Better ability to introspect flow transitions [SWF-43]

[spring-operator]

Chris Wood opened SWF-43 and commented

It would be handy if flow transitions had a bit more information available for introspecting.

This is my use case: In my view I run through the list of available transitions out of the particular view state. I'd like to render these as a list of links / submit buttons / whatever on the page, however there's no way to determine the eventId that the particular transition has as it's criteria, so I can't write the 'eventId' parameter easily.

A related issue is that it would be nice to have a canExecute method on the transition which takes a request context (for the current view state) and an eventId (for what view we're going to go to). Why is this useful? Again for the above case where we're running through the list of transitions and determining which ones are valid for this current view. The criteria list could then contain criteria based on security permissions ect.

I'd be happy to implement this bit of functionality and contribute it back if someone gives me the nod.

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No further details from SWF-43

[spring-operator]

Erwin Vervaet commented

First, we can't easily provide a 'getEventId' method on the Transition class since it's the matching TransitionCriteria that are responsible for transition matching and there is no guarantee that you're using an EventIdTransitionCriteria. If you are using a EventIdTransitionCriteria, you could do:

Transition t = ...;
String eventId = ((EventIdTransitionCriteria)t.getMatchingCriteria()).getEventId();

In JSP EL the casting would go away so you'd be able to do ${transition.matchingCriteria.eventId}. That seems reasonable.

Secondly, the transition class already has a matches(RequestContext) method. An easy way to get the behaviour you want is to write a RequestContextWrapper that delegates all calls except for getLastEvent() to the wrapped RequestContext. The getLastEvent() method just returns the event you'd like to test.