Core Data fetch request with array

Question

I am trying to set a fetch request with a predicate to obtain records in the store whose identifiers attribute match an array of identifiers specified in the predicate e.g.

NSString *predicateString = [NSString stringWithFormat:@"identifier IN %@", employeeIDsArray];

The employeeIDsArray contains a number of NSNumber objects that match IDs in the store. However, I get an error "Unable to parse the format string". This type of predicate works if it is used for filtering an array, but as mentioned, fails for a core data fetch. How should I set the predicate please?

Dulgan · Accepted Answer · 2014-12-16 09:39:44Z

11

NSPredicate doesn't use formats like NSString does. So that the result of a predicate creation using the pre-generated predicateString won't be a valid predicate.

You have to make it an actual predicate:

NSPredicate * predicate = [NSPredicate predicateWithFormat:@"identifier IN %@", employeeIDsArray];
[fetchRequest setPredicate:predicate];

See the documentation for more informations on predicate formats.

edited Dec 16, 2014 at 9:39

Dulgan

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answered Apr 15, 2010 at 17:33

Dave DeLong

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2 Comments

RunLoop Over a year ago

Thanks, but of course I do call: NSPredicate *predicate = [NSPredicate predicateWithFormat:predicateString];

RunLoop Over a year ago

Apologies for not accepting your answer earlier. I have tried your suggestion and it works.

Peter Hosey · Accepted Answer · 2010-04-15 19:42:16Z

4

When you create that string using stringWithFormat:, that method inserts the array's description (a string describing the contents of the array) where you had %@.

That's not what you want. You don't want to test membership in a string describing the array; you want to test membership in the array. So, don't go through stringWithFormat:—pass the format string and the array to predicateWithFormat: directly.

answered Apr 15, 2010 at 19:42

Peter Hosey

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2 Comments

RunLoop Over a year ago

Thank you. Had to give "Answered" to the first poster, but +1 because thanks to you I now understand why.

Dave DeLong Over a year ago

+1 for noticing why it wasn't working! I just thought he had forgotten to turn his string into a predicate.

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