Directly, yes. NSExpression stores a keypath as a single string, whereas
variables are store in their own kind of NSExpression object. When you replace
variables with new values, it's only looking for the certain kinds of
NSExpression objects to replace. Everything else stays the same.
Some notes about your predicate:
- I'm not sure you can do "$x isKindOfClass: %@" as the predicate to a
subquery, although I haven't tried it. If it doesn't work, you could do this
with a FUNCTION ("FUNCTION($x, 'ks_isKindOfClass:', %@)"). Note, however, that
you'd have to create a category on NSObject that simply boxes the return value
of isKindOfClass into an NSNumber. FUNCTION()'s don't like methods that return
primitives.
- If you want to use a keypath with a variable, you could do:
FUNCTION($x, 'text') CONTAINS[cd] $searchString
That preserves $x as a variable expression so that it will be replaced properly.
This would make your entire predicate:
SUBQUERY(events, $x, FUNCTION($x, 'ks_isKindOfClass:', %@) AND (FUNCTION($x,
'text') CONTAINS[cd] $searchString)).@count != 0
Dave
On Mar 16, 2011, at 11:20 AM, Kyle Sluder wrote:
> Hi all,
>
> Is it really impossible to create an NSExpression of the form
> "$variableName.someKeyPath"? I can create an NSExpression for
> $variableName, and I can create an NSExpression for someKeyPath, but I
> can't create one that contains both.
>
> The actual problem is that I'm trying to create an NSPredicate for
> "SUBQUERY(events, $x, $x isKindOfClass: %@ AND $x.text CONTAINS[cd]
> $searchString).@count != 0". Since the method in question is called
> periodically (it's the action method of a filter control), I was
> hoping to create a static variable-based NSPredicate, rather than
> reconstruct the predicate every time this method gets called. But that
> didn't work because it didn't descend into the subquery's subpredicate
> to replace $searchString.
>
> --Kyle Sluder
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