Question

I am writing an application using Core Data which heavily depends on setting attributes from string values. However, I am running into a problem because Core Data, when it creates wrapper methods, uses NSNumber to represent all of the numeric fields. Therefore, if I pass in a String using key/value coding setValue:forKey: it gives me a type error:

For instance, I have an object type “Building”. In the datamodel, I have an attribute called “fbFloors” set to integer 32.

Then, in my code, I do the following:

Building * b = [NSEntityDescription insertNewObjectForEntityForName:@”Building” inManagedObjectContext:ctx];
[b setValue:@”2″ forKey:@”fbFloors”];

This raises the following exception:

Terminating app due to uncaught exception ‘NSInvalidArgumentException’, reason: ‘Unacceptable type of value for attribute: property = “fbFloors”; desired type = NSNumber; given type = __NSCFConstantString; value = 2.’

I would like it to coerce the string value to a number, but it doesn’t want to. I tried implementing coerceValueForFbFloors: but it looks like that is only available in Mac OS X, not iOS.

Any ideas?

Answer 1

You have to pass an actual instance of NSNumber to setValue. Something like:

[b setValue[NSNumber numberWithInt:2] forKey:@”fbFloors”];

If your data is appearing as a string, then you can use NSNumberFormatter to convert it first to an NSNumber.