Question

I am developing an application where i used core data framework for the purpose of maintaining a database. My entity contains three attributes called: name, start time and end time of a list of applications. I am getting the correct values for name and start time attribute.
Now my problem is my end time attribute should contain the value of the next entries start time value. If anybody having any idea about this please let me know.

Thanks

Answer 1

You can leave the endTime attribute blank until you create the next entity. In the +Create category on the entity, get the last/first object (assuming you are using ordered entities) and update the endTime with the same value used for the new startTime.

If your objects are not ordered it could be a bit tricky since all the entities are in a set. But if ordered, you are good since NSOrderedSet responds to lastObject (and firstObject).

Enjoy,

Damien

EDIT: Here is an example factory method that either 1) returns the existing stock entity for a stock symbol or 2) creates a new entity for that symbol. Pretty easily modified to get entities and select the first/last depending on your sort order. Again see the Core Data classes from Prof. Hegarty.

 + (Stock *)stockForSymbol:(NSString *)symbol inManagedObjectContext:(NSManagedObjectContext *)context {
  Stock *stock = nil;

  NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Stock"];
  request.predicate = [NSPredicate predicateWithFormat:@"symbol = %@",symbol];
  NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"symbol" ascending:YES];
  request.sortDescriptors = [NSArray arrayWithObject:sortDescriptor];

  NSError *error = nil;
  NSArray *matches = [context executeFetchRequest:request error:&error];

  if (!matches || [matches count] > 1) {
      // handle error
  } else if ([matches count] == 0) {
      stock = [NSEntityDescription insertNewObjectForEntityForName:@"Stock" inManagedObjectContext:context];
      stock.symbol = symbol;
      stock.strategyPosition = [NSNumber numberWithInt:StrategyPositionFlat];
      stock.userPosition = stock.strategyPosition;
      stock.userOwns = [NSNumber numberWithBool:NO];
  } else {
      stock = [matches lastObject];
  }
  return stock;
}