Introduction

An ADSI extension is a special COM object that provides a way for developers to extend an ADSI object. Each extension is associated with a specified class in the directory. Developers can give more dynamic meaning to an object by adding methods. In a traditional directory-programming model, objects are accessed by setting and getting properties or attributes.

An extension writer will implement a method that provides additional behavior not initially supplied by the IIS ADSI provider. For example, a company that backs up and restores software wants to extend an ADSI object by creating two methods called BackUp and Restore. These methods will operate remotely on the physical computer pointed to by the ADSI object. By participating as an extension, the methods automatically gain access to the ADSI infrastructure and are viewed by ADSI clients as an integral part of the IIS ADSI provider.

Do I need a custom extension?

Not all components are appropriate as an ADSI extension. The following guidelines should help you decide if creating an ADSI extension is necessary. Create an extension to:

• Simplify tasks. This is the most common use of the extensibility model. Many tasks in the directory can be accomplished by searching for and setting multiple attributes or properties in one or more objects.
• Integrate your component with the IIS ADSI provider object. You can create an ADSI extension that will populate fields in a SQL Server database every time a Web site is created.
• Provide a directory lookup for your component. Your component can require a directory as a starting point for directory look up. For example, if you are creating a new application object named MyNewApp, it can be published as an extension object in the metabase. In this case, MyNewApp is designed to support status notifications to a collection of servers. You decide to make MyNewApp support an ADSI extension method called NotifyNow, which will provide additional information about each occurrence of MyNewApp in the metabase (for example, getting the server names and notifying each server).
• Provide a junction point between namespaces and programming models. For example, you could invent a new object model for Web services, called WebServices. The default UserAccount object exists in the default namespace. You can create an ADSI extension within WebServices and associate it with the UserAccount object. The ADSI user will be able to bind to a UserAccount object and use the new WebServices object model. From the ADSI client’s perspective, this junction point is transparent.

What are the benefits of using ADSI extensions?

ADSI extensibility enriches the programming environment in many ways:

• Easy implementation. Extensions are easy to implement. With existing Microsoft technology, Visual C++^™ and the Active Template Library^™, one can develop extensions in a short time.
• Quick start for programmers. Independent extension writers can extend the ADSI Interface without prior knowledge of all existing extensions.
• Builds on existing ADSI model. IIS ADSI programmers do not have to learn a new programming model. The extensions become part of ADSI.
• Customizable. IIS administrators can manage related ADSI applications through custom extensions. Existing IIS ADSI components can be integrated by the use of extensions, to meet specific needs.
• Simplified handling of IDispatch. Clients view one IDispatch. From the script and automation writers perspective the extension methods and properties are part of the IIS ADSI programming model.

Consider the following hypothetical scenario. A network administrator wants to automate a backup procedure for each of her sites. She can accomplish this by writing an extension for the IIsWebService object that includes a backup method. She chooses to call her new method BackUp. She has also created a new property called LastBackUp. The following code is an example of how to call the BackUp method:

Dim objExt as IADsContainer
Set objExt = GetObject("IIS://W3SVC/")
objExt = Array("IIsWebService")
For Each item in objExt
   Debug.Print item.Get("ServerComment")
   Debug.Print item.LastBackUp
   item.BackUp
Next
 

LastBackUp is a custom property provided by the extension writer, which stores a time and date stamp; BackUp is a custom method provided by the extension writer, which backs up the object represented by item to an archive specified by the administrator.

The preceding code fragment illustrates the benefits for both clients and providers. The extension writer does not have to reinvent a new way of filtering, searching, and accessing the directory. The extension consumer, on the other hand, does not have to relearn a new programming paradigm. New methods and properties provided by the extension writer are viewed as if they are part of ADSI.