On Oct 15, 2012, at 6:23 AM, Koen van der Drift wrote:
> On Mon, Oct 15, 2012 at 8:19 AM, Jerry Krinock <je...@ieee.org> wrote:
>>
>> On 2012 Oct 15, at 03:45, Koen van der Drift <koenvanderdr...@gmail.com>
>> wrote:
>>
>>> So I cannot directly filter an array of dictionaries using a predicate?
>>> That was the whole goal of my question, see my original post.
>>
>> Oh, now I see. I'd assumed that 'persons' was an array. It's a dictionary!
>
> Even better, it's an array of dictionaries! :-)
Willeke probably addressed your issue best. The contents of the collection that
you pass to the aggregate expression must be the same type of value as the left
hand expression. So, to have "name IN {ARRAY}", ARRAY *must* be an array of
"name"s. In most cases, that will be strings. When you pass dictionaries, how
is the predicate to know what value to use from the dictionary? There is no
magic here. Other than how curiously the NSPredicate interpreted the array of
dictionaries. Interesting, but not useful to your purpose. In any case, the
predicate that you have shown is not valid for your case.
Have you tried Willeke's suggestion? If it doesn't work, it doesn't mean that
the predicate is bad, as -predicateWithFormat: is notorious for not working
well with aggregate operations. Jerry Krinock's suggestion of constructing the
predicate manually works most reliably, so that would be your next step to a
solution.
HTH,
Keary Suska
Esoteritech, Inc.
"Demystifying technology for your home or business"
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