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;
--
Inverse relationships enable Core Data to propagate change in both directions when an instance of either the source or destination type changes. Every relationship must have an inverse. When creating relationships in the Graph editor, you add inverse relationships between entities in a single step.
Fetched Properties in Core Data are properties that return an array value from a predicate. A fetched property predicate is a Core Data query that evaluates to an array of results.
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
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.
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