The example of countries is just that, an example. The actual app is about
something else. Also, the color of the text is not a model property - the
selected status is.
I think you didn't quite understand what the problem I'm having is. The problem
is that NSFetchedResultsController is ignoring a transformable attribute used
as a sorting key.
On Feb 10, 2011, at 2:10 PM, claw wrote:
> hi,
>
> i want you to propose just an idea , a remark, ....on apple documentation is
> said
>
> The NSFetchRequest class is used to describe search criteria used to retrieve
> data from a persistent store..... implicitely you must record all of them and
> update them sometimes....
>
> in your idea there is a lot of different kind of countries ( india, honduras
> ....) which can have a common property: a selected color that can vary a lot
> of times....
>
> why not trying to use an Hash Table in order to use weak reference with
> NSHashTable ??....instead of each time ask core data to update all the entire
> store....
>
> best regards
>
>
>
>
> Le 10 févr. 2011 à 16:19, WT a écrit :
>
>> Hello list,
>>
>> a little while ago I posted a question regarding some strange behavior by an
>> NSFetchedResultsController (under the same subject line as this message).
>> Since then I've narrowed the problem down a bit more and now have a test
>> project to show it.
>>
>> Here's what the goal is, in a nutshell.
>>
>> I have a list of, say, countries. Some are "selected", others not. I need to
>> display all the countries in the same tableview, in the same section, and
>> what differentiates the selected ones from the deselected ones is their text
>> color. Moreover, the selected ones should be sorted ascending by their
>> "index" (an integer that's used to keep track of their position in the list)
>> while the deselected ones must be sorted ascending by their "name".
>>
>> The test project's core data model has a single entity, "CountryCD", with
>> the attributes "name", "index", "selected" (representing a boolean), and a
>> transformable attribute "indexOrName" which returns the entity's index if
>> it's selected or its name if it's deselected.
>>
>> - (id) indexOrName;
>> {
>> if ([self.selected isEqualToNumber: [NSNumber numberWithBool: YES]])
>> {
>> return self.index;
>> }
>> else
>> {
>> return self.name;
>> }
>> }
>>
>> The fetched results controller is defined as usual but contains two sort
>> descriptors:
>>
>> NSSortDescriptor* sortBySelected = [[NSSortDescriptor alloc]
>> initWithKey: @"selected" ascending: NO];
>>
>> NSSortDescriptor* sortByIndexOrName = [[NSSortDescriptor alloc]
>> initWithKey: @"indexOrName" ascending: YES];
>>
>> the idea being that entities get sorted first by their "selected" status and
>> then by their "indexOrName" attribute. Since that attribute returns the
>> entity's "index" or its "name", depending on the entity's "selected" status,
>> the fetched results controller *should* sort the entities as desired.
>>
>> Should, but doesn't. And that's the problem I can't seem to solve.
>>
>> In the test project, I create country entities in the following order
>>
>> [self createCountryOfName: @"India"];
>> [self createCountryOfName: @"Honduras"];
>> [self createCountryOfName: @"Germany"];
>> [self createCountryOfName: @"Denmark"];
>> [self createCountryOfName: @"Brazil"];
>> [self createCountryOfName: @"Egypt"];
>> [self createCountryOfName: @"Australia"];
>> [self createCountryOfName: @"China"];
>> [self createCountryOfName: @"Finland"];
>>
>> and make every second one deselected, which *should* result in them being
>> displayed as follows:
>>
>> // (ordered by index)
>> // India
>> // Germany
>> // Brazil
>> // Australia
>> // Finland
>>
>> // (ordered by name)
>> // China
>> // Denmark
>> // Egypt
>> // Honduras
>>
>> Alas, they're displayed like this (or some other seemingly random order):
>>
>> (selected)
>> Brazil
>> Germany
>> Australia
>> India
>> Finland
>>
>> (deselected)
>> Honduras
>> Denmark
>> Egypt
>> China
>>
>> Neither the selected ones are sorted by their "index" attribute nor the
>> deselected ones are sorted by their "name" attribute. In fact, the test
>> project shows that "indexOrName" is not accessed at all when the fetched
>> results controller does its fetch.
>>
>> First I thought that there might be something wrong with the way I
>> implemented the fetched results controller, but if you replace "indexOrName"
>> in the sort descriptor with either "index" or "name", it works as would be
>> expected.
>>
>> So then I thought that using a transformable attribute is not the way to go
>> in order to achieve the result I need to achieve, but I can't see any other
>> way to do it.
>>
>> If using a transformable attribute isn't the way to go, can anyone suggest
>> an alternative? If using a transformable attribute should work, then why
>> doesn't it as I've implemented it? It appears to me that
>> NSFetchedResultsController ignores a sort descriptor based on a
>> transformable attribute.
>>
>> The test project can be found here:
>> http://www.restlessbrain.com/FRC_Test.zip
>>
>> I'd greatly appreciate any help. I've already spent several days trying to
>> figure this out but got nowhere and ran out of ideas.
>>
>> Thanks in advance.
>> WT
>>
>> _______________________________________________
>>
>> Cocoa-dev mailing list ([email protected])
>>
>> Please do not post admin requests or moderator comments to the list.
>> Contact the moderators at cocoa-dev-admins(at)lists.apple.com
>>
>> Help/Unsubscribe/Update your Subscription:
>> http://lists.apple.com/mailman/options/cocoa-dev/clawfr59%40yahoo.fr
>>
>> This email sent to [email protected]
>
_______________________________________________
Cocoa-dev mailing list ([email protected])
Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com
Help/Unsubscribe/Update your Subscription:
http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com
This email sent to [email protected]
