Enterprise JavaBeans 3.1, 6th Edition

Chapter 10. Mapping Persistent Objects

In this chapter, we take a thorough look at the process of developing entity beans—specifically, mapping them to a relational database. A good rule of thumb is that entity beans model business concepts that can be expressed as nouns. Although this is a guideline rather than a requirement, it helps determine when a business concept is a candidate for implementation as an entity bean. In grammar school, you learned that nouns are words that describe a person, place, or thing. The concepts of “person” and “place” are fairly obvious: a person entity might represent a customer or passenger, and a place entity might represent a city or port of call. Similarly, entity beans often represent “things”: real-world objects, such as ships and credit cards, and abstractions, such as reservations. Entity beans describe both the state and behavior of real-world objects and allow developers to encapsulate the data and business rules associated with specific concepts; an Employee entity encapsulates the data and business rules associated with an employee, for example. This makes it possible for data associated with a concept to be manipulated consistently and safely.

Entities represent data in the database, so changes to an entity bean result in changes to the database. That’s ultimately the purpose of an entity bean: to provide programmers with a simpler mechanism for accessing and changing data. It is much easier to change a customer’s name by calling Employee.setName() ...