What's New in Windows Workflow Foundation in .NET 4.5?

Part I
During the last //build/ conference a number of new WF4, or should I now say WF4.5, features where announced. While the list of new features isn’t earth shattering long some of the most annoying shortcomings where addressed.

Designer enhancements

As a developer I spend a lot of time in the designer so any improvements there are going to make me happy. And I am very happy to see some of the new features.

Auto surround with a Sequence.

This seemingly small feature is a real time saver. There are lots of places where an activity has a child activity to execute, for example an If activity has a Then and an Else and executes either. These are of type Activity so by default you can add a single activity there. At runtime this is no problem. Want multiple child activities? Just add a Sequence and you can add as many child activities as you want. The problem is that in the designer that means removing the existing child (you can put it on the clipboard), adding a sequence and finally re-adding the original child. Not difficult but somewhat cumbersome and I never like deleting something I need and saving it on the clipboard.

No longer.  Now we can just drag a new Activity and the designer will automatically wrap the existing activity in a Sequence. So much easier and a much nicer way to work!

Annotations

Another feature I missed greatly was adding comments to an Activity describing its intent. All we had was the DisplayName and that was not much of a replacement. Fortunately we now get Annotations allowing us to add more information about the intent.

Search

Searching through workflows is another big one. With small workflows it is quite easy to see where a variable is used but when workflows get bigger this becomes an increasingly hard problem. With WF4 I typically solve this by opening the workflow XAML in a text editor and searching the raw XML. While this works reasonably well it is less that perfect and one of those tricks you need to pick up while working with WF4. The new search capability will let you search through a workflow in the designer, as you really should, just as any other Visual Studio artifact. Another great improvement.

Multi-select of activities

As soon as you start creating flow chart or state machine workflow you will quickly find you have to rearrange the existing activities to make place for a new one. Seems simple enough to move them right? Well you are wrong as the designer only lets you select a single activity at the time so you can’t move a group of them in one go.

Well no longer as we can now select multiple activities and drag them around as a group.

This is by no means the complete list of changes, here you can find a more complete list, but these are the ones I think most people, myself included, where really missing. Glad to see them being added, now if only we could get to work with them today.

Part II
During the last //build/ conference a number of new WF4.5 features where announced. In part 1 I took a look at the designer improvements, here I am going to take a look at some of the runtime enhancements.

Runtime Enhancements

New activities

As part of WF 4.5 we will see some new activities in the box. The number isn’t earth shattering but as I always tell people WF activities are all about your business and Microsoft can’t create activities tailored to your business, you need to do so yourself.

One useful new activity is the NoPersistScope. Not that it is very hard to create yourself once you know how, I wrote a blog post about it here, but not easy to discover and certainly something that is very useful.

State machine

Although not completely new, it was released as part of the .NET 4 platform update 1, the state machine is now rolled into the .NET framework proper so it doesn’t require an additional install. Nice to see that back.

C# Expressions

One thing a lot of developers are going to be very happy with is support for C# expressions. Previously you where forced to use VB expressions, even in a C# project. And while that isn’t extremely hard it did require a mental switch and, as most C# developers aren’t fluent in VB, some frequent searching for the right syntax. With WF 4.5 you can enter you expressions using the C# syntax in a C# project and in VB syntax in a VB project. So much better.

Besides C# expression it appears we can also replace the expression authoring experience with something we control using new extensibility points in the designer. So far I have not seen any details of this so I am curious to what kind of scenarios this opens up.

Versioning

The most important new feature is workflow versioning. In Part III - I will go into details on what this new feature brings us.

Part III

This section is about one of the biggest missing pieces which is versioning workflows.  See also part I about the designer enhancements and part II about the other runtime enhancements.


Versioning Workflows
 
To understand why this is so painful at the moment it is important to remember that workflow instances often run for a long time. And that is not just a long time in computer terms, like a few minutes, but a long time in human terms like weeks, months or even years.
Right not with WF4 you can’t change the definition of a workflow instance that is running even when it is persisted to disk. Doing so will result in any number of weird exceptions when the workflow tries to resume. And the fact that you can’t change the definition means you can’t fix a bug, all you can do is let the workflow run and make sure that new instances are started with a fixed definition. Not the nicest of situations and I am very glad this is being addressed.

The first part is the ability to add a version to a workflow instance using a WorkflowIdentity object. This doesn’t fix the versioning issue itself but at least we get a predictable exception.

The second part if the capability to create update maps and update the state of a persisted workflow instance to a newer version. This capability gives us a lot of control as we can choose which workflow instance we upgrade and which we keep at the current version. Basically we create a DynamicUpdateMap and use the DynamicUpdateServices.PrepareForUpdate() to update a workflow instance state. A great and long awaited addition to the workflow runtime.

The final versioning piece is an addition to the WorkflowServiceHost allowing it to host multiple versions of a workflow. This is something we can now achieve using the WCF routing service but is far from trivial to implement. This should make the scenario of versioning workflow services much easier.