Chapter 10 - Making Your Objects Persistent—Object-Orientation and Databases

Summary

What We'll Learn in This Chapter

Why your persistence strategy is important for successful application development.

What terminology is commonly used with respect to persistence.

How to map objects to flat files.

How to map objects to relational databases, concentrating on several critical topics: the impedance mismatch; mapping objects to tables; implementing object relationships; inheritance mapping strategies; and mapping success factors.

How to use object-oriented databases and object/relational databases as your persistence mechanism.

Persistence deals with the issue of how one ensures that the objects that he or she works with last, or persist, between invocations of object-oriented applications. In other words, persistence addresses one's strategy for saving objects to permanent storage. There are four common mechanisms used to store objects: flat files, relational databases, object-oriented databases, and object/relational databases. Although you may have heard that mapping objects into a relational database is a nightmare, and it can be if you make a mistake, we'll see in this chapter that using relational databases to store your objects is a very viable approach to persistence.

The vast majority of business objects must be persistent, or in other words they need to be saved to permanent storage so that you can work with them in the future. Fortunately or unfortunately depending on your point of view, we have several mechanisms that we can use to make our objects persistent: flat files, relational databases, object-oriented databases, and object/relational databases. We will cover each of these mechanisms in detail, discussing the issues for how to use them to make your objects persistent.