user admin --password adminadmin --host localhost --port 4848 --dropandcreatetables=true --name onetomany --force=true /export/home/tools/ejb30_related/persistence-onetomanyApp.ear

3. Command to undeploy the ejb3.0 application that does not contain the properties and ensure that the tables get dropped from the database :

   $GLASSFISH_HOME/bin/asadmin undeploy --user admin --password adminadmin --host localhost --port 4848 --droptables=true onetomany

How does the admin cli commands interact/affect the properties if they are defined in persistence.xml ?

The cli options (--createtables/--dropandcreatetables/--droptables) take precedence over the properties in the persistence.xml.

Lets take an example to further explain this :

The user has defined the following in their persistence.xml -> toplink.ddl-generation : drop-and-create-tables

and then when deploying the application has specified -> --createtables=false.

In this case we would create the jdbc ddl statements but we will not execute the ddl statements against the database.

But if the cli option --createtables option is not defined at the deploy time, we would create the jdbc ddl statements and also execute the ddls against the database.

What happens if the jdbc ddl file names are not specified in the persistence.xml ?

This situation is similar to the cmp2.x case and we end up create ddl files with some default names. We try to create the name of the file by prepending the application and/or module name followed by the persistence unit name and then a static string of the form "createDDL.jdbc" or "dropDDL.jdbc".

So you might see files with names like

default_em_dropDDL.jdbc and default_em_createDDL.jdbc

OR

realApp_war1_ejb_em1_dropDDL.jdbc and realApp_war1_ejb_em1_createDDL.jdbc

(this is case where the persistence.xml is defined in a war file)

How to enable java2db for Derby database?

To enable java2db feature for the bundled Derby database ensure that the persistence unit section of your persistence.xml file has the following entries:

    <persistence-unit name =...>
        <!-- the datasource pointing to the bundled derby database -->
        <jta-data-source>jdbc/__default</jta-data-source>
        <properties>
          <!--Enable the java2db feature -->
          <property name="toplink.ddl-generation" value="drop-and-create-tables"/>
        </properties>
    </persistence-unit>
</persistence>

Do all the asadmin command options for java2db defined for Sun Application Server 8.x work as is with Glassfish ?

Not at this point of time. There are options like –uniquetablenames and –dbvendorname that can be defined for Sun Application Server 8.x and are currently not supported in Glassfish. If and when we introduce support for these features this document would be updated to reflect the same.

Which are the source files in Glassfish that deal with providing support for the various databases ?

Below is chart that provides information about the internal source files and the corresponding databases that they support in Glassfish.

Database Name	Platform
Oracle	oracle.toplink.essentials.platform.database.oracle.OraclePlatform
Cloudscape	oracle.toplink.essentials.platform.database.CloudscapePlatform
Derby	oracle.toplink.essentials.platform.database.DerbyPlatform
DB2	oracle.toplink.essentials.platform.database.DB2Platform
Sybase	oracle.toplink.essentials.platform.database.SybasePlatform
SqlServer	oracle.toplink.essentials.platform.database.SQLServerPlatform
Informix	oracle.toplink.essentials.platform.database.InformixPlatform
PointBase	oracle.toplink.essentials.platform.database.PointBasePlatform
Mysql	oracle.toplink.essentials.platform.database.MySQL4Platform
PostgreSQL	oracle.toplink.essentials.platform.database.PostgreSQLPlatform

Posted by pramodg ( Dec 07 2005, 12:11:06 PM PST ) Permalink Comments [12]