To overcome this limitation and to call a WCF service from SQL I thought upon the alternatives available. I came across the SQL CLR functionality.

I found that to invoke a web service from SQL (through SQL statements and stored procedures), understanding the capabilities of SQL CLR and exposing a .NET method as a CLR Stored Procedure is very essential.

SQL Server 2005 integration with CLR

Microsoft SQL Server now features the integration of the common language runtime (CLR) component of the .NET Framework for Microsoft Windows. The CLR supplies managed code with services such as cross-language integration, code access security, object lifetime management, and debugging and profiling support. For SQL Server users and application developers, CLR integration means that developers can now write stored procedures, triggers, user-defined types, user-defined functions (scalar and table-valued), and user-defined aggregate functions using any .NET Framework language, including Microsoft Visual Basic .NET and Microsoft Visual C#.

Creating a WCF client

To consume a WCF service through SQL, we need to create a client proxy for the WCF service. The steps involved in creating a client are

• Obtain the service contract, binding, and address information for a service endpoint.
• Create a WCF client using that information.
• Call operations.
• Close the WCF client object.

The above steps are sufficient in order to call a WCF service from a .NET managed application. However to invoke the WCF from a SQL statement or Stored Procedure the following additional steps are required

• Expose a public static method which in turn calls the WCF service
• Decorate the static method with SqlFuntion attribute, as below

[SqlFunction(FillRowMethodName = "FillRow", DataAccess = DataAccessKind.Read)]

• Provide a FillRow method. The FillRow method acts as a helper method which fills in a row of the result set returned by the table valued function. FillRow method is the place to handle Null values and gives the developer a chance to pass an appropriate value in case the actual result returned by the client is null.
• At the command prompt CD to the output directory and execute the sgen command. This creates the <wcf_client_assembly_name>.XmlSerializers.dll library necessary to avoid dynamically generating the serializers used during the invocation of the web service.

Exposing a WCF client as a SQL CLR Function

To load the WCF client assembly into SQL, the below steps need to be followed

• Enable CLR on SQL by executing the following statement

  EXEC sp_configure 'clr enabled', 1

  RECONFIGURE WITH OVERRIDE;

• Set the database Trustworthy to ON

  ALTER DATABASE <database name>

SET TRUSTWORTHY ON

• Create the assembly in SQL by using the CREATE Assembly statement as below. Note the use of PERMISSION_SET = UNSAFE. This is required since the CLR based stored procedure bas to cross the database boundary and access external resources.

  CREATE ASSEMBLY <WCF_Client_Assembly_Name>

  FROM <Fully Qualified Path to the assembly file>

  WITH PERMISSION_SET = UNSAFE

• Expose the static method in the assembly (uploaded in the previous step) as a SQL Function, like below

  CREATE FUNCTION <CLR Function Name>(<parameters to the WCF client function)

  RETURNS TABLE

  (

  <return values with data type>

  )

AS EXTERNAL NAME <WCF_Client_Assembly_Name>.<WCF_Client_Class>.<Method>;

Additional links

Introducing SQL Server 2005's CLR Integration - https://www.devsource.com/print_article2/0,1217,a=151093,00.asp

CLR Integration Programming Model Restrictions - https://msdn2.microsoft.com/en-us/library/ms403273.aspx

What is Windows Communication Foundation - https://msdn2.microsoft.com/en-us/library/ms731082.aspx

Workflow Runtime

To execute a Workflow, create an instance of WorkflowRuntime like below

WorkflowRuntime workflowRuntime = new WorkflowRuntime()

WorkflowRuntime is a class under System.Workflow.Runtime namespace in system.workflow.runtime.dll. As you would assume WorkflowRuntime abstracts out the functionality of creating, hosting and managing multiple workflows.

A Workflowruntime can host, execute and manage multiple workflows simultaneously. All this is done by executing each workflow hosted, on a different thread. Since multiple threads are getting executed, each thread can complete its execution at its own time, these threads needs to be synchronized. Even if a WorkflowRuntime is hosting and executing a single workflow, the main thread on which WorkflowRuntime is getting executed and the thread (spawned by WorkflowRuntime) running to execute the workflow needs to be synchronized.

AutoResetEvent class comes handy to synchronize threads. All a developer need to do is to create an instance of AutoResetEvent class, and call Set and WaitOne methods on the object. The WaitOne methods lets an executing (main) thread to wait for a spawned thread to complete its execution. The spawned thread calls Set method to indicate the completion of its execution.

AutoResetEvent waitHandle = new AutoResetEvent(false);

workflowRuntime.WorkflowCompleted += delegate(object sender, WorkflowCompletedEventArgs e)

{

waitHandle.Set();

};

Now we have all the stage set to create an instance of a workflow and execute it. WorkflowRuntime has a method CreateWorkflow which takes the workflow type as an argument to create a workflow instance.

// Get the workflow type

Type type = typeof(SimpleWorkflow);

// Create and start an instance of the workflow

workflowRuntime.CreateWorkflow(type, parameters).Start();

        // Wait for the workflow to complete execution

waitHandle.WaitOne();

That's it. That's all is needed to host a Workflow. Isn't it simple?J

Real World scenarios

Though hosting WorkflowRuntime with console applications is simple, it's not the only way. Enterprise systems need a better way to host and manage WorkflowRuntime. Microsoft has thought about this and has come-up with different ways of hosting WorkflowRuntime.

Hosting Workflows in ASP.NET Applications

If you want your application to have a Web interface, you can host your workflows within an ASP.NET application.

Use the WorkflowRuntime object to access the workflow runtime. Applications require one instance of the workflow runtime for all the users of the application. It is possible to create this in the Application_Start event in the Global.asax file.

Use the Web.config file to configure the runtime.

If you use the WorkflowWebRequestContext object to access the workflow runtime, you cannot add services such as persistence or scheduling services because the workflow is already started. If you try to add services to the runtime when it has already started it will generate an error. Instead, to configure the runtime with services, use the <workflowRuntime> section in the Web.config file:

[Web.config]

<configuration>

<configSections>

<section name="WorkflowRuntime"

type="WorkflowRuntimeSection, System.Workflow.Runtime" />

</configSections>

</configuration>