Re: Proper place for functions in KVC paths?
Re: Proper place for functions in KVC paths?
- Subject: Re: Proper place for functions in KVC paths?
- From: Lachlan Deck <email@hidden>
- Date: Tue, 29 Aug 2006 11:47:31 +1000
Hi there,
On 26/08/2006, at 5:32 AM, Chuck Hill wrote:
On Aug 24, 2006, at 5:57 PM, Lachlan Deck wrote:
On 22/08/2006, at 2:53 AM, Chuck Hill wrote:
On Aug 21, 2006, at 7:59 AM, John Huss wrote:
It seems that key-value coding allows serveral different ways of
using
functions (like @sum, @avg, etc) in key paths that all seem to
work.
Like,
@sum.array.key.path
email@hidden
array.key.path.@sum
Is there a proper way to write these?
I am surprised that these all work. The NSArray documentation
implies :-) the that intended use is
<keyPath to array>@<operator>.<keyPath to value>
I think the api implies they all work and will have differing
outcomes depending on what you would like to 'sum' or 'count' etc.
e.g., Consider the keypath: 'company.people.accounts.totalLiability'.
If I want to know how much is owed in total:
Number total = ( Number )company.valueForKeyPath
( "@sum.people.accounts.totalLiability" );
I am curious if you have actually used this?
Obviously not enough! Bummer...
I meant company.valueForKeyPath
( "email@hiddenLiability" ) - but that's still wrong.
You can only provide toOne keyPaths after @sum it seems (i.e.,
"email@hiddenLiability" ) which will succeed (having now
tested).
These operators are for NSArray (out of the box, sans Wonder) and
it appears that company is an EO, not an NSArray. Thus, I would
expect the above statement to produce a runtime error with an
unknown key of @sum.
Correct.
If I would like to know how much each person owes:
NSArray totals = ( NSArray )group.valueForKeyPath
( "email@hiddenLiability" );
I am also unclear on how that would evaluate. people.valueForKeyPath
("accounts.totalLiability") should, I think, produce an array of
arrays. Is @sum able to handle that correctly?
Unfortunately not. I spoke presumptuously and in haste...sorry about
that. It seems to me, however, that this would be the desired
behaviour. i.e., for the resulting array to contain the elements that
are the sum of the inner arrays.
with regards,
--
Lachlan Deck
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