Thank you both for your suggestions. I ended up going with Ken's idea regarding the synthetic property. It was added to a NSManagedObject derived class so I couldn't use it during the fetch request without actually adding an attribute but I did use it to sort the resulting array. The synthetic property computes an priority index when invoked. It performs very well.
-Michael On Feb 8, 2011, at 5:19 PM, Ernesto Giannotta wrote: > > On 07-feb-2011, at 16:29, Ken Thomases wrote: > >> On Feb 7, 2011, at 8:56 AM, Michael Crawford wrote: >> >>> I'm trying to implement a feature where I sort a cross-section of music >>> from multiple genres with up to two different keys, where the items with a >>> genre matching the first key appear first in the collection and items with >>> a genre matching the second key appear after the first group in the >>> collection. All songs with a genre not matching the first or second keys >>> can be in any order following the first two groups. >>> >>> So I took a look at NSSortDescriptor but it is not apparent to me how I >>> would accomplish my goal with this class. If I sort with it based on the >>> genre key, will basically sort them in alphabetical ascending or descending >>> order, not what I want. >> >> Here are two possible approaches: >> >> 1) Implement a synthetic property which is more amenable to the sort >> ordering you want. Something which returns 0 for the first genre, 1 for the >> second, and 2 for all others, for example. >> >> 2) Implement a custom comparator method that compares the existing genre >> property in the manner you want: the first genre equal to itself but coming >> before all others; the second genre coming after the first, equal to itself, >> and coming before the remaining genres; all other genres coming after the >> first two but unordered with respect to each other. >> >> Either or both of these methods could be implemented in a category if that >> makes things easier. >> > > Or subclass the NSSortdescriptor and implement > > - (NSComparisonResult)compareObject:(id)object1 toObject:(id)object2 > > > Cool Runnings, > Erne. > _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) 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 arch...@mail-archive.com
