Re: NSPredicate and nil variables.
Re: NSPredicate and nil variables.
- Subject: Re: NSPredicate and nil variables.
- From: Todd Blanchard <email@hidden>
- Date: Wed, 6 Jul 2005 21:28:39 -0700
Instead of trying to put nil into NSDictionary, you can use the
placeholder [NSNull null] if you are explicitly searching for an
object with a property that has a nil value. This is not the same as
saying the property can have any value though.
On Jul 6, 2005, at 9:06 PM, Óscar Morales Vivó wrote:
Aha, so as I understand it since NSDictionary won't contain nil
that means it isn't possible to create a predicate with
substitution variables if any of them is nil.
I'm just a young padawan when it comes to Cocoa it seems. Should
have thought of that. :P
Anyway at least I know now exactly how it behaves (and it also
means I'll have to do a lot of checking for nil in my code)
Thanks for the insight.
Oscar Morales Vivo.
On Jul 6, 2005, at 23:14 , mmalcolm crawford wrote:
On Jul 6, 2005, at 5:19 PM, Óscar Morales Vivó wrote:
I've understood how to build predicates with variables, how to
instantiate them and do fetch requests on them. However I'm not
sure how the predicate will behave if any of the predicate's
variables ends up being nil, especially for things like dates
where I'm not sure how a zero would be interpreted.
Do you mean you want to use predicateWithSubstitutionVariables?
<http://developer.apple.com/documentation/Cocoa/Conceptual/
Predicates/Articles/pCreating.html#//apple_ref/doc/uid/
TP40001793-219639-BCIIHDCH>
"To create a valid predicate to evaluate against an object, you
use the NSPredicate method predicateWithSubstitutionVariables: to
pass in a dictionary that contains the variables to be
substituted. (Note that the dictionary must contain key-value
pairs for all the variables specified in the predicate.)"
(That constraint should be mentioned in the API reference...)
mmalc
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