Changing Persistence Unit dynamically - JPA

Question

Persistence units in persistence.xml are created during building the application. As I want to change the database url at runtime, is there any way to modify the persistence unit at runtime? I supposed to use different database other than pre-binded one after distributed.

I'm using EclipseLink (JPA 2.1)

Answer 1

Keep the persistence unit file (Persistence.xml) as it's. You can override the properties in it as follows.

EntityManagerFactory managerFactory = null;
Map<String, String> persistenceMap = new HashMap<String, String>();

persistenceMap.put("javax.persistence.jdbc.url", "<url>");
persistenceMap.put("javax.persistence.jdbc.user", "<username>");
persistenceMap.put("javax.persistence.jdbc.password", "<password>");
persistenceMap.put("javax.persistence.jdbc.driver", "<driver>");

managerFactory = Persistence.createEntityManagerFactory("<current persistence unit>", persistenceMap);
manager = managerFactory.createEntityManager();

Answer 2

You can use Persistence.createEntityManagerFactory(Map) to pass properties to choose the database URL and other settings.

Answer 3

In Long-lived Session Architecture you should create a Plug-in-Framework.

Therefore you need to create a different Thread-Group and Class-Repository.

This might be your Class-Loader-Tree

• System-Class-Loader (usually a URLClassLoader, contains the Entitys)
  • JPA-Class-Loader
    • Load your jpa.jar with persistence.xml inside, specify the Database-Configuration from Application-Class-Loader
    • Instanciate your entityManager/session-factory.
    • Load any plugin you need to work with the DataBase. Execute Unit-Tests (;D) and Plugin-Integration-Tests.

Answer 4

If you are using Thorntail framework, you can wire-up the persistence.xml file to fetch runtime variables from "project-defaults.yml" file.

<persistence-unit name="java:jboss/datasources/my-postgres-ds">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <class>com.package.jpa.EntityClass1</class>
    <class>com.package.jpa.EntityClass2</class>
    <class>com.package.jpa.EntityClass3</class>
    <properties>
        <property name="hibernate.archive.autodetection" value="class"/>
        <property name="hibernate.show_sql" value="true"/>
        <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect"/>


        <property name="hibernate.connection.url"
                  value="${thorntail.datasources.data-sources.my-postgres-ds.connection-url}"/>
        <property name="hibernate.connection.username"
                  value="${thorntail.datasources.data-sources.my-postgres-ds.user-name}"/>
        <property name="hibernate.connection.password"
                  value="${thorntail.datasources.data-sources.my-postgres-ds.password}"/>


        <property name="hibernate.default_schema" value="public"/>
        <property name="hibernate.hbm2ddl.auto" value="update"/>
    </properties>

</persistence-unit>

Take note of the dynamic DB values in ${...} as the point to values in the project-default.yml file.

Then you project-defaults.yml file will have an entry like this:

    thorntail:
       http:
         port: 8989
       datasources:
          data-sources:
             my-postgres-ds:
                driver-name: my-postgres-driver
                connection-url: "jdbc:postgresql://localhost:5432/my-db-name"
                user-name: my-user-name
                password: "my-password#"
          jdbc-drivers:
             my-postgres-driver:
                driver-module-name: org.postgresql
                driver-xa-datasource-class-name: org.postgresql.xa.PGXADataSource

I expect this should also work for Spring boot using application.properties and persistence.xml