jpa-schema-gen

jpa-schema-gen

Generates DDLs using the Hibernate with the provided dialect into a new sourceSet within the build directory. All that is necessary is a META-INF/persistence.xml with the proper configuration of dialect and set of entity classes.

Disclaimer: In contrast to virtually all other related plugins, this plugin does not intend to execute migrations. It is rather a developer tool to setup and manage migrations. The execution is left to tools that ship along with the application and, this way, establish a clear contract between setup and deployment. Example are the mechanisms of Spring Boot or the complementing CLI clients of https://github.com/rmee/boot.

Warning: Some frameworks like Spring Boot allow the setup of JPA without a META-INF/persistence.xml. This comes at the cost of not working outside Spring and, as a result, is so far also not supported by this plugin either. PRs welcomed. For now it should be minor inconvenience with the prospect of a many benefits to the development lifecycle.

Setup

Add this library to the classpath:

buildscript {
	dependencies {
	    ...
		classpath 'com.github.rmee:jpa-schema-gen:<VERSION>'
	}
}

Tasks

• generateSchema to generate the schema files. The output is written to build/generated/source/schema/.

Flyway Example

apply plugin: 'jpa-schema-gen'
jpaSchemaGen {
	packageName = 'com.example.demo'
	persistenceUnitName = 'DEMO-UNIT'
	configuration = 'runtime'
	target = 'FLYWAY'
	version = project.version
}

The output folder will host three different files following the Flyway naming conventions to setup tables, constraints and indices.

Liquibase Example

apply plugin: 'jpa-schema-gen'
jpaSchemaGen {
	packageName = 'com.example.demo'
	persistenceUnitName = 'DEMO-UNIT'
	configuration = 'runtime'
	target = 'LIQUIBASE'
	version = project.version
	liquibase{
		user = 'john' // USER and USERNAME from environment used as default
	 	fileName = 'liquibase-changelog.xml' 
	}
}

Additional Features

Filter Persistence Unit

To only generate a schema for a subset of Entity classes in a persistence unit, you can use the includeOnlyPackages property to list the packages (or package prefixes) of the classes that you want to include in the schema generation.

This is useful if your application has to include entities in its persistence unit that it does not manage directly. E.g., if you rely on a library that will create it's own tables but need to query these tables directly via JPA.

apply plugin: 'jpa-schema-gen'
jpaSchemaGen {
	packageName = 'com.example.demo'
	persistenceUnitName = 'DEMO-UNIT'
	configuration = 'runtime'
	target = 'FLYWAY'
	version = project.version
	includeOnlyPackages = ['com.example']
}

Limitations

The filtering of the persistence unit happens before the persistence provider gets its hands on the persistence unit. It only works if you explicitly list all Entity classes and declare <exclude-unlisted-classes>true</exclude-unlisted-classes>.

<persistence xmlns="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 http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
			 version="2.0">
	<persistence-unit name="DEMO-UNIT" transaction-type="RESOURCE_LOCAL">
		<class>com.example.demo.ExampleEntity</class>
		<class>org.excluded.ExcludedEntity</class>
		<exclude-unlisted-classes>true</exclude-unlisted-classes>
	</persistence-unit>
</persistence>

The mechanism used to implement the filtering is quite hack-y. The plugin only chooses that code path if includeOnlyPackages are configured. We recommend, not to configure that property if you don't need the filtering feature.