Question

I’m trying to model a request submission/ approval /completion scenario. I’m using a flowchart workflow hosted as a service in a console app using WorkflowServiceHost. The workflow has a service reference to a WCF Service hosted in IIS this second service interacts with the application database. I have an aspnet front end with a service reference to the hosted workflow service and call its methods from a proxy client.

The workflow is using a persistence database that I have created using the scripts provided.

The scenario is that a request for a service is made by a user. The request must be approved once by a specific person (I’m using a pick with a delay in one branch to remind the person if no decision arrives, the other branch is receive decision). For some services the request must have a second approval which can be done by any one of a pool of approvers. Once approval is all finished the request goes to a different pool of people for completion.

I have it working but 3 questions:

1. In the aspnet home page I have a list of requests with links to pages to approve/complete as appropriate and call methods on the proxy after which they redirect back but because it’s all asynchronous I am having to manually refresh the home page to see the changed list. Am I stuck with forcing the page to refresh itself every x seconds to get around this or is there a way to make it synchronous/check state of workflow/wait for a message back? It’s not terribly interactive just hitting a button and not knowing whether the action succeeded or not.
2. Is there a way to stop someone approving a request just after someone else in the pool has approved it? At the moment nothing happens for the second person when they hit the button (which is good). In the workflow persistence database I can see that the blocking bookmark is the next activity along (presumably set by the person who got there first) so it looks as though the second receive just doesn’t happen. I have concurrency checking code in the WCF data service but this never fires because there is no attempt to update the database. I would like to be able to warn the second person that another user got there first.
3. My homepage list in the web app is built by querying the application database, but is it possible to query the workflow to find the status of each item, passing the item’s id (I’m using the id as the correlation handle)? Is it normal to do this or do people usually just query the application database?

Answer 1

1. I guess you could create an Ajax call that would check if any state change occurs and only refresh the page when that is the case.
2. If you send a WCF request for an operation that is no longer valid you should receive an error, unless you are using one way messaging because there is no message to send the error back. Mind you that due to a bug in WF4 the message could be a timeout after 60 seconds. There is no real way to avoid the problem because you are checking the workflow state as persisted and letting the user do an action based on that. Even when you query the state the workflow could have been resumes but not saved yet.
3. Either can work but I normally query the workflow instance store as that is the closest to the actual workflow state.