Chapter 8. Database and Data Patterns

Storage is the one constant in enterprise development. Enterprise systems are, essentially, information management systems. To the user, the value of these applications comes from the centralization of information resources, which allows broader access and more flexible interaction. Of course, you can maintain an entire information model in memory, but that's not the best method: if someone trips over the cord, your business is back to square one. So production applications implement persistence, storing information to reliable media.

This chapter focuses on patterns for implementing and optimizing persistent storage in the business tier. The first section introduces some basic patterns for accessing persistent resources: the Data Access Object (DAO) pattern and the Procedure Access Object (PAO) pattern.

The rest of the chapter focuses on solving recurring problems in database-backed applications. Since Java object graphs generally store relations between objects directly, we need to translate Java's direct object-to-object relationships into something that we can store in a database. The solution is a primary key: a unique identifier associated with each logical entity in the database, which can be used to represent the relationships between objects. Since unique primary keys are so important to the database side of an application, we discuss patterns for generating and managing them.

As the primary key issue implies, there's no single, standard way to translate the data in an object model to a set of database tables (or to get the data from the database back into objects). So we'll finish the chapter with a look at a few database-object modeling approaches.