Enterprise Java Development@TOPIC@
In a previous chapter, you manually created a set of DDL files to create schema, delete rows from the schema in the database, and drop the schema from the database. Since your persistence provider knows how to work with schema, you can optionally get it to create schema for you rather than generating it manually. Even if you are working with legacy schema (and won't be changing the database), it is extremely helpful to see the persistence providers version of the schema to be able to more quickly determine a mis-match in the mapping rather than waiting until runtime testing. In order to add schema generation to your projects you can add one of the following; runtime schema generation or compile-time schema generation. Runtime schema generation is fine for examples and small prototypes, but compile-time generation is suitable for more realistic development scenarios.
runtime schema generation can be added to your project by adding the following property to your persistence-unit or hibernate.properties. Coldstart your database, comment out your SQL plugin, and re-run your tests if you want to verify the above will create the database at runtime.
#persistence.xml
<property name="hibernate.hbm2ddl.auto" value="create"/>
#hibernate.properties
hibernate.hbm2ddl.auto=create
compile-time schema generation can be added to your project with the following plugin entry. Add the following to your pluginManagement section. The following passive definition defines the reusable details for how we want to setup the hibernate plugin for generating database schema. It will write a drop script in a file called ...dropJPA.ddl and a create script called ...createJPA.ddl. It cannot create a delete script.
<build>
<pluginManagement>
<plugins>
...
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>hibernate3-maven-plugin</artifactId>
<version>${hibernate3-maven-plugin.version}</version>
<extensions>true</extensions>
<dependencies>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-entitymanager</artifactId>
<version>${hibernate3.version}</version>
</dependency>
</dependencies>
<executions>
<execution>
<id>generate-drop-ddl</id>
<phase>process-test-classes</phase>
<goals>
<goal>run</goal>
</goals>
<configuration>
<hibernatetool>
<hbm2ddl export="false" create="false" drop="true" format="true"
outputfilename="${project.artifactId}-dropJPA.ddl"/>
</hibernatetool>
</configuration>
</execution>
<execution>
<id>generate-create-ddl</id>
<phase>process-test-classes</phase>
<goals>
<goal>run</goal>
</goals>
<configuration>
<hibernatetool>
<hbm2ddl export="false" create="true" drop="false" format="true"
outputfilename="${project.artifactId}-createJPA.ddl"/>
</hibernatetool>
</configuration>
</execution>
</executions>
</plugin>
...
</plugins>
</pluginManagement>
</build>
Add the following active declaration to you pom to activate the plugin and fill in the module-specifics. Since this plugin can operate without a database server -- add it to the global build.plugins section and not within a profile.
<build>
...
<plugins>
<plugin>
<artifactId>hibernate3-maven-plugin</artifactId>
<groupId>org.codehaus.mojo</groupId>
<configuration>
<hibernatetool destdir="target/classes/ddl">
<classpath>
<path location="${project.build.directory}/classes" />
<path location="${project.build.directory}/test-classes" />
</classpath>
<jpaconfiguration persistenceunit="entityMgrEx"
propertyfile="${basedir}/target/test-classes/hibernate.properties" />
</hibernatetool>
</configuration>
</plugin>
<plugins>
Build your module and notice the generated JPA.ddl files
$ mvn clean process-test-classes
...
[hibernatetool] Executing Hibernate Tool with a JPA Configuration
[hibernatetool] 1. task: hbm2ddl (Generates database schema)
(...SLF4J warnings...)
[INFO] Executed tasks
[INFO]
[INFO] --- hibernate3-maven-plugin:3.0:run (generate-create-ddl) @ entityMgrEx ---
[INFO] Executing tasks
main:
[hibernatetool] Executing Hibernate Tool with a JPA Configuration
[hibernatetool] 1. task: hbm2ddl (Generates database schema)
...
---
---
`-- target
...
|-- classes
| |-- ddl
| | |-- emauto_create.ddl
| | |-- emauto_delete.ddl
| | |-- emauto_drop.ddl
| | |-- emauto_tuningadd.ddl
| | |-- emauto_tuningremove.ddl
| | |-- entityMgrEx-createJPA.ddl
| | `-- entityMgrEx-dropJPA.ddl
(Optionally) update your SQL plugin defintion added in previous chapter to reference the dynamically generated schema in the target tree.
If Eclipse reports an error for the plugin, add a lifecycle mapping for the hibernate3-maven-plugin to tell Eclipse to ignore the functionality of the plugin and eliminate any errors Eclipse might display. This goes with the definition you created for the sql-maven-plugin.
<pluginExecution>
<pluginExecutionFilter>
<groupId>org.codehaus.mojo</groupId>
<artifactId>hibernate3-maven-plugin</artifactId>
<versionRange>[2.2,)</versionRange>
<goals>
<goal>run</goal>
</goals>
</pluginExecutionFilter>
<action>
<ignore/>
</action>
</pluginExecution>
In this chapter you configured a Maven project to create a set of file artifacts as a part of the build that represent what the persistence provider believes the database should look like. You can optionally directly use this as a part of your module's database schema population, use it as a starting reference to manually create schema, or *most important* gain insight into what the persistence provider thinks your persistence unit is defined. This will save you some ignorant bliss that is usually followed by hours of debugging an incorrect mapping.