<on-exit> and exception handling

[habuma]

Let's say that I have a state that looks a little something like this:

<view-state id="A">
  <transition on="condition1" to="B" />
  <transition on="condition2" to="C" />
  <transition on="condition3" to="D" />
  <on-exit>
    <evaluate expression="someService.someAction()"/>      
  </on-exit>
</view-state>

Here I have a state that could end up transitioning to one of 3 other states. But regardless of where I head off to next, I need to always invoke someService.someAction()...that's why it's in <on-exit>.

Fine...but what if someService.someAction() throws an exception? In that case I'd like to transition to "E"...so I change the state to this:

<view-state id="A">
  <transition on="condition1" to="B" />
  <transition on="condition2" to="C" />
  <transition on="condition3" to="D" />
  <transition on-exception="SomeException" to "E" />
  <on-exit>
    <evaluate expression="someService.someAction()"/>      
  </on-exit>
</view-state>

And this is where it all goes pear-shaped. As I transition away from "A", an exception is thrown from someService.someAction(). That triggers the on-exception transition...which is a transition away from "A", which means that the <on-exit> block is executed. someService.someAction() still throws an exception, which triggers the on-exception transition...which is a transition away from "A", which means...

You get the picture.

I read elsewhere that it is recommended to let exceptions be handled in the service and to have the service return an event for SWF to transition from. I agree with that...but not sure that it helps me here because I'd end up with the same scenario, only without the exceptions.

Any idea how I can make this work?

[InverseFalcon]

It's redundant, but can you put your on-exit expression inside each of the transitions instead? This should let your on-exception transition work properly.

[habuma]

That would work except that I left out one little detail (for simplicity's sake...I didn't think it would matter at the time)...

Some of those transitions are defined in a parent state and are inherited by a handful of other states. The following snippet better illustrates the scenario I'm looking at:

<view-state id="#SOME_SECTION">
  <transition on="condition2" to="C" />
  <transition on="condition3" to="D" />
</view-state>

<view-state id="A" parent="#SOME_SECTION>
  <transition on="condition1" to="B" />

  <transition on-exception="SomeException" to "E" />
  <on-exit>
    <evaluate expression="someService.someAction()"/>      
  </on-exit>
</view-state>

<view-state id="Z" parent="#SOME_SECTION>
  <transition on="condition1" to="B" />

  <transition on-exception="SomeException" to "E" />
</view-state>

Here, I need to call someService.someAction() whenever/however I transition away from "A". But I do *NOT* need to call it when transitioning away from "Z".

I suppose that I could create multiple parents (one with and one without the on-exit), but that is a bit uglier than I would've liked.

[InverseFalcon]

Remember, transition elements are merged, they don't override.

You can redefine all of the inherited transitions in state "A" and place your evaluate expression in each of the transitions.