RDS Programming Model in Detail

The following are key elements of the RDS programming model:

• RDS.DataSpace
• RDSServer.DataFactory
• RDS.DataControl
• Event

RDS.DataSpace

Your client application must specify the server and the server program to invoke. In return, your application receives a reference to the server program and can treat the reference as if it were the server program itself.

The RDS object model embodies this functionality with the RDS.DataSpace object.

The server program is specified with a program identifier, or ProgID. The server uses the ProgID and the server machine's registry to locate information about the actual program to initiate.

RDS makes a distinction internally depending on whether the server program is on a remote server across the Internet or an intranet; a server on a local area network; or not on a server at all, but instead on a local dynamic-link library (DLL). This distinction determines how information is exchanged between the client and the server, and makes a tangible difference in the type of reference returned to your client application. However, from your point of view, this distinction has no special meaning. All that matters is that you receive a usable program reference.

RDSServer.DataFactory

RDS provides a default server program that can either perform a SQL query against the data source and return a Recordset object or take a Recordset object and update the data source.

The RDS object model embodies this functionality with the RDSServer.DataFactory object.

In addition, this object has a method for creating an empty Recordset object that you can fill programmatically (CreateRecordset), and another method for converting a Recordset object into a text string to build a Web page (ConvertToString).

With ADO, you can override some of the standard connection and command behavior of the RDSServer.DataFactory with a DataFactory handler and a customization file that contains connection, command, and security parameters.

The server program is sometimes called a business object. You can write your own custom business object that can perform complicated data access, validity checks, and so on. Even when writing a custom business object, you can create an instance of an RDSServer.DataFactory object and use some of its methods to accomplish your own tasks.

RDS.DataControl

RDS provides a means to combine the functionality of the RDS.DataSpace and RDSServer.DataFactory, and also enable visual controls to easily use the Recordset object returned by a query from a data source. RDS attempts, for the most common case, to do as much as possible to automatically gain access to information on a server and display it in a visual control.

The RDS object model embodies this functionality with the RDS.DataControl object.

The RDS.DataControl has two aspects. One aspect pertains to the data source. If you set the command and connection information using the Connect and SQL properties of the RDS.DataControl, it will automatically use the RDS.DataSpace to create a reference to the default RDSServer.DataFactory object. Then the RDSServer.DataFactory will use the Connect property value to connect to the data source, use the SQL property value to obtain a Recordset from the data source, and return the Recordset object to the RDS.DataControl.

The second aspect pertains to the display of returned Recordset information in a visual control. You can associate a visual control with the RDS.DataControl (in a process called binding) and gain access to the information in the associated Recordset object, displaying query results on a Web page in Microsoft® Internet Explorer. Each RDS.DataControl object binds one Recordset object, representing the results of a single query, to one or more visual controls (for example, a text box, combo box, grid control, and so forth). There may be more than one RDS.DataControl object on each page. Each RDS.DataControl object can be connected to a different data source and contain the results of a separate query.

The RDS.DataControl object also has its own methods for navigating, sorting, and filtering the rows of the associated Recordset object. These methods are similar, but not the same as the methods on the ADO Recordset object.

Events

RDS supports two of its own events, which are independent of the ADO event model. The onReadyStateChange event is called whenever the RDS.DataControl ReadyState property changes, thus notifying you when an asynchronous operation has successfully completed, terminated, or experienced an error. The onError event is called whenever an error occurs, even if the error occurs during an asynchronous operation.

Note   Microsoft Internet Explorer provides two additional events to RDS—onDataSetChanged (the Recordset is functional but still retrieving rows) and onDataSetComplete (the Recordset has finished retrieving rows).

See Also

RDS Programming Model with Objects | DataControl Object (RDS) | DataFactory Object (RDSServer) | DataSpace Object (RDS) | RDS Tutorial | Using RDS