Question

Given and coredata based app using an Indexcard metaphor. Each Indexcard can optionally have a one-to-many relationship with a number of other entities/tables; i.e. I’ll use Momento’s ‘Moment’ as a proxy for my Indexcard object and Momento’s ancillaries of tags, locations, etc. , for these other objects/tables.

What is the ‘fastest’ way to show whether or not these foreign table relationships exist on probably the most important tableView in the entire app?

and

What would be the best approach for laying out the cell portion showing whether or not a relationship exists and the count of the number of each type of relationship?

Again, using Momento as a design pattern. With a link to a screenshot on Flickr (because stackOverflow won’t let me post an image since I’m a noob.)

Maybe my ex-RDBMS stuff is contaminating my thinking, but they didn’t do a mongo-join to get the values off to the right did they? [tags,events,people,locations]. There has to be a more elegant way that I’m just not seeing.

My thoughts for laying out the cells on the right was to possibly use some boolean if YES put up the icon and the count, but that seems pretty expensive for every cell.

I’m sure that the answer to this layout question would be driven by the approach taken in the first part of the problem. It doesn’t seem that I would want to store ancillary relationships in the ‘main/moment’ IndexCard object for maintenance reasons.

Thanks in advance for any help.

Answer 1

If you set up a one-many relationship of indexcards to tags(or whatever), a fetched indexcard object should have an NSSet of tags as a property. Same for the others, and you should just be able to get the count of the set and display that next to each of the appropriate icons.

..Unless I’m misunderstanding your question.

edit: to answer the second part, you should indeed have a conditional in cellForRowAtIndex path that checks the count of each set and either just display it with the icon (possible to have 0 then, which is normally fine), or check whether it is 0 and hide the image if it is as you said. I don’t think either solution will slow down your app since the data has already been fetched anyway by the time the cell is being rendered, but the solution where you just pass the count right through without checking if it’s 0 would generally be fast overall.

edit to provide some sample code:
Your Core Data model would have an IndexCard entity and then an entity for each type of possible related object.

1)Model:

IndexCard – has a one-many relationship with each of the other entities

Tag

Location

Person

2)After creating this model and the corresponding Object classes you will end up with an IndexCard class that has the following in its header

@property (nonatomic, strong) NSSet *tags
@property (nonatomic, strong) NSSet *locations
@property (nonatomic, strong) NSSet *people

and of course the following in its implementation

@dynamic tags
@dynamic locations
@dynamic people

3)Now that we’ve established this Core Data model, we can perform an nsfetchrequest (of course when using a tableview, you should use an nsfetchedresultscontroller as it will dynamically fetch the IndexCards it needs as you’re scrolling through the table). This code assumes that we have a usable NSManagedObjectContext in its scope (ideally passed in from the AppDelegate and set as an ivar) and that our IndexCard object has some sort of key/id property we can search by, lets call it “number”

NSNumber *numberWeWant = [NSNumber numberWithInt:1];

NSFetchRequest *request = [[NSFetchRequest alloc] init];
request.entity = [NSEntityDescription entityForName:@"IndexCard" inManagedObjectContext:ourContext];
request.predicate = [NSPredicate predicateWithFormat:@"number == %@", numberWeWant];

NSError *error = nil;

NSArray *results = [context executeFetchRequest:request error:&error];

//didn't bother error checking in case no IndexCard matches
IndexCard *ourCard = [results lastObject];

//you can now use these to display in the cell or hide the appropriate icons if they = 0
int numTags = ourCard.tags.count;
int numLocations = ourCard.locations.count;
int numPeople = ourCard.people.count;

//just a sample of how we would access the individual related objects
for(Tag *tag in ourCard.tags)
{
    //do whatever you want with each tag here
}

Again, this code is just to fetch a single IndexCard. In an actual table you would be initializing an nsfetchedresultscontroller when loading the view that contains it, and then just accessing the IndexCard at the position matching IndexPath.row in cellForRowAtIndexPath.

This also assumes there are a finite number of types of objects that IndexCard can be related to. If the types can change and increase randomly, this approach would need to be modified.

Hopefully this helps.