NSPredicate to test for NULL, and blank strings

Question

I have an NSArray and need to filter out any strings that are null or rather, have ' ' (empty string). How do I do that? I have tried doing:

NSPredicate *predicateName = [NSPredicate predicateWithFormat:@"(name!=nil)"];

but that doesn't seem to work. Or maybe it does but there are different kinds of null...

score 153 · Accepted Answer · edited Jun 23 '17 at 08:51

153

If you don't use Core Data, you could do:

NSPredicate *predicateName = [NSPredicate predicateWithFormat:@"name.length > 0"];

If the string is empty, this will fail (because 0 == 0). Similarly, if name is nil, it will also fail, because [nil length] == 0.

edited Jun 23 '17 at 08:51

Tamás Sengel

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answered Sep 10 '11 at 04:15

Dave DeLong

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So then what is the solution mate? This one actually seems to work for me where as the first answer doesn't. If string is empty, then wont length = 0? it isn't null – Doz Sep 10 '11 at 04:56
@Doron the solution is to use the predicate I suggested. – Dave DeLong Sep 11 '11 at 03:53
Sorry mate but i still get (null) in certain fields. So not sure what you meant by your comment after the code. == 0 so you are saying you are getting a value of 0, so all i need to test is > 0. to be 1. Because i am still getting (null) – Doz Sep 11 '11 at 11:24
2011-09-11 21:24:14.282 iKosher[89194:13703] Brand**COLES 2011-09-11 21:24:14.282 iKosher[89194:13703] Brand**WAITROSE 2011-09-11 21:24:14.283 iKosher[89194:13703] Brand**(null) 2011-09-11 21:24:14.283 iKosher[89194:13703] Brand**(null) 2011-09-11 21:24:14.283 iKosher[89194:13703] Brand**VILLAGE GREEN – Doz Sep 11 '11 at 11:24
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!!! **Beware with CoreData** length is not supported, and worse will fail silently returning strange results. CoreData translates the predicate `name.length > 1` to sqlite in `name > 1`... While it should be `length(name) > 1` – Vincent Guerci May 07 '12 at 14:06
@VincentG interesting. sounds like a bug. have you filed one? https://bugreport.apple.com – Dave DeLong May 07 '12 at 15:44
@Dave DeLong, just did, searched a while in `CoreData`/`NSPredicate` documentation, no mention at all of `length`. Makes sense that it works on object arrays thanks to `keypath` evaluation. But on sqlite, I presume that is not so obvious... Maybe a missing feature, but anyway, that should raise an error in that case. – Vincent Guerci May 07 '12 at 16:09
So does this answer not work then? I'm having a similar problem – trapper Oct 23 '12 at 14:17
I just used the suggested technique (i.e. name.length > 0) in a core-data NSPredicate and it worked as expected so if it was broken then it is fixed now (iOS 6.1 on Simulator). – Christopher King Feb 10 '13 at 19:12
I noticed that when `name`.length > 0 but `name` the first character is a whitespace -> it will not return it – Tal Bereznitskey Feb 18 '13 at 09:59
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Got tricked once again today by this one with CoreData... damn it. Kinda funny that I found my own previous comment looking for this :) – Vincent Guerci Mar 14 '13 at 12:38
@VincentG how about [using a regular expression](http://stackoverflow.com/a/14148659/375300) for a Core Data predicate (as long as it is performant enough)? – albertamg Aug 21 '13 at 13:24
what about objects that aren't strings? – Ben Collins Jan 27 '14 at 17:12
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@VincentG - then what is the solution for CoreData? – RyanJM Mar 05 '14 at 21:44
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This is very dangerous. @VincentG is right. I have a string with a leading '/' character which did not work with `.length`. I had to use the `name!=nil AND name!=''` like @josema.vitaminew posted – Stefan Arn Nov 20 '15 at 13:09

score 89 · Answer 2 · answered Jan 21 '13 at 14:47

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I think this should work:

NSPredicate *predicateName = [NSPredicate predicateWithFormat:@"name!=nil AND name!=''"];

answered Jan 21 '13 at 14:47

José Manuel Sánchez

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This works find for Realm database predicates as well. Thank you. – edhnb May 01 '17 at 15:41

score 14 · Answer 3 · answered Dec 20 '13 at 10:29

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 NSPredicate *predicateName = [NSPredicate predicateWithFormat:@"name!=NULL"];

answered Dec 20 '13 at 10:29

chroww

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score 7 · Answer 4 · answered Nov 18 '13 at 11:10

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This predicate worked for me:

[NSPredicate predicateWithFormat:@"(%K== nil) OR %K.length == 0", @"imageUrl", @"imageUrl"]

answered Nov 18 '13 at 11:10

Josip B.

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NSPredicate to test for NULL, and blank strings

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