Core data parent child relationship - core-data

Question

I have a basic question regarding Core Data.
I have 2 tables one to many.
I have setup the app to add children to the parent, but I cannot understand how I set the relationship so that when I add a new child via a view controller that It adds the child to the correct parent.
I have generated the entity subclasses and have managed to get the app to add a child (but it adds it to index 0), but I cant seem to work a fetchrequest that finds the correct parent.
- (IBAction)save:(id)sender {
NSManagedObjectContext *context = [self managedObjectContext];
Child *newChild = [NSEntityDescription insertNewObjectForEntityForName:#"Child" inManagedObjectContext:context];
[newChild setValue:self.childName.text forKey:#"childName"];
[newChild setValue:self.born.text forKey:#"born"];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"ParentList" inManagedObjectContext:context];
[fetchRequest setEntity:entity];
NSError *error = nil;
NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
ParentList *parent = [fetchedObjects objectAtIndex:0]; //this adds it to the first parentList in list at index 0 not to the correct parent
NSLog(#"parent: %# created", league);
[parent addChildObject: newChild];
//
///////////////////////////////////////////
//////index path is wrong//////////////////
///////////////////////////////////////////
}
NSError *error = nil;
// Save the object to persistent store
if (![context save:&error]) {
NSLog(#"Can't Save! %# %#", error, [error localizedDescription]);
}
[self dismissViewControllerAnimated:YES completion:nil];
}

Answer 1

You need to pass the parent's objectID to the second view controller (if I understood your setup correctly).
Fetch the parent (using existingObjectWithID:error: of the NSManagedObjectContext) in the other view context.
Set the child parent as the fetched object.
should look something like:
NSError* error = nil;
NSManagedObjectID* parentID = //the parent object id you selected
Parent* parent = [context existingObjectWithID:parentID error:&error];
if (parent) { //parent exists
Child *newChild = [NSEntityDescription insertNewObjectForEntityForName:#"Child"
inManagedObjectContext:context];
[newChild setValue:self.childName.text forKey:#"childName"];
[newChild setValue:self.born.text forKey:#"born"];
[newChild setValue:parent forKey:#"parent"];//Set the parent
} else {
NSLog(#"ERROR:: error fetching parent: %#",error);
}
Edit:
To get the selected object id (assuming you are using a NSFetchedReaultsController):
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
NSManagedObject *object = [[self fetchedResultsController] objectAtIndexPath:indexPath];
//Use object.objectID as the selected object id to pass to the other view controller
//what ever you need to do with the object
}