JDO Predefined ID Classes
An object ID is a combination of a persistence capable class and a primary key. It provides a unique representation of a persistent object.
The following classes serve as predefined ID classes for persistence capable classes with a simple single field primary key:
- javax.jdo.identity.ByteIdentity
- javax.jdo.identity.CharIdentity
- javax.jdo.identity.IntIdentity
- javax.jdo.identity.LongIdentity
- javax.jdo.identity.ObjectIdentity
- javax.jdo.identity.ShortIdentity
- javax.jdo.identity.StringIdentity
- javax.jdo.identity.SingleFieldIdentity
Object IDs are used in many PersistenceManager methods (getObjectId, getObjectById, getObjectByIds, etc.) to represent objects but should not be used as the type of a primary key field in a persistence capable class.
For example, to use a String primary key define a primary key field of type String:
@PersistenceCapable public class MyClass { @PrimaryKey String id; }
Persistent objects with a String primary key (including instances of MyClass) can be represented uniquely by StringIdentity, as a combination of a class and a string value.
