Keyvan Nayyeri

In one of my recent posts I discussed about Invoking a WebService from a Workflow.  The other case is when you want to build a webservice that runs a workflow to return its results.  This is the topic of this post but is a little harder than invoking a webservice from a workflow.

Create the Workflow

Before anything we need a workflow to expose it via our webservice.  This step is the main step in building the webservice.  First I create a new Sequential Workflow Library project to build my workflow.  This workflow does the same job as what my webservice in previous post does: getting a birthdate and returning the age.

There are three built-in workflow activities in Windows Workflow Foundation that play role in building this type of workflows: WebServiceInput, WebServiceOutput and WebServiceFault.  In my sample I won't use the last one (WebServiceFault) but it's an activity that you can use to handle any exceptions thrown by your webservice.

WebServiceInput and WebServiceOutput are a pair of activities.  First one gets the parameters and second one returns the result (if there is any return value for web methods).

In addition to Name, WebServiceInput has some required properties:

• InterfaceType: The type of the service interface.  It will be described later.
• IsActivating: Specifies that if this WebServiceInput is activating the service.  For first WebServiceInput activities in a workflow it must be set to True.
• MethodName: Name of the web method that we're going to implement.
• Method Parameters: Zero, one or more input parameters based on what we have defined in our interface.

WebServiceOutput has a few required properties as well:

• InputActivityName: Name of the corresponding WebServiceInput activity.
• ReturnValue: Return value of web method if method has any result.

So now I should create an interface for my service.  This interface is very simple.  You can remember same thing from WCF services, can't you?!

After this I can step into adding a WebServiceInput to my sequential workflow.  I click on "..." button beside InterfaceType textbox to open up "Browse and Select a .NET Type" dialogue.  Here I choose IService interface and click on Ok.  Next step is to choose the name of my web method (GetAge) from MethodName drop down list.  I also must set IsActivating property to True.  This is required for first WebServiceInput activity in a workflow.  The last step to configure my WebServiceInput is to create a new birthDate member for BirthDate property to keep the value of BirthDate input parameter.  This will add an auto-generated code for birthDate member to my workflow code.

Now it's time to add a WebServiceOutput activity to my sequential workflow.  After adding this new activity I choose the name of my WebServiceInput activity as value for its InputActivityName property from drop down list and create a new member (named age) for ReturnValue property.  This will add an auto-generated code to my workflow code for age member.

After this I have to add my code logic for my GetAge() method.  There are two ways to do this:

• I can add as many as other activities to workflow that I like and implement my logic inside them.  I'll do this and will add a Code activity to implement my simple logic.
• I can also use two events from WebServiceInput and WebServiceOutput activities to implement my logic inside them.  WebServiceInput has an InputReceived event that raises after that webservice receives its parameters and WebServiceOutput has a SendingOutput event that raises before returning the result from the webservice.  It's also possible to implement the logic inside these events after WebServiceInput and before WebServiceOutput.

I'm going to implement the first choice so add a Code activity to my workflow and add my simple logic to its execution.

So finally my sequential workflow looks like this:

And final code is this:

Now I build my solution to create an assembly and use it in next steps.

Create the Service

Now that I have the workflow for my webservice as an assembly I can create my webservice easily.  First I create an ASP.NET Web Service project for my webservice then add three references to my workflow assembly, System.Workflow.Runtime (to be able to run workflow engine inside my webservice) and System.Workflow.Activities (to be able to run workflow activities inside my webservice).

After adding these references, I create a new service but don't use its default implementation (derived from System.Web.Services.WebService).  Instead, I derive this service from my workflow (after building the assembly an "_WebService" prefix is added to my class name).  I don't add anything else to this service.  As it's derived from my workflow it inherits the service behavior from the base class.

The last step is to configure my service.  I need to add a default Windows Workflow assembly to my HttpModules to manage workflow hosting.  System.Workflow.Runtime.Hosting.WorkflowWebHostingModule does this job for me.  On the other hand I add a reference to System.Workflow.Runtime.Configuration.WorkflowRuntimeSection inside my <configSections /> element.  Configurations for adding the required assemblies to Web.Config are done automatically under <compilation /> element.

At this point my webservice is ready for testing. 

Test the Service

At the end I test my webservice to see if it works.

Now playing: Yanni - Tribute