Setting up a CoreData regular expression predicate for a comma-separated list

问题

I'm beating my head against a wall trying to get a regular expression function to work with a CoreData fetch. I have an attribute named maps on an NSManagedObject subclass that I'm trying to filter by. This maps attribute is a string with a list of id values like so:

1,10,12,8

Here's how my predicate is being constructed:

NSString *format = [NSString stringWithFormat: @"(maps matches '.*\\b%@\\b.*')", _map.mapID];
NSPredicate *predicate = [NSPredicate predicateWithFormat:format];
[request setPredicate:predicate];

NSManagedObjectContext *moc = [[RKManagedObjectStore defaultObjectStore] primaryManagedObjectContext];
_resultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request
                                                         managedObjectContext:moc
                                                           sectionNameKeyPath:@"name.stringGroupByFirstInitial"
                                                                    cacheName:nil];

I built the RegEx using this Rubular example: http://rubular.com/r/zELaz19x0T

The mapID value is an integer as a string.

I've read the other questions on SO about the predicate matching against the entire string, but I feel like that should be handled with this pattern using the .* at the beginning and end of the pattern.

The result of this code always returns zero results. If the predicate is not used, all objects are returned as expected. Can anyone see what the issue is here? Thanks!

回答1:

This is solved with this code:

NSString *format = @"(maps MATCHES %@) OR (maps == '')";
NSString *pattern = [NSString stringWithFormat:@".*(\\b%@\\b).*", _map.mapID];
NSPredicate *predicate = [NSPredicate predicateWithFormat:format, pattern];

I was assuming the format of the predicate was the same as formatting a string, which is not. I was enlightened by this other answer: https://stackoverflow.com/a/12672462/189292

来源：https://stackoverflow.com/questions/17180308/setting-up-a-coredata-regular-expression-predicate-for-a-comma-separated-list

标签

objective-c

regex

core-data

nspredicate