Hibernate: A Developer's Notebook

2.1. Writing a Mapping Document

Hibernate uses an XML document to track the mapping between Java classes and relational database tables. This mapping document is designed to be readable and hand-editable. You can also start by using graphical CASE tools (like Together, Rose, or Poseidon) to build UML dia grams representing your data model, and feed these into AndroMDA (http://www.andromda.org/), turning them into Hibernate mappings.

Don't forget that Hibernate and its extensions let you work in other ways, starting with classes or data if you've got them.

We'll write one by hand, showing it's quite practical.

We're going to start by writing a mapping document for tracks, pieces of music that can be listened to individually or as part of an album or play list. To begin with, we'll keep track of the track's title, the path to the file containing the actual music, its playing time, the date on which it was added to the database, and the volume at which it should be played (in case the default volume isn't appropriate because it was recorded at a very different level than other music in the database).

2.1.1. Why do I care?

You might not have any need for a new system to keep track of your music, but the concepts and process involved in setting up this mapping will translate to the projects you actually want to tackle.

2.1.2. How do I do that?

Fire up your favorite text editor, and create the file Track.hbm.xml in the src/com/oreilly/hh directory you set up in the previous chapter. (If you ...