Java Persistent Objects (JPOX) relies on the use of Meta-Data for the classes to be persisted. The Meta-Data file(s) define how a class is persisted, from the basic information like which fields are persisted, down to whether the user wants to specify what column names are used in the database etc.

Generating JDO Meta-Data files can be time consuming and laborious if done by hand. Meta-Data file creation is an ideal candidate for automation to increase developer productivity and reduce human error. That, among other things, is what Javelin can provide.

From the Javelin website: "Javelin is a lightweight, visual, intuitive, non invasive, modeling and coding productivity tool. It automatically and silently facilitates the creation and management of the Java source files that implement the classes and relationships assembled in its class diagram editor. Javelin, because of its intimate knowledge of the software models designed within it, is also capable of automatically generating Meta-Data for a variety of persistence technologies, including JPOX/JDO2."

Javelin is well matched to newer software projects that do not yet have an established database schema design and where the object model will "drive" the form of the database schema. Luckily these tend to be the interesting projects. In contrast, retrofitting an object model to an existing schema is more likely to be a frustrating, more mechanical and less artistic persuit because the level of freedom and expressiveness realized in your object model may be constrained by the existing schema. If required Javelin will allow you to persist to an existing schema via the use of "Persistence directives" customizations in various components of the design that allow the developer to, for example, specify column names instead of using the default field name assignments.

Javelin will, by default, create and manage Java source files for any new classes that you create in its class diagram editor but it also has an import facility to allow you to import an existing set of Java source files in an existing project and start taking advantage of the productivity benefits of Javelin on that project.

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After you turn on the JPOX persistence support Javelin creates and maintains a set of JPOX Meta-Data files that specify how your object model is to be persisted. Whenever you add class, edit an attribute, change a name, create or edit a relationship etc. Javelin creates or updates the relevent mapping files, silently and automatically, to reflect those model changes in JPOX 1.1 specific Meta-Data files (.jdo).

To turn on JPOX support in a Javelin project:

1. With the project open select Options > Persistence and the Persistence Options dialog box will appear.

2. Click the radio button next to Java Data Objects (JDO) Specification.

3. In the drop down list box of JDO implementations choose JPOX 1.1 (JDO2)

In this same dialog box are options to configure:

Default Inheritance Mapping Strategy: flat, vertical or horizontal. This setting applies to all classes that do not override the default strategy. You can do comparitive performance analysis of various inheritance strategies quickly and easily by changing the strategy and regenerating all mapping files by selecting "Synchronization > Force resynchronization of all classes". Recreate your schema and run your application - nothing else needs to be done to change inheritance strategies.

In the "Class details" dialog box of any individual class you can override the default strategy.

Usage of a Join table for 1-N relationships

Usage of 2 Join tables for M-N relationships

Javelin is a Windows application but obviously because it deals with Java files your software projects can be deployed on any platform with a JVM. It may work with Wine on Linux but we await verification of this.

Download a 15 day trial of Javelin or read more about it at the Step Ahead Software web site.

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Disclaimer : JPOX does not provide support for nor endorse the use of Javelin. We simply provide visibility of its existence and potential benefits for your organisation. You can obtain support for Javelin from the Step Ahead Software web site.