Chapter 8. Legacy databases and custom SQL

Many examples presented in this chapter are about "difficult" mappings. The first time you'll likely have problems creating a mapping is with a legacy database schema that can't be modified. We discuss typical issues you encounter in such a scenario and how you can bend and twist your mapping metadata instead of changing your application or database schema.

We also show you how you can override the SQL Hibernate generates automatically. This includes SQL queries, DML (create, update, delete) operations, as well as Hibernate's automatic DDL-generation feature. You'll see how to map stored procedures and user-defined SQL functions, and how to apply the right integrity rules in your database schema. This section will be especially useful if your DBA needs full control (or if you're a DBA and want to optimize Hibernate at the SQL level).

As you can see, the topics in this chapter are diverse; you don't have to read them all at once. You can consider a large part of this chapter to be reference material and come back when you face a particular issue.