web server - Borland Technical Publications

Chapter
18
18Generating Entity Bean
Chapter
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 164. To use the database
tools, you can set properties for the CMP engine to generate primary keys depending
upon the database vendor. See “Implementing primary key generation by the CMP
engine” on page 164.
Generating primary keys from a user class
With enterprise beans, the primary key is represented by a Java class containing the
unique data. This primary key class can be any class as long as that class is a legal
value type in RMI-IIOP, meaning it extends the java.io.Serializable interface. It must
also provide an implementation of the Object.equals(Object other) and
Object.hashCode() methods, two methods which all Java classes inherit by definition.
Chapter 18: Generating Entity Bean Primary Keys 163