distinctUnionOfSets operator with mutableSetValueForKeyPath:?
distinctUnionOfSets operator with mutableSetValueForKeyPath:?
- Subject: distinctUnionOfSets operator with mutableSetValueForKeyPath:?
- From: "Jeremy Higgs" <email@hidden>
- Date: Thu, 2 Nov 2006 16:42:15 +1100
Hi all,
I'm in the process of moving an application towards bindings and
CoreData (well, it's mostly done). However, I'm having an issue with
some array/set operators and Key-Value Coding.
I've got an object with the following relationships (and cardinality marked):
Object A (1) --- (M) Object B (1) --- (M) Object C
That is, Object A can have many instances of Object B, and Object B
can have many instances of Object C.
What I'm trying to do (in an accessor method) is achieve this:
Object A (1) --- (M) Object C
In my accessor method, I have the following:
- (NSSet *)allObjectC;
{
return [self valueForKeyPath:@"email@hiddentC"];
}
This works fine. As I understand it, the valueForKeyPath: call above
works in the following way:
1) Calls [self valueForKey:@"objectB"] on objectA (which returns a set)
2) For each of the objects in the set, valueForKey:@"objectC" is called
3) The results of 2) are aggregated into a set and returned. (So
there's a set containing instances of Object C.)
I've got tests for this, so am confident that's what the result is.
However, if I want to retrieve a mutable set containing those objects
(mutableSetValueForKeyPath:), I have problems using the
@distinctUnionOfSets operator. The following is the "mutable" version
of the method I pasted above:
- (NSMutableSet *) allObjectC;
{
return [self mutableSetValueForKeyPath:@"objectB.@distinctUnionOfSets.
objectC"];
}
Calling this method results in the following message:
[<NSCFSet 0x5f99b10> valueForUndefinedKey:]: this class is not key
value coding-compliant for the key distinctUnionOfSets.
As far as I can see, there's nothing in the documentation (
http://tinyurl.com/ylh9ck ) that says you can't use the set and array
operators with mutableSetValueForKeyPath: .
Funnily enough, the what is returned by the "immutable" use of
valueForKeyPath: appears to be a mutable set. This contrasts the KVC
documentation (http://tinyurl.com/yloj3c ):
"The default implementation recognizes the same simple accessor
methods and set accessor methods as valueForKey:, and follows the same
direct instance variable access policies, but always returns a mutable
collection proxy object instead of the immutable collection that
valueForKey: would return."
Am I misunderstanding some of the concepts here, or is it a problem in KVC?
Thanks in advance!
Jeremy
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