I've just found out that some code that seemed to be working fine
doesn't do so under all circumstances.
I have a to-many relationship (called 'elements') in a managed object
('parent').
In one spot in my code, there is a need to obtain and present all of
the elements of the parent managed object, which I already have in my
hand.
The parent MO is defined with an 'elements' property (nominally an
NSSet). So for simply reading the set and converting it to an array,
I had imagined the following would be OK:
NSArray *elements = [parent.elements allObjects];
Now, this turns out to be bad, as on occasion (and I think, when there
are no elements), I get the error:
*** -[NSCFArray allObjects]: unrecognized selector sent to instance
<whatever>
It's interesting to see that the receiver here turns out to be an
array! I'm aware that the to-many relationship is likely to be
represented by a faulting proxy object, but this was unexpected.
I'm assuming this is exposing a poor assumption on my part regarding
how Core Data works with to-many relationships under all conditions.
What should I be doing here instead? I could presumably enumerate
through the collection (no matter what flavour it currently exists in,
this should work in all circumstances included the 'no elements' case).
The docs certainly contain a lot of info about accessing to-many
relationships (where particular care is needed to change the set of
objects in a to-many relationship correctly), but I don't recollect
anything telling me that I couldn't treat the to-many relationship as
a set when simply looking up which objects are there.
Cheers
-- lwe
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