Am 12.03.2010 um 17:32 schrieb Eli Bach:
> On Mar 12, 2010, at 5:37 AM, Alexander Spohr wrote:
>
>> Am 12.03.2010 um 04:34 schrieb Eli Bach:
>>
>>> The operators mentioned on this page, particularly "@unionOfSets".
>>>
>>> <http://developer.apple.com/mac/library/documentation/cocoa/Conceptual/KeyValueCoding/Concepts/ArrayOperators.html>
>>>
>>> I have the following Core Data object's setup
>>>
>>> ClassA ClassB ClassC
>>> relationA --> relationB --> relation C
>>>
>>> where each of the relations is a many to one [one class A, many class B,
>>> and one class B, many class C].
>>> Not all ClassB's will have ClassC objects attached to them
>>>
>>> I have an instance of classA, and I want an NSArrayController with all the
>>> ClassC objects for all the ClassB objects that are related to that specific
>>> instance of ClassA, preferably in a way that uses KVO instead of
>>> programmatically updating with fetches/predicates/etc.
>>>
>>> What would be the right way to bind the NSArrayController, assuming the nib
>>> owner has an instance of classA:
>>
>> How about Owner.instanceOfA.relationB.relationC ?
>> If you ask an array for a key path you get a new array containing the
>> resulting objects.
>> You don’t need any operators.
>
> I'll try this, but I don't expect it to work, because there can be 0 or more
> relationB object's, and each of those object's can have 0 or more relationC
> objects, and just 'plain' dot syntax won't produce a superset of relationC
> objects
If you have 0 Bs, you’ll have an empty array
If you have Bs without Cs they just wont fill anything into the array.
*methinks* it might be that you get some NSNull in there for the empty Cs.
But no, this should not happen because the relationship itself is an NSSet, not
a pointer that can be nil.
From NSSet’s valueForKey:
Discussion
The returned set might not have the same number of members as the receiver. The
returned set will not contain any elements corresponding to instances of
valueForKey: returning nil (note that this is in contrast with NSArray’s
implementation, which may put NSNull values in the arrays it returns).
valueForKeyPath: is just a recursive or iterative call:
"Discussion
The default implementation gets the destination object for each relationship
using valueForKey: and returns the result of a valueForKey: message to the
final object."
atze
> (from my understanding of KVO and KVC).
what is your understanding of KVC?
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