Using time based transient property with NSFetchedResultsController
I have Event model with startDate and endDate . I want to sort this event to 3 categories.
I made a transient property called status contain above logic and use this as parameter in NSFetchedResultsController
NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: self.managedObjectContext, sectionNameKeyPath: "status", cacheName: nil)
When I run I got this error telling me to use section as sort descriptor.
CoreData: error: (NSFetchedResultsController) The fetched object at index 2 has an out of order section name '1. Objects must be sorted by section name'
I then set this in sort descriptor and got this error, since transient can't be used as sort descriptor.
Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'keypath status not found in entity '
The problem is this section are determine from 2 properties, so it can't be sort by just startDate or endDate , but both.
What is the best way to solve this problem? I have consider making this status non-transient, but this value is updated daily, I think it kind of weird to make it non-transient.
NSFetchedResultsController cannot sort on a transient property if it is backed by SQLite (which is the usual case). The backend has to turn your sort request into a SQL query, and the query won't have access to transient properties. You either have to make status non-transient or you can't use NSFetchedResultsController for this.
See the Core Data Programming Guide: Advanced Topics: Fetch Predicates and Sort Descriptors for more.
In addition you cannot sort on transient properties using the SQLite store.
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