I don't know about the others, but I know that @max and @min work on
NSTimestamps too.
Also, I should have said that the recursion works like normal
recursion: toward the end of the keypath until it hits the end of the
keypath, then back out to the front of the keypath. Specifically,
for valueForKeyPath("A.B.C") it calls valueForKey("A").valueForKeyPath
("B.C"). valueForKeyPath("B.C") calls valueForKey
("B").valueForKeyPath("C") which turns into valueForKey("C") at C.
source.valueForKeyPath("[EMAIL PROTECTED]") works by putting a
conditional in NSArray's implementation of valueForKeyPath.
source.valueForKey("people").valueForKeyPath("@sum.somefield")
valueforKey("people") returns a plain old NSArray full of people
the source object calls valueForKeyPath("@sum.somefield") on that array
NSArray takes the next token which is "@sum". It sees it a special
operator, takes it out of the keypath, and calls valueForKeyPath
("somefield") on each element in the array, then accumulates the
total and returns it.
(if it was not an operator it would simply return an array composed
of the results of valueForKeyPath("somefield") on each element in the
array)
I probably got that wrong somewhere :-)
John
On Aug 29, 2006, at 4:20 PM, John Larson wrote:
Hello,
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 PROTECTED]" ) - but that's still
wrong. You can only provide toOne keyPaths after @sum it seems
(i.e., "[EMAIL PROTECTED]" ) which will succeed
(having now tested).
You can think of the keypath as a tokenized string that is
evaluated recursively through the elements toward the end of the
string and the @operators are looking for scalar values to iterate
over and accumulate. So, for company.people.account.totalLiability
where people is the only array, then
[EMAIL PROTECTED] would produce the sum as
desired. Suppose, however, that each person had multiple
accounts. The following would also be valid:
[EMAIL PROTECTED]@sum.totalLiability.
The point of this was to not leave the thread with the idea that
there can only be one @operator in a keypath.
John
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