Reviews : Java Books : Hibernate: A Developer's Notebook :

What about...

. . . Connecting to Oracle, or another favorite, shared, or legacy database that doesn't happen to be MySQL or HSQLDB? You've probably figured out that it's just as easy. All you need to do is change the hibernate.dialect setting in your hibernate.properties to reflect the kind of database you want to use. There are many dialects available, covering every free and commercial database I can think of. These built-in dialects are listed in Appendix C. If you need to work with a more obscure database, you may have to write your own dialect to support it, but that seems unlikely (and check to see if anyone's already started that effort).

Once you've chosen the dialect, you'll also need to set the hibernate.connection properties (driver, URL, username, and password — the other entries in Example 2-4 and Example 2-9) to the proper values for establishing a JDBC connection to your chosen database environment. If you're porting an existing project to use Hibernate, you'll be able to obtain these from the code or configuration of that project. And, naturally, you'll need to put the database's JDBC driver into your project's library directory.

Of course, if you're connecting to an existing or shared database, you won't be using Hibernate to create the schema. Instead, you'll write the mapping document to reflect the existing schema, either by hand or with the help of a tool like Middlegen (http://boss.bekk.no/ boss/middlegen), and then start working with the data in the form of persistent objects, as described in Chapter 3.

You can even use Hibernate to talk to multiple databases at the same time; you just need to create multiple SessionFactory instances with separate configurations. This goes beyond the simple, automatic configuration we demonstrate in Chapter 3, but there are examples in the Hibernate reference documentation. Of course, a persistent object can only be associated with a single session at a time, which means it can only be linked to a single database at once. With clever, careful coding, though, you can copy or move objects between different database systems, even with a different schema to represent them. That's way out of scope for this notebook, though!

Footnotes

[1] We're assuming you've already generated the code shown in Example 2-3, or there won't be any Java source to compile, and the schema generation will fail. The schema target doesn't invoke codegen to automatically generate code, in case you've manually extended any of your generated classes.

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