log4p

After the news of IBM pulling back from the deal to buy Sun Microsystems rumors about other possible candidates scoured the web. Oracle was on top of most lists. Today the news hit the web. Oracle actually bought Sun (well, they’re still in the process of solving a lot legal stuff).

I don’t know why, but it makes me feel sad. Although I didn’t like everything Sun came up with they made and/or own a lot of stuff I like:

• Java/JVM
• MySQL
• Netbeans
• Glassfish
• JRuby/Jython
• Solaris (yes, I’ve cursed it as well)
• ZFS
• Project Looking Glass (Great in it’s time)

For sure they did some dreadful things as well:

• Java Desktop System
• JCreator
• The JSF spec
• java.util.Date
• Endless Sun Spot demo’s
• JavaFX

Still I sort of like them. Which Oracle never managed to achieve. Hopefully good will come from it… but I really think Oracle will gain far to much power on the Java side of the story to not cause agony in the community.What will happen to the JPA spec? What about JRuby? Time for a Fork?

One of the models a developed in a previous project used embedded/embeddable annotations to create a composite object. The (simplified) object model looks like this:

The embedded/embeddable solution would store the entire graph in a single table, all attributes flattened to one row:

That works great as long as you don't mind minor annoyances like:

• when loaded, embedded object are filled with null values if no attributes are present in the database.
• you have no constraints which need to be satisfied only if an entire object exists (ie. if I set videoattributes, the null value is required)

Or in other words: only do this if the objects are always supposed to be present. Which in the case above is simply not true. If you would like to describe audio-only content you don't want to set the 'required' video codec.

My current project is a spin-off of the project mentioned above and uses some concepts of the model on a new database. I decided to alter the mappings and give Audio- and VideoAttributes their own table. This proved to be somewhat harder then I expected:

• alter the embeddable annotation of Audio- and VideoAttributes, make them entities
• since Audio- and VideoAttributes are entities now the need an id
• add a reference to the AVAttributes object to Audio- and VideoAttributes
• create a bi-directional one-to-one mapping between avattributes and audio- and VideoAttributes. mappedBy on the Audio- and VideoAttributes side
• add cascade annotations to the Audio- and VideoAttributes in the AVAttributes class

I started out with generated id's for the Audio- and VideoAttributes. Hibernate will generate two columns in the AVAttributes containing a foreign keys to the Audio- and VideoAttributes tables. This synthetic id seemed a bit unnecessary IMHO. It took me a while to figure out how to do this. I ended up with the following annotations:

AVAttributes

AudioAttributes (Same annotations used for VideoAttributes)

The generated table structure looks like this:

Id's are automatically cascaded when a AVAttributes object is persisted. And yes, it's a lot of annotations and I even stripped out the JAXB2 annotations which are also present.