objective c - Sorting on 'transient' fields with NSFetchedresultController

Question

Is there a way to use a 'transient' field or something like that and in some way sort accordingly with a NSFetchedResultsController. I want to do the following:

I have location of places in a database. When a person opens the list, I want to show the nearest place on top, an then sort accordingly to distance. But clearly,this depends on the users location, so I cannot use a static field. I was hoping to use a transient field, as you can use for the section headers.

Is there anybody who can give a solution or workaround for this situation?

Answer 1

You cannot use a transient property in a fetch request for a SQlite base Core Data store.

See Fetching Managed Objects in the "Core Data Programming Guide":

You cannot fetch using a predicate based on transient properties (although you can use transient properties to filter in memory yourself). ... To summarize, though, if you execute a fetch directly, you should typically not add Objective-C-based predicates or sort descriptors to the fetch request. Instead you should apply these to the results of the fetch.

You can use a transient property for sectionNameKeyPath, but even then you need a first sort descriptor for the sections that is based on a persistent attribute.

So the only workaround is probably to fetch all objects and then sort the fetched array. But then of course you don't have the advantages of a fetched results controller anymore.