Hi, In my user interface, I can have the user edit a field on an object, and behind the scenes this will trigger a cascade of other changes to other objects. As a result, I don't just need to validate the value the user typed in, I also need to validate all of the other changes that that single edit will make to all of the related objects.
And I cannot come up with a good way to do it. Let's say I have an Employee object (with a "name" attribute, a title, a salary, and a related department), and a Department object (also with a name, and a list of related employees). In the interface, I add in a new user, "Jenkins", say he's a "Developer", who makes $100k, and add him into the "IT" department. This passes all the constraints on the Employee object (all fields are filled in), so it checks out there. But the Department object can have any number of ludicrous other constraints involved. Maybe IT only wants to hire a single person named Jenkins and it fails. Maybe IT has too many developers already and it fails. Maybe by adding a new employee, the Department object automatically totals up all salaries and sees that they're over the budget and fails. Maybe the Department hands off that salary total (which is not something the user typed in or even has any knowledge of!) to a parent Company object, which rejects it because even though the Department is still within what it was given as a salary constraint, the company as a whole would not be. And on and on and on. Is there a clever way to capture and report errors of this type back to the user? I considered stuffing all of the cascading salary logic into a validateSalary:error: method, for example, but then I'd do all the calculations for the related objects once when I validate, and then do them again when I actually set the Salary after all the checks succeed. If these operations are expensive, then I'd rather not do them multiple times. AFAIK, I'd have no good location to cache the calculated values created during the validate routine, short of just stuffing them into some global variable somewhere. I tried using validateForUpdate: on the individual objects, but that isn't invoked until the document is saved, which is potentially long after changes were made. I can manually call it against all updated objects in the context, I guess, though this is also a potentially wasteful operation. As a side note, I've never been able to successfully directly call this method and have an &error object available for me - they're always nulls, and hence I can't report anything back. I've also considered using a customValidateSalary method, called at the end of setSalary, which does validation on known related objects. But that breaks down if, for example, the Employee only knows to validate the Department object and never checks to see if the Company object tossed an error, because it wasn't even aware of it. To catch all modifications to all objects, I'm basically back to iterating over all updatedObjects again. Regardless, at the end of it all, after all the validations against all objects are performed, if any failed then I could undo the last action to restore to prior state and alert the user, but I lack the context of re-highlighting the field the way the standard validateSalary:error: CoreData methods would work. That's not as user friendly. I could also rewire all the setters to toss exceptions if an invalid input falls into them, wrap everything in try/catch blocks, and let them bubble up only to be captured at the highest level and finally displayed. I still lose context of which input field the user was typing into, though. Maybe capture the first responder and re-use that? I dunno. Does anyone have any suggestions about how to deal with cascading validation in this manner? It feels like I've got the OO equivalent of a stack of GOTO blocks to unwind this mess. Any suggestions welcome. -Jim.... _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
