Overview of the WCF channel model with the SQL adapter

To invoke operations on the Microsoft BizTalk Adapter for SQL Server, your code acts as a WCF client and sends outbound operations to the adapter. In the WCF channel model, your code invokes operations on the adapter by sending a request message over a channel.

To receive polling-based data-changed messages using the adapter, your code acts as a WCF service and receives the inbound Polling, TypedPolling, or Notification operation from the adapter. In other words, your code receives a request message for these operations from the adapter over a channel.

The topics in this section provide an overview of using the SQL adapter with the WCF channel model.

WCF Channel Model Overview

Clients and services communicate by exchanging SOAP messages. The WCF channel model is a low-level abstraction of this message exchange. It provides interfaces and types that enable you to send and receive messages by using a layered protocol stack called a channel stack. Each layer of the stack is composed of a channel, and each channel is created from a WCF binding. At the lowest layer is the transport channel. The transport channel implements the underlying transport mechanism between a service and a client and presents each message to the higher layers (and ultimately the consuming application) as a System.ServiceModel.Message. The WCF Message class is an abstraction of a SOAP message. WCF provides several channel interfaces, called channel shapes, that model the basic SOAP message exchange patterns, such as request-reply or one-way. A WCF transport binding provides an implementation of one or more channel shapes that higher layers can use to send and receive messages. For more information about the WCF channel model, see Channel Model Overview.

The SQL adapter is a WCF custom transport binding that exposes a SQL Server database as a WCF service.

Supported Channel Shapes for the SQL Server Adapter

The adapter implements the following WCF channel shapes:

  • IRequestChannel (System.ServiceModel.Channels.IRequestChannel). The IRequestChannel interface implements the client side of a request-reply message exchange. You can use an IRequestChannel to perform operations for which you want to consume a response, for example to perform a SELECT query on a table.

  • IOutputChannel (System.ServiceModel.Channels.IOutputChannel). This shape implements the client side of a one-way message exchange. You can use an IOutputChannel to invoke an operation for which you do not need to consume a response, for example to call a procedure that has no return parameters.

    Important

    All underlying calls by the adapter to the SQL Server client are synchronous. This includes calls to the SQL Server client that are the result of operations invoked over an IOutputChannel. When you use an IOutputChannel, the adapter discards the response received from the SQL Server client.

  • IInputChannel (System.ServiceModel.Channels.IInputChannel). This shape implements the service side of a one-way message exchange. You use an IInputChannel to receive messages for inbound operations, such as Polling or Notification, from the adapter.

    Like any WCF binding, the SQL adapter uses a factory pattern to provide channels to application code. You use a Microsoft.Adapters.SQLBinding object to create instances of:

  • System.ServiceModel.ChannelFactory<IRequestChannel> to provide IRequestChannel channels you can use to invoke request-response operations on the adapter.

  • System.ServiceModel.ChannelFactory<IOutputChannel> to provide IOutputChannel channels you can use to invoke one-way operations on the adapter.

  • System.ServiceModel.IChannelListener<IInputChannel> to provide IInputChannel channels you can use to receive messages for inbound operations, such as Polling or Notification, from the adapter.

Creating Messages for the SQL Server Database Adapter in the WCF Channel Model

In WCF the System.ServiceModel.Channels.Message class provides an in memory representation of a SOAP message. You create a Message instance by invoking the static Message.Create method.

There are two important parts to the SOAP message that you must specify when you create a Message instance to send to the SQL adapter.

  • The message action is a string that is part of the SOAP message header. The message action identifies the operation that should be invoked on the database. The following shows the message action specified to invoke the Select operation on the Employee table: TableOp/Select/dbo/Employee.

  • The message body contains the parameter data for the operation. The message body is composed of well-formed XML that corresponds to the message schema expected by the SQL adapter for the requested operation. The following message body specifies a Select operation on the Employee table (SELECT * FROM Employee WHERE Employee_ID=10001).

    <Select xmlns="http://schemas.microsoft.com/Sql/2008/05/TableOp/dbo/Employee">  
      <Columns>*</Columns>  
      <Query>where Employee_ID=10001</Query>  
    </Select>  
    

    For information about the SQL adapter message schemas and message actions for operations, see Messages and Message Schemas for BizTalk Adapter for SQL Server.

    This Create method is overloaded and offers many different options for providing the message body. The following code shows how to create a Message instance by using an XmlReader to supply the message body. In this code, the message body is read from a file.

XmlReader readerIn = XmlReader.Create("SelectInput.xml");  
Message messageIn = Message.CreateMessage(MessageVersion.Default,  
    "TableOp/Select/dbo/Employee",  
    readerIn);  

Important

You must provide a message action in your Message instance. This is typically done when the Message instance is created.

See Also

Develop applications using the WCF Channel model