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POWord boundaries (\b) in NSPredicate causing NSFetchRequest to return no managed objects
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copied!<p>Using Core Data w/a sqlite store on iPhone.... I've got a bunch of comic book image entities, each with a string that includes the comic's issue#, e.g.: <code>image.imageTitle = @"Issue 12: Special Edition";</code></p> <p>Part of the UI allows the user to type in an issue number to jump to the next issue. My initial code for this was sloooooooow because <code>imageAtIndex:</code> queries Core Data for one object at a time. Over several hundred issues, it could take upwards of 40 seconds just to get through the first loop!</p> <p><em>Slow Code:</em></p> <pre><code> // Seek forward from the next page to the right for (i = currentPage + 1; i < [self numberOfPages]; i++) { iterationString = [[self imageAtIndex:i] imageTitle]; iterationNumber = [[iterationString stringByTrimmingCharactersInSet:nonDigits] intValue]; if (issueNumber == iterationNumber) { keepLooking = NO; break; } } // If nothing was found to the right, seek forward from 0 to the current page if (i == [self numberOfPages] && keepLooking) { for (i = 0 ; i < currentPage; i++) { iterationString = [[self imageAtIndex:i] imageTitle]; iterationNumber = [[iterationString stringByTrimmingCharactersInSet:nonDigits] intValue]; if (issueNumber == iterationNumber) { keepLooking = NO; break; } } } </code></pre> <p>Hoping for a much more efficient solution, I decided to try making a direct query on Core Data like so:</p> <pre><code> NSString *issueNumber = @"12"; NSString *issueWithWordBoundaries = [NSString stringWithFormat:@"\\b%@\\b",issueNumber]; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(groupID == %@) AND (imageTitle CONTAINS %@)", groupID, issueWithWordBoundaries]; NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"CBImage" inManagedObjectContext:self.managedObjectContext]; [fetchRequest setEntity:entity]; [fetchRequest setPredicate:predicate]; [fetchRequest setIncludesSubentities:NO]; // Not sure if this is needed, but just in case.... // Execute the fetch NSError *error = nil; NSArray *fetchedObjects = [managedObjectContext executeFetchRequest:fetchRequest error:&error]; // [fetchedImages count] == 0 </code></pre> <p>Between the <a href="http://developer.apple.com/mac/library/documentation/cocoa/conceptual/Predicates/Articles/pSyntax.html#//apple_ref/doc/uid/TP40001795-SW1" rel="nofollow noreferrer">Predicate Programming Guide</a> and the <a href="http://userguide.icu-project.org/strings/regexp" rel="nofollow noreferrer">ICU regex specs</a>, I figured the \b's would help prevent a search for 12 returning 120, 121, 122, etc. Instead, it doesn't return anything from the store at all!</p> <p>On the other hand, if I leave off the word boundaries and search instead for <code>stringWithFormat:@"%@",issueNumber</code>, I get dozens of managed objects returned, from 12 to 129 to 412.</p> <p>My best guess at this point is that I've run into one of Core Data's <a href="http://developer.apple.com/mac/library/documentation/cocoa/conceptual/Predicates/Articles/pBasics.html#//apple_ref/doc/uid/TP40001792-249799" rel="nofollow noreferrer">Constraints and Limitations</a>. If not, what am I doing wrong? If so, is there a workaround that offers both an exact match <em>and</em> the speed of a single fetch?</p>

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