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?
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.
来源：https://stackoverflow.com/questions/13325849/sorting-on-transient-fields-with-nsfetchedresultcontroller