Sun GlassFish Enterprise Server v3 Application Development Guide

Automatic Schema Generation

The automatic schema generation feature of the Enterprise Server defines database tables based on the fields or properties in entities and the relationships between the fields or properties. This insulates developers from many of the database related aspects of development, allowing them to focus on entity development. The resulting schema is usable as-is or can be given to a database administrator for tuning with respect to performance, security, and so on. This section covers the following topics:

Note –

Automatic schema generation is supported on an all-or-none basis: it expects that no tables exist in the database before it is executed. It is not intended to be used as a tool to generate extra tables or constraints.

Deployment won't fail if all tables are not created, and undeployment won't fail if not all tables are dropped. Instead, an error is written to the server log. This is done to allow you to investigate the problem and fix it manually. You should not rely on the partially created database schema to be correct for running the application.

Annotations

The following annotations are used in automatic schema generation: @AssociationOverride, @AssociationOverrides, @AttributeOverride, @AttributeOverrides, @Column, @DiscriminatorColumn, @DiscriminatorValue, @Embedded, @EmbeddedId, @GeneratedValue, @Id, @IdClass, @JoinColumn, @JoinColumns, @JoinTable, @Lob, @ManyToMany, @ManyToOne, @OneToMany, @OneToOne, @PrimaryKeyJoinColumn, @PrimaryKeyJoinColumns, @SecondaryTable, @SecondaryTables, @SequenceGenerator, @Table, @TableGenerator, @UniqueConstraint, and @Version. For information about these annotations, see the Java Persistence Specification.

For @Column annotations, the insertable and updatable elements are not used in automatic schema generation.

For @OneToMany and @ManyToOne annotations, no ForeignKeyConstraint is created in the resulting DDL files.

Generation Options

Schema generation properties or asadmin command line options can control automatic schema generation by the following:

Creating tables during deployment
Dropping tables during undeployment
Dropping and creating tables during redeployment
Generating the DDL files

Note –

Before using these options, make sure you have a properly configured database. See Specifying the Database.

Optional schema generation properties control the automatic creation of database tables. You can specify them in the persistence.xml file. For more information, see Using EclipseLink JPA Extensions for Schema Generation.

The following options of the asadmin deploy or asadmin deploydir command control the automatic creation of database tables at deployment.

Table 7–1 The asadmin deploy and asadmin deploydir Generation Options


Option	Default	Description
`--createtables`	none	If `true`, causes database tables to be created for entities that need them. If `false`, does not create tables. If not specified, the value of the `eclipselink.ddl-generation` property in `persistence.xml` is used.
`--dropandcreatetables`	none	If `true`, and if tables were automatically created when this application was last deployed, tables from the earlier deployment are dropped and fresh ones are created. If `true`, and if tables were not automatically created when this application was last deployed, no attempt is made to drop any tables. If tables with the same names as those that would have been automatically created are found, the deployment proceeds, but a warning is thrown to indicate that tables could not be created. If `false`, the `eclipselink.ddl-generation` property setting in `persistence.xml` is overridden.

The following options of the asadmin undeploy command control the automatic removal of database tables at undeployment.

Table 7–2 The asadmin undeploy Generation Options


Option	Default	Description
`--droptables`	none	If `true`, causes database tables that were automatically created when the entities were last deployed to be dropped when the entities are undeployed. If `false`, does not drop tables. If not specified, tables are dropped only if the `eclipselink.ddl-generation` property setting in `persistence.xml` is `drop-and-create-tables`.

For more information about the asadmin deploy, asadmin deploydir, and asadmin undeploy commands, see the Sun GlassFish Enterprise Server v3 Reference Manual.

When asadmin deployment options and persistence.xml options are both specified, the asadmin deployment options take precedence.

The Ant tasks sun-appserv-deploy and sun-appserv-undeploy are equivalent to asadmin deploy and asadmin undeploy, respectively. These Ant tasks also override the persistence.xml options. For details, see Chapter 3, Using Ant with Enterprise Server.