Using Caché Objects - InterSystems Documentation

A class inherits all of the specifications of its superclasses, including properties, methods,
class parameters, applicable class keywords, and the parameters and keywords of the inherited
properties and inherited methods. Except for items marked as Final, the subclass can override
(but not delete) many of the characteristics of its inherited components.
In addition to a class inheriting methods from its superclasses, the class' properties inherit
additional methods from system property behavior classes and, in the case of a data type
attribute, from the data type class.
For example, if there is a class defined called Person:
Class MyApp.Person Extends %Persistent [ClassType = persistent]
{
Property Name As %String;
Property DOB As %Date;
}
It's simple to derive a new class, Employee, from it:
Class MyApp.Employee Extends Person [ClassType = persistent]
{
Property Salary As %Integer;
Property Department As %String;
}
Inheritance
This definition establishes the Employee class as a subclass of the Person class. In addition
to its own class parameters, properties, and methods, the Employee class includes all of these
elements from the Person class.
Note:
A class does not inherit the value of its superclass' ClassType keyword. You must
explicitly specify this value in every subclass.
You can use a subclass in any place in which you might use its superclass. For example, using
the above defined Employee and Person classes, it is possible to open an Employee object
and refer to it as a Person:
Set x = ##class(MyApp.Person).%OpenId(id)
Write x.Name // results in "Groucho Marx"
We can also access Employee-specific attributes or methods:
Write x.Salary // results in 22000
Using Caché Objects 21