References (WMI)

The MOF ref key word describes an object path and maps to a VT_BSTR Automation type. The object path can be either a full path to a server and namespace, or a relative path to another object in the same namespace. You can use a ref key word to link two or more classes together. WMI supports two types of object paths, which use to define general or specific paths within WMI.

The main purpose of the ref key word is to reduce transport time and encoding between objects that exist entirely within the WMI repository. You can also use the ref key word to create an association between two classes. For more information, see Declaring an Association Class. If the referenced item is located within the same MOF file, use an alias to initialize the ref value. For more information, see Creating an Alias.

MOF supports the concept of a weakly typed and strongly typed object path. A weakly typed object path points to an object of an unspecified class and uses the ref key word with the OBJECT keyword. A strongly typed object points to an object of a specific class and uses ref with the class name. The following example describes a weakly typed RefToAnyClass reference that can point to any class or class instance, and a RefToClassX reference that can point only to a ClassX class or instance:

class MyClass
{
    object ref RefToAnyClass;       // Weakly typed
    ClassX ref RefToClassX;         // Strongly typed
};

The following example describes two instances and an association object that references the previous instances:

#pragma namespace("\\\\.\\root")

instance of __Namespace
{
    Name = "WMI" ;
} ;

#pragma namespace("\\\\.\\root\\WMI")

Class A{
    [key] string aKey;
};

Class C{
    [key] string cKey;
};

// The following class creates an association 
// between the "A" class and the "C" class
    [Association] Class B{
    [key] A ref aRef;
    [Key, Min(1)] C ref cRef;
};

instance of a
{
    aKey = "This is the key for the A class";
};

instance of c
{
    cKey = "This is the key for the c class";
};