Duplex Contracts in Workflow Services (WF + WCF)

I was just flicking through the pages towards the end of my Workflow Foundation book which I have barely read (I figured maybe they hide all the juicy stuff at the back :D) and noticed something that caught my eye - it said that workflow services, ie workflows hosted in WCF services, cannot use WCF duplex contracts.
This sounds pretty strange to me as I cant understand why that would be the case but can anyone confirm if this is true or if there is any way around it etc as I would like to use both workflow and duplex contracts (they are one of the best parts of WCF!) ?

Cheers
Chris

I think it's possible but it's not usually done because of the way WF works. The reasoning probably went like this: Let's say you have a WF state machine and a duplex method exposing it. Now, how long do you keep the connection between client-service open? The Workflow could take days, months, hours, seconds. You don't know and neither do they, so it's probably not supported, though it must be possible - it is just a method call... I haven't tried this out of course, but give it a shot.

What also might give problems is that a WF that is stopped, could be continued on another machine, so that would make it impossible for the connection

Quote:

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Originally Posted by mendhak

Let's say you have a WF state machine and a duplex method exposing it.

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Oh I didnt mean a duplex method exposing the main WF workflow, I just meant is it not possible to use duplex contracts anywhere within a workflow service. Maybe its just because I have not really familiar with WF yet so I dont understand how it would integrate with WCF so well...

I thought Workflow was basically just a differnt way of designing and viewing your code, rather than it actually affecting what your code can and cant do directly.