We saw in the JPA Tutorial the overall process for adding persistence
to a simple application. In that tutorial we persisted the objects to an RDBMS. Here we show the
differences when persisting instead to the db4o
Step 1 : Design your domain/model classes as you would do normally
Step 2 : Define their persistence definition using Meta-Data.
Step 3 : Compile your classes, and instrument them (using the DataNucleus enhancer).
Step 4 : Generate the database tables where your classes are to be persisted.
Step 5 : Write your code to persist your objects within the DAO layer.
Step 6 : Run your application.
The tutorial guides you through this. You can obtain the code referenced in this tutorial from
SourceForge (one of the files entitled "datanucleus-samples-tutorial-*").
The model classes are exactly the same here, so please refer to the
JPA Tutorial for details.
When defining the persistence of the classes, the only difference would be that we
omit the orm.xml file
since we aren't doing object-relational mapping with db4o.
In the JPA Tutorial we saw that we need to bytecode enhance
our classes to be persisted. This step is identical when using db4o so please refer to the
original tutorial for details.
With db4o we have no such concept as a "schema" and so this step is omitted.
We saw in the JPA Tutorial how to persist our objects
using JPA API calls. This is the same when using db4o so please refer to the original tutorial
Please note that DataNucleus doesn't currently support use of JPQL/SQL with
operations for querying will throw an Exception informing you of this.
We saw in the JPA Tutorial how to run our JPA-enabled
application. This is very similar when persisting to db4o. The only differences are
Put your db4o.jar in the CLASSPATH instead of the JDBC driver
JAR in the CLASSPATH instead of
to include the details for your DB4O datastore
file could be changed to be like this
<?xml version="1.0" encoding="UTF-8" ?>
<!-- Tutorial "unit" -->
<property name="datanucleus.ConnectionURL" value="db4o:file:db4o.db"/>
As you can see changing between an RDBMS and db4o is trivial. You don't need to change
your actual classes, or persistence code at all. It's simply a change to your runtime
If you have any questions about this tutorial and how to develop applications for use with
please read the online documentation since answers are to be found there.
If you don't find what you're looking for go to our
The DataNucleus Team