Validating data and looping through NSSet

Question

I have a CoreData (SQLite) datamodel in xcode like so:

Friends Table
  email
  name
  username
  belongsToGroups

Groups Table
  title
  peopleInGroup

So the belongsToGroups and peopleInGroups is a many-to-many relationship with each other, both represented by NSSet in the code.

What do I use to query the NSSet for people in my groups and vice versa? (I'm new to CoreData)

Answer 1

With coredata, you can do it simple. Assume we have one object on Groups Table ( group), you want to get all friends belong to group, you can do:

[group. peopleInGroup allObjects]

For more detail:

1. Get group via title

NSError* error = nil;
NSFetchRequest* fetchRequest = [[NSFetchRequest alloc] init];
NSPredicate *predicate;
NSEntityDescription *entity;
NSArray *fetchedObjects;    
Group* group;    
entity = [NSEntityDescription
          entityForName:[NSString stringWithFormat:@"%@",[Group class]]
          inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
predicate = [NSPredicate predicateWithFormat:[NSString stringWithFormat:@"(title like[c] \"%@\")" ,title]];
[fetchRequest setPredicate:predicate];
fetchedObjects = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
if (fetchedObjects.count > 0) {
    group = [fetchedObjects lastObject];
}
return group;

}

1. Get all friend of group

   NSMutableArray* friends = [NSMutableArray alloc] init]; [friends addObjectsFromArray:[group. peopleInGroup allObjects]];