Hibernate: A Developer's Notebook

2. Introduction to Mapping

Now that we're in a position to work with Hibernate, it's worth pausing to reflect on why we wanted to in the first place, lest we remain lost in the details of installation and configuration. Object-oriented languages like Java provide a powerful and convenient abstraction for working with information at runtime in the form of objects that instantiate classes. These objects can link up with each other in a myriad of ways, and they can embody rules and behavior as well as the raw data they represent. But when the program ends, all the objects swiftly and silently vanish.

In this chapter:

• Writing a Mapping Document

• Generating Some Class

• Cooking Up a Schema

• Connecting Hibernate to MySQL

For information we need to keep around between runs, or share between different programs and systems, relational databases have proven to be hard to beat. They're scalable, reliable, efficient, and extremely flexible. So what we need is a means of taking information from a SQL database and turning it into Java objects, and vice versa.

There are many different ways of doing this, ranging from completely manual database design and coding, to highly automated tools. The general problem is known as Object/Relational Mapping, and Hibernate is a lightweight O/R mapping service for Java.

The "lightweight" designation means it is designed to be fairly simple to learn and use, and to place reasonable demands on system resources, compared to some of the other available tools. Despite this, ...