Java(TM) Boutique - Cultivating your relationship with Castor-JDO

Reviews : Cultivating your relationship with Castor-JDO :

Preface

Keld continues to shed light on Castor-JDO. This month we look at how Castor, an open-source project, helps to keep our Java object model consistent.

Looking Back

In my first article about Castor-JDO I showed you how to install Castor (and the MySQL database system), how to setup the xml- files that describe the database system that will be used, and the mappings between the fields in the database tables and the Java-properties in the beans. I also presented a couple of small programs that could insert data with relations into the database.

One observation we saw when we retrieved an object from the database was, that Castor automatically fetches all related objects. This is not always what we want since it might have a negative impact on performance. This time we'll take at look at what "lazy loading" can do for us.

The Test Case

Let me briefly introduce you to our test setup used in the first article.

Consider a collection of movies. Each is either in VHS or DVD format. For every movie we also register the actors. This gives us a small test case, but it still contains the common relations between entities: one-to-many and many-to-many:

There are two media types in the database: DVD and VHS. We also have two movies and three actors:

Movie title	Media	Actors
The Matrix	DVD	Keanu Reeves Laurence Fishburne
Chain Reaction	VHS	Keanu Reeves

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