Business rules involving parent/child objects

[Chicagoan2016]

This is related to #4653. I didn't want to hijack that thread.
We have several scenarios where the second pattern described in #4653 could help.
We have to validate certain properties that are part of the child object, but we want to do it in the parent object.
The big reason is the design of our current UI.
Would love to discuss this use case here.

Kind Regards

[rockfordlhotka]

This is an area that could use some improvement in CSLA for sure.

However, the mechanism exists to do this through the ChildChanged events. The parent can handle the ChildChanged event, and the args parameter to that event provides info about exactly what changed lower in the graph. This allows your code in the event handler to call the appropriate CheckRules method based on what changed.

There are two areas I think can be improved.

The big one is that we need a way where you can call CheckRulesAsync safely. That doesn't exist today, and is a hole that needs to be addressed. You can call the method, but any exceptions would be invisible, and that's a problem.

The second area for improvement, is that I'd like a better abstraction for this so you don't need to write the ChildChanged handler code. It would be better if you could somehow register rules to run when children change. That's not simple, because we need a way to do BusinessRules.AddRule that doesn't just attach a rule to a property, but attaches a rule to conditional changes to some child and/or child property lower in the graph.

Now that I type out that requirement, I wonder if we can't do that by allowing you to provide a lambda as a parameter to AddRule, so you can provide that conditional check. That might be a workable solution.