About RDS Customization Handlers

The combined CML/LitCrit application accesses SQL Server information in a new way, in addition to the database access methods of the original CML application. This new way is called an RDS customization handler (or just handler). An RDS handler is a COM object that resides on the Web server, and is made available when ADO is installed during the installation of Microsoft SQL Server 7.0.

Using the customization (.ini) file of the RDS handler, you configure most of the information RDS requires, including a named connection string (which can include a "DSN=") and a list of users with permissions. You can use the name of the connection string in RDS calls made from the client computer, while storing the details of the connection in the customization (.ini) file on the server. This separation provides additional security. See Advantages of Using Handlers.

Similarly, you can store a query in the customization file and later call the query by name to execute it; this also lets you substitute parameters to make the query more flexible. This mechanism resembles that of stored procedures, but differs in that handler queries are not precompiled or stored in the database, which means that they are not optimized for speed.

Note  The RDS customization handler technology became available with ADO 2.0, which shipped in SQL Server 7.0, and with an ADO 2.0 update, available separately.

You need merely to write the code for Visual Basic® objects (in this case, the Collection object and the FoundTitles objects), specify the name for connection string, and later supply the details of the connection string in the handler's .ini file.

Advantages of Using Handlers

• Handlers provide flexibility. Because the DSN can change, it is changed in the INI file (see The Handler Customization File. ). You can therefore change it whenever needed without having to recompile any code. This means you can change configuration settings after the application has been deployed. The Connection, User, and Query information is stored in a name that we can refer to from the client side. Because DSN can change you can store it in a text file without giving any details away. This text file is stored in a system location that people don't normally have access to.
• Handlers provide security (1). The DSN is stored in the .ini file on the Web server, not in ASP code. This is more secure because it, along with other details of the connection and query, is stored in a system file that users normally have no access to.
• Handlers provide security (2). You can assign permissions to individual user names in the Microsoft Exchange Server directory.
• Handlers provide logs for troubleshooting. Handlers automatically produce a log file that helps you troubleshoot errors. You specify this log file in the section of the handler configuration file. For more information, see Using RDS Handlers.

For more information see the document http://www.microsoft.com/data/ado/rds/custhand.htm.

Disadvantage of Using Handlers

The code used in a handler is not precompiled. It is interpreted at run time, so it is slower than, for example, a stored procedure.