Re: Core Data Fetch Request Template
Re: Core Data Fetch Request Template
- Subject: Re: Core Data Fetch Request Template
- From: Colin Doncaster <email@hidden>
- Date: Mon, 21 Aug 2006 15:14:29 +1000
Hey there -
Does it really make sense to "fetch" the maximum value of a object
stores in the persistent store? I'm assuming you want to retrieve
the object with the maximum value? The way I'd go about doing this
( it might not be the correct way ) without knowing what the maximum
value is, is to do a fetch request with a sort descriptor, then sort
them based on "value" descending, then just use the first index of
the array. If it's sorted correctly that should be the maximum value.
If there is a chance more than one of them matches a max value then
once you've figured out the maximum value ( with the retrieved object
above ) then perform another fetch request finding all objects that
match that value.
Not too sure how you would avoid the two step process when doing a
fetch request. The concept seems slightly different to me as rather
than trying to return the exact data ( as with NSArray ) you're
actually requesting the containers for the data.
I could be wrong though.
Cheers.
On 21-Aug-06, at 9:11 AM, Niels Meersschaert wrote:
I'm trying to see how this is possible to do directly in the
model. I have an entity with several attributes. I'd like to
create a fetch request in the model which is based on an expression
like @max, @sum, etc of one of the attributes of an entity.
However, whenever I try doing this in the model, it won't let me
compile saying the syntax can't be parsed. I've tried using the
predicate builder & selecting expression, but no joy as it says
it's not the correct format. I am able to do the same
functionality with bindings setting my model key path to
@max.attributeName. How can I configure a fetch request in the
model such that I can get all entities whose attribute is the max
like I can in the binding?
Thanks,
Niels
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