The persistentAllowed class option enables you to specify that a class can have persistent instances. (For details, see "Adding Classes to Your Schema", in Chapter 3.)
If you uncheck the Allow Persistent Instances check box on the Lifetime sheet of the Define Class dialog, an exception is raised at every attempt to create a persistent instance of the class. An error is raised if you attempt to construct a persistent object from within a method (that is, you call create <object-name> persistent).
Persistent instances of subclasses are restricted according to the subclassPersistentAllowed class option, described later in this section.
When you create a new class, the default setting for the persistentAllowed class option is determined as follows.
The default value is the same as the subclassPersistentAllowed option value of the immediate superclass.
If the subclassPersistentAllowed option of the immediate superclass is set to false, the Allow Persistent Instances check box on the Lifetime sheet of the Define Class dialog is disabled.
You cannot set the persistentAllowed option to false for a class where persistent instances of the class exist. You must delete these instances before the change is made.