Design issue for MVC and database updates

[sstevenson at mac.com (Scott Stevenson)]

On Mar 2, 2004, at 3:03 PM, Joakim Danielson wrote:

> Well the problem is not in the database methods really but more what I  
> must implement to see which object's how has changed. But I supply   
> the method anyway:
>
> - (IBAction)saveToDb:(id)sender

Your best bet is probably key-value observing (Panther only):
http://developer.apple.com/documentation/Cocoa/Conceptual/ 
KeyValueObserving/

You can observe each item, and whenever the a value changes in the  
object, you can add them item to a "changedObjects" mutable array. This  
is probably best done outside of the NSArrayController.


Then, you change your database saving action method to this:

- (IBAction)saveToDb:(id)sender {

     NSEnumerator *iterator;
     JDTransactionType *item;
     int newId;

     // get the list of changed objects
     NSMutableArray * changedObjects = [self changedObjects];
     iterator = [changedObjects objectEnumerator];

     ....

     // after you're done, empty the array
     [objectsToUpdate removeAllObjects];
}


I haven't yet found a way to ask NSArrayController which object it just  
edited (although it seems like a something a lot of people would use).  
But if someone else has, that would negate the need to observe each  
object separately.

I guess it would be pretty easy to override -objectDidBeginEditing to  
check -selection and add it to an array, or something of that nature.  
Not sure if it's reasonable to assume the selection is the one being  
edited.

     - Scott

--
Tree House Ideas
http://treehouseideas.com/