NSManagedObject with Rails-ish timestamps

NSManagedObjectWithTimestamps.h

//
//  NSManagedObjectWithTimestamps.h
//  Brainbow Apps, 2011
//

#import <Foundation/Foundation.h>

@interface NSManagedObjectWithTimestamps : NSManagedObject {
  NSDate *createdAt;
  NSDate *modifiedAt;
}

@property (assign) NSDate *createdAt;
@property (assign) NSDate *modifiedAt;

@end

NSManagedObjectWithTimestamps.m

//
//  NSManagedObjectWithTimestamps.m
//  Brainbow Apps, 2011
//

#import "NSManagedObjectWithTimestamps.h"

@implementation NSManagedObjectWithTimestamps

@dynamic modifiedAt, createdAt;

- (void)willSave {
  [self setPrimitiveValue:[NSDate date] forKey:@"modifiedAt"];
  if (![self primitiveValueForKey:@"createdAt"]) 
    [self setPrimitiveValue:[NSDate date] forKey:@"createdAt"];
  [super willSave];
}

@end