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POHow do I set up an NSPredicate that filters for items in a specified group using NSFetchedResultsController
 

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  1. POHow do I set up an NSPredicate that filters for items in a specified group using NSFetchedResultsController
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    <p>I have a Group entity which has many Item entities. An Item entity can be in multiple groups. The relevant portion of my model looks like this:</p> <p><img src="https://dl.dropbox.com/u/2523010/CoreDataQuestion.png" alt="alt text"></p> <p><strong>The Problem</strong></p> <p>When I call</p> <pre><code>[fetchedResultsController performFetch:&amp;error] </code></pre> <p>I get this error in the console</p> <pre><code>*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'to-many key not allowed here' *** </code></pre> <p>I'm pretty sure the problem is in how I'm setting up the predicate here:</p> <pre><code>[NSPredicate predicateWithFormat:@"groups == %@", self.group]; </code></pre> <p>But I can't tell what I'm doing wrong. I've read over the NSPredicate documents and I've tried this:</p> <pre><code>[NSPredicate predicateWithFormat:@"ANY groups IN %@", [NSArray arrayWithObject:self.group]]; [NSPredicate predicateWithFormat:@"ANY groups LIKE %@", self.group]; [NSPredicate predicateWithFormat:@"ANY groups == %@", self.group]; [NSPredicate predicateWithFormat:@"ANY groups IN %@", [NSArray arrayWithObject:self.group]]; [NSPredicate predicateWithFormat:@"groups == %@", self.group]; </code></pre> <p>None of which work. This has got to be simple, but I can't figure it out. I simply want the predicate to filter all the items so as to only return items that are members (through the model relationship) of the group. How do you do this?</p> <p>I have a NSFetchedResultsController that I am trying to configure to show only the items in a specific group. My code to setup the NSFetchedResultsController looks like this:</p> <pre><code>// create the fetch request NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; // configure the entity NSEntityDescription *entity = [NSEntityDescription entityForName:@"Item" inManagedObjectContext:managedObjectContext]; [fetchRequest setEntity:entity]; // configure the predicate NSPredicate *predicate = [NSPredicate predicateWithFormat:@"groups == %@", self.group]; [fetchRequest setPredicate:predicate]; // configure the sort descriptors NSSortDescriptor *indexSortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"uniqueID" ascending:YES]; NSArray *sortDescriptors = [NSArray arrayWithObject:indexSortDescriptor]; [fetchRequest setSortDescriptors:sortDescriptors]; // create the fetched results controller NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:nil cacheName:@"ItemsCache"]; // configure the fetched results controller aFetchedResultsController.delegate = self; </code></pre>
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    1. COI used to handle many-to-many relationship by breaking the relationship by another entity. May be the following question shows how I did it. http://stackoverflow.com/questions/2822625/core-data-many-to-many-relationship-nspredicate You can also use the predicate editor from the data model editor to construct the predicate. I hope that helps you,
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      1. USSarah
    2. COThe reminder about the predicate editor was helpful. I still haven't figured it out yet, but thanks!
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      1. POHow do I set up an NSPredicate that filters for items in a specified group using NSFetchedResultsController
      1. USDavid Weiss
 

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