Core Data NSPredicate for relationships

Question

My object graph is simple.

I've a feedentry object that stores info about RSS feeds and a relationship called Tag that links to "TagValues" object. Both the relation (to and inverse) are to-many. i.e, a feed can have multiple tags and a tag can be associated to multiple feeds.

I referred to How to do Core Data queries through a relationship? and created a NSFetchRequest. But when fetch data, I get an exception stating,

NSInvalidArgumentException unimplemented SQL generation for predicate

What should I do? I'm a newbie to core data :( I know I've done something terribly wrong... Please help...

Thanks

--

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
// Edit the entity name as appropriate.
NSEntityDescription *entity = [NSEntityDescription entityForName:@"FeedEntry" inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];
// Edit the sort key as appropriate.
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"authorname" ascending:NO];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];

[fetchRequest setSortDescriptors:sortDescriptors];

NSEntityDescription *tagEntity = [NSEntityDescription entityForName:@"TagValues" inManagedObjectContext:self.managedObjectContext];
NSPredicate *tagPredicate = [NSPredicate predicateWithFormat:@"tagName LIKE[c] 'nyt'"];          
NSFetchRequest *tagRequest = [[NSFetchRequest alloc] init];
[tagRequest setEntity:tagEntity];
[tagRequest setPredicate:tagPredicate];

NSError *error = nil;
NSArray* predicates = [self.managedObjectContext executeFetchRequest:tagRequest error:&error];


TagValues *tv = (TagValues*) [predicates objectAtIndex:0];
NSLog(tv.tagName); // it is nyt here...


NSPredicate *predicate = [NSPredicate predicateWithFormat:@"tag IN %@", predicates];
[fetchRequest setPredicate:predicate];


// Edit the section name key path and cache name if appropriate.
// nil for section name key path means "no sections".
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"];
aFetchedResultsController.delegate = self;
self.fetchedResultsController = aFetchedResultsController; 

--

Solution 1

The key here is "ANY"

Example from apple:

NSPredicate *predicate = [NSPredicate predicateWithFormat:
    @"ANY employees.firstName like 'Matthew'"];

http://developer.apple.com/mac/library/documentation/cocoa/conceptual/CoreData/Articles/cdBindings.html

Solution 2

Do you require SQLite? I am grappling with a similar issue, and have found that everything works as expected with a binary store.
There are limitations when using SQLite as a store, though I have not yet found a document that lists the limitations, only that they exist.

Sorry I can't be of more help.

Comments

[catsby]

post some of your code so we can have a better look

[Barry Wark]

Mungunth, it looks like you may be forgetting to set the entity of the fetchRequest after re-setting the predicate to 'tag IN predicates'. If this isn't the issue, please also post a pic of the object model and I can give you a bit more guidance.

[Mugunth]

I got the answer through devforums.apple.com. Till the NDA is in place, I can't divulge the answer... :(

[Mugunth]

Yes, it works with a binary store. I used a sql lite db as it seems to be faster in my case. I deal with data of sizes close to 5MB (on iPhone). App loading time is < 1sec for sqlite where as it's close to 2 sec for binary store.

[Mugunth]

I foudn the answer though... NSPredicate *predicate = [NSPredicate predicateWithFormat:@"tag IN %@", predicates]; [fetchRequest setPredicate:predicate]; should be changed to NSPredicate *predicate = [NSPredicate predicateWithFormat:@"ANY tag IN %@", predicates]; [fetchRequest setPredicate:predicate];

[emp]

Good to know - it's strange, your message is very similar to one I had, and yet mine is due to a limitation of Core Data with SQLite. Know to figure out how to tell the difference!