对核心数据中的实体之间的属性执行计算

Question

I am new to xcode/ios etc... and having a little trouble figuring out a problem. I cant seem to figure out how I would retrieve and perform calculations on attributes between entities in core data. Here is an example of what I am trying to do:

My project is a football app that has a one to many relationship. Season to Game (Season has a bunch of games. Season has attributes like teamname and datestart. Game has attributes like passing yards, running yards etc..

How would I be able to calculate something like total passing yards for the whole season (adding all the games passing yards together for that season)?

Thanks for your time.

Answer 1

You managed object for Season has a relationship named hasGames (or whatever you named the relationship to the games). When you have a Season managed object, you can just access the hasGames relationship (it's an NSSet ), loop through all the games in there and do whatever you want with the data, eg adding some values up.

EDIT :

Example:

If I take your Relationships Career -> Season -> Game, and suppose the relationships are called Career.hasSeasons and Season.hasGames, it would look something like this

int passingYards = 0;

Career* myCareer = [... fetchedresult for the career you are looking for ...];

for(Season* season in myCareer.hasSeasons)
{
  for(Game* game in season.hasGames)
  {
    careerPassingYards += [game.passingYards intValue];
  }
}

Answer 2

I ended up finding this code here on stack. After properly setting up my fetchedResultsController I am able to use this code in a button or where ever needed to calculate the total passing yards for all of the games in my season.

int totalpassingyards = 0;
for (NSManagedObject *object in [self.fetchedResultsController fetchedObjects]) {
    NSNumber *objectTotalPassingYardsNumber = [object valueForKey:@"passingyards"];
    int objectTotalPassingYards = [objectTotalPassingYardsNumber intValue];      
    totalpassingyards = totalpassingyards + objectTotalPassingYards;
}
NSLog(@"Subtotal: %i", totalpassingyards);

My next step is to figure out how to calculate the total passing yards for all of the seasons in my career list. Here is how my coredata relationships are set up.

Career          >       Season      >       Game
(career stats)          (season stats)      (game stats)

career stats = sum of season stats
season stats = sum of game stats
game stats = that individual games stats

I am guessing this will consist of creating two fetchedResultsControllers one holding the games and one for holding the seasons and then doing some type of nested loop to get through all them. I will keep everyone updated.

If anyone has a better way to do this let me know like I said I am very new to this so everything really comes down to trail and error and although it might work I understand it might not be the best way to do it lol.