I think this is the solution:
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setEntity: [NSEntityDescription entityForName: @"Person"
inManagedObjectContext: context]];
[fetchRequest setPredicate: [NSPredicate predicateWithFormat: @"name IN
%@", [persons valueForKey:@"name"]]];
[fetchRequest setResultType: NSDictionaryResultType];
NSError *error;
NSArray *personsMatchingNames = [context executeFetchRequest:
fetchRequest error: &error];
NSMutableArray *uniqueNames = [NSMutableArray arrayWithArray: persons];
[uniqueNames removeObjectsInArray: personsMatchingNames];
I also had to set the resulttype of the fetchrequest to NSDictionaryResultType.
Thanks all for the help.
- Koen.
On Oct 15, 2012, at 11:51 AM, Keary Suska <cocoa-...@esoteritech.com> wrote:
>
> 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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