title: Cocoa Core Data: Setting default entity property values?
body: <p>I know I can set default values either in the datamodel, or in the -awakeFromInsert method of the entity class. For example, to make a "date" property default to the current date:</p>
  
  <pre><code>- (void) awakeFromInsert
  {
  NSDate *now = [NSDate date];
  self.date = now;
  }
  </code></pre>
  
  <p>How though can I make an "idNumber" property default to one greater than the previous object's idNumber?</p>
  
  <p>Thanks, Oli </p>
  
  <p><strong>EDIT: Relevant code for my attempt (now corrected)</strong></p>
  
  <pre><code>- (void) awakeFromInsert
  {
  self.idNumber = [NSNumber numberWithInt:[self maxIdNumber] + 1];
  }
  
  -(int)maxIdNumber{
  NSManagedObjectContext *moc = [self managedObjectContext];
  NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Flight" inManagedObjectContext:moc];
  NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
  [request setEntity:entityDescription];
  
  // Set example predicate and sort orderings...
  NSPredicate *predicate = [NSPredicate predicateWithFormat:@"idNumber &gt; %@", [NSNumber numberWithInt:0]];
  [request setPredicate:predicate];
  
  [request setFetchLimit:1];
  
  NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"idNumber" ascending:NO];
  [request setSortDescriptors:[NSArray arrayWithObject:sortDescriptor]];
  [sortDescriptor release];
  
  NSError *error;
  NSArray *array = [moc executeFetchRequest:request error:&amp;error];
  if (array == nil | array.count == 0)
  {
      return 0;
  } 
  return [[[array objectAtIndex:0] valueForKey:@"idNumber"] intValue];
  }
  </code></pre>
  
  <p>If the maxIdNumber method is called, the new object is added to the table twice!? (but with the correct idNumber). The two entries in the table are linked - editing / removing one also edits / removes the other. For this reason I believe it has something to do with the managed object context. For what its worth, the outcome (two copies) is the same no matter how many times the maxIdNumber method is called in the awakFromNib; even if self.idNumber is just set to [NSNumber numberWithInt:5] and the maxIdNumber method is just called for a throwaway variable. </p>
  
  <p>Any clues??</p>