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: Chuck Hill <email@hidden>
- Date: Tue, 29 Aug 2006 14:37:32 -0700
On Aug 29, 2006, at 2:20 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@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).
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@hiddenLiability would produce the sum as
desired. Suppose, however, that each person had multiple
accounts. The following would also be valid:
email@hiddenemail@hiddenLiability.
Now _that_ is some clever thinking!
The point of this was to not leave the thread with the idea that
there can only be one @operator in a keypath.
And I will also add that it is quite easy to hook into KVC to
implement your own "magic" operators. IIRC, there are some quite
interesting things in Wonder as well as WOOgnl.
Chuck
--
Practical WebObjects - for developers who want to increase their
overall knowledge of WebObjects or who are trying to solve specific
problems. http://www.global-village.net/products/practical_webobjects
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