Advanced Core Data Model Help

[Whitehk]

I'm making a school planner app and I'm having a heck of a time with core data. I have an EXTREMELY advanced data model. Here is what I've got so far:



As you can see, I wasn't kidding about the level of simplicity. Let me explain it.

A course is the main relational entity here; however, none of the attributes or relationships are required. There can be multiple courses. Each course can optionally contain a name and location. Each course can also optionally contain multiple classDay and teacher entities (many-to-many relationship) and one period entity (many-to-one relationship).

And of course, all of these can be inverted: While a course can be on multiple class days, a class day can be associated with multiple courses. While a course can have multiple teachers, a teacher can teach multiple courses. And finally, While a course can be during one period, a period can be associated with one course. Also, a period can be during one PeriodTime.

A course can also have multiple assignments; however, an assignment can only be for one course. An assignment can also be of multiple types and vise versa.

When you delete a course, all of the assignments associated with it are deleted as well. When you delete a period, the period's time is deleted as well. And when you delete an assignment type, all the assignments associated with that type are deleted as well.

-------------------------------

Like I said, VERY complex. I guess my question is: how would I deal with so many different relationships like this? Would I need multiple managedObjectContexts for each different relationship? Sorry for the long question. I've been working at this for about a week and a half now and it's driving me crazy!

[BrianSlick]

It's not THAT complicated. They didn't write the framework just to deal with one or two entities.

And your question is too vague. What are you having trouble doing?

[Whitehk]

Originally Posted by BrianSlick

It's not THAT complicated. They didn't write the framework just to deal with one or two entities.

And your question is too vague. What are you having trouble doing?

Well, specifically, It crashes and I get

"Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'to-many key not allowed here'"

whenever I try to create my fetchedResultsController in the console. Like I said in the previous post, how would I go about handling these different relationships? To me this sounds like you have to make certain modifications for a to-one relationship and different modifications for a to-many relationship. Would I be correct in saying this?

Here's the code to create the controller:

- (NSFetchedResultsController *)fetchedResultsController {
    
    if (fetchedResultsController != nil) {
        return fetchedResultsController;
    }
    
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Course" inManagedObjectContext:managedObjectContext];
    [fetchRequest setEntity:entity];
    
    NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:@"classDay.dayName" ascending:NO];
    [fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]];
    
    [fetchRequest setFetchBatchSize:20];
    
    NSFetchedResultsController *theFetchedResultsController = 
    [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"];
    self.fetchedResultsController = theFetchedResultsController;
    fetchedResultsController.delegate = self;
    
    [sort release];
    [fetchRequest release];
    [theFetchedResultsController release];
    
    return fetchedResultsController;    
    
}

Here's my viewDidLoad where I get the crash:

- (void)viewDidLoad {
    [super viewDidLoad];

    NSError *error;
	if (![[self fetchedResultsController] performFetch:&error]) { /*this is the offending line*/
		// Update to handle the error appropriately.
		NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
		exit(-1);  // Fail
	}
    
}

[BrianSlick]

core data to many sorting on fetch - Stack Overflow

[Whitehk]

Originally Posted by BrianSlick

core data to many sorting on fetch - Stack Overflow

Thanks for the reference. I'll take a look at it and see what I can do.

[Whitehk]

Originally Posted by BrianSlick

core data to many sorting on fetch - Stack Overflow

Alright. So I looked over it, and I'm still not understanding something important. Why is a to-many key not allowed in my fetchedResultsController method? It seems to be something wrong with the sort descriptors because whenever I change

NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:@"classDay.dayName" ascending:YES];

to sort by the course name rather than the classDay name with this:

NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];

It doesn't crash. How come I can't sort by the classDay.dayName key?

[BrianSlick]

Did you try the solution as described in the link?

[Whitehk]

Originally Posted by BrianSlick

Did you try the solution as described in the link?

Yes. I got the same results. However in the example you gave me, wouldn't the Person entity be akin to my ClassDay entity and the Event entity to my Course entity? If that's the case, they seem to be fetching the ClassDay Entity. I want to fetch the Course entity. I'm looking more for what the user Wienke said:

If I understand correctly, you want to fetch "event" (course) entities and sort them according to their eventTitle (course name) attribute. So you would set up your sort descriptors for those entities the same as you would for your to-one fetches, since eventTitle (course name) is a to-one attribute. You'd then access the "person" (ClassDay) entities through the retrieved "event" (course) entities. – Wienke

Here's what I came up with in my code:

NSSortDescriptor *classDaySortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"classDay.dayName" ascending:YES];
    NSSortDescriptor *courseSortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:classDaySortDescriptor, courseSortDescriptor, nil];
    
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Course" inManagedObjectContext:managedObjectContext];
    [fetchRequest setEntity:entity];
    [fetchRequest setSortDescriptors:sortDescriptors];
    [fetchRequest setFetchBatchSize:20];
    
    NSFetchedResultsController *theFetchedResultsController = 
    [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"];
    self.fetchedResultsController = theFetchedResultsController;
    fetchedResultsController.delegate = self;
    
    [classDaySortDescriptor release];
    [courseSortDescriptor release];
    [sortDescriptors release];
    [fetchRequest release];
    [theFetchedResultsController release];