user manual

Chapter 18: Generating Entity Bean Primary Keys 191

Chapter

Chapter 18Generating Entity Bean Primary

Keys

Each entity bean must have a unique primary key that is used to identify the

bean instance. The primary key can be represented by a Java class, which

must be a legal value type in RMI-IIOP. Therefore, it extends the

java.io.Serializable interface. It must also provide an implementation of the

Object.equals(Object other) and Object.hashCode() methods.

Normally, the primary key fields of entity beans must be set in the ejbCreate()

method. The fields are then used to insert a new record into the database.

This can be a difficult procedure, however, bloating the method, and many

databases now have built-in mechanisms for providing appropriate primary

key values. A more elegant means of generating primary keys is for the user

to implement a separate class that generates primary keys. This class can

also implement database-specific programming logic for generating primary

keys.

You may either generate primary keys by hand, use a custom class, or allow

the container to use the database tools to perform this for you. If you use a

custom class, implement the com.borland.ejb.pm.PrimaryKeyGenerationListener

interface, discussed in “Generating primary keys from a custom class” on

page 192. To use the database tools, you can refer to “Implementing primary

key generation by the CMP engine” on page 192 for information on the CMP

engine generating primary keys depending upon the database vendor.

Important For documentation updates, go to www.borland.com/techpubs/bes.