ADSI and Extensions: What's Happening Under the Hood?

This is how ADSI interacts with extensions.

• Something binds to an ADSI directory object. For example, LDAP://CN=Jsmith, OU=Sales, DC=Microsoft, DC=COM.
• ADSI finds that the object is in the class called user.
• ADSI does a lookup in the registry and finds the extension CLSIDs for user. (Note: ADSI actually caches this information.)
• Something calls the QueryInterface method for IID_IMyExtension. ADSI searches the interfaces associated with the user object, starting with its own interfaces, then looking at extension interfaces.
• If a match is found, ADSI creates an instance of the component that supports IID_IMyExtension, and calls QueryInterface for the extension. The resulting interface is returned to the consumer.
• The consumer uses this interface to call the interface's methods.
• Next, the client calls QueryInterface for IID_IYourExtension, which is in a different component. This component will delegate this QueryInterface call to the IUnknown interface of the aggregator, which happens to be ADSI itself.
• Once again, ADSI searches the interfaces and creates the component instance.