With application identity you are taking control of the specification of id's to JPOX. Application identity
requires a primary key class (unless using SingleFieldIdentity, where one is provided for you), and each persistent
capable class may define a different class for its primary key, and different persistent capable classes can use the same
primary key class, as appropriate. With application identity the field(s) of the primary key will be present as field(s)
of the class itself. To specify that a class is to use application identity, you add the following to the MetaData for
the class.
<class name="MyClass" identity-type="application" objectid-class="MyIdClass">
<field name="myPrimaryKeyField" primary-key="true"/>
...
</class>
That is, specifying the identity-type and objectid-class. The objectid-class is the class defining the identity
for this class. You define the identity of the class using a Primary Key class.
When you have an inheritance hierarchy, you should specify the identity type and any primary-key fields in the
base class for the inheritance tree. This is then used for all persistent classes in the tree.
Using application identity requires the use of a Primary Key class. In JDO 1.0 it was necessary to always
provide this class. In JDO 2.0 an in-built class is available where the identity is defined in a single field.
This is referred to as SingleFieldIdentity. JPOX supports this builtin class. Where the class has multiple
fields that form the primary key a Primary Key class must be provided.
See also :-
By choosing application identity you are controlling the process of identity generation for this class. This
does not mean that you have a lot of work to do for this. JDO 2 defines many ways of generating these identities
and JPOX supports all of these and provides some more of its own besides.
See also :-
When using application identity, the class has associated field(s) that equate to the identity. As a result
you can simply access the values for these field(s). Alternatively you could use a JDO identity-independent way
Object id = pm.getObjectId(obj);
Object id = JDOHelper.getObjectId(obj);
JDO allows implementations to support the changing of the identity of a persisted object. This is an optional feature and
JPOX doesn't currently support it.
