[Rubycocoa-talk] Core Data and Dependent Keys

[Knud H. M. <knu...@de...>]

Hi all,

I'm trying to implement something with dependent keys in core data. I  
try to follow the documentation at:

http://developer.apple.com/documentation/Cocoa/Conceptual/KeyValueObserving/Concepts/DependentKeys.html

Basically, I implement a subclass of NSManagedObject which includes a  
custom method "fullName" for the dependent key (fullname depends of  
"firstName" and "lastName"). To make it work, I need to call  
setKeys:triggerChangeNotificationsForDependentKey: on my subclass. I  
implemented this in ObjC, and it works just fine:

@implementation DKTEntity

+ (void)initialize {
     [self setKeys: [NSArray arrayWithObjects: @"firstName",  
@"lastName", nil]
		triggerChangeNotificationsForDependentKey:@"fullName"];
}

- (NSString *)fullName {
     return [NSString stringWithFormat: @"%@ %@",
			[self firstName],
			[self lastName]];
}
@end

Now I tried to do the same in RubyCocoa, like this:

class DKTEntity < OSX::NSManagedObject

   def DKTEntity.initialize
      
DKTEntity 
.setKeys_triggerChangeNotificationsForDependentKey(["firstName",  
"lastName"], "fullName")
   end

   def fullName
     # this is the definition of the dependent key fullName
     return "#{firstName} #{lastName}"
   end

end

However, this results in an ugly crash upon startup:

2008-02-27 17:35:41.473 DependentKeysTest[1178:10b]  
AppDelegate#rbValueForKey: RuntimeError: Ruby object  
`OSX::DKTEntity_DKTEntity_' doesn't respond to the ObjC selector  
`initialize', the method either doesn't exist or is private

I'm new to RubyCocoa (and Ruby) and have no real clue as to what the  
problem is here? Is it the way I override the initialize class method?  
I tried other idioms, but the error remains the same. I also tried to  
call setKeys... outside any initialize method, like so:

class DKTEntity < OSX::NSManagedObject

      
DKTEntity 
.setKeys_triggerChangeNotificationsForDependentKey(["firstName",  
"lastName"], "fullName")

     ...
end

This doesn't crash, but unfortunately doesn't seem to have any effect  
at all (fullName will remain unspecified).

If you want to play around with the code, look here:

ObjC version: http://sw.deri.org/~knud/stuff/DependentKeyTestObjC.zip
Ruby version: http://sw.deri.org/~knud/stuff/DependentKeysTest.zip

Any help appreciated!

Cheers,
Knud
-------------------------------------------------
Knud Möller, MA
+353 - 91 - 495086
Smile Group: http://smile.deri.ie
Digital Enterprise Research Institute
   National University of Ireland, Galway
Institiúid Taighde na Fiontraíochta Digití
   Ollscoil na hÉireann, Gaillimh