Question

I have an NSManagedObject called WorkOrder with a boolean property isComplete defined in a category for that class.

I use an NSFetchedResultsController to fetch these from the data store and display them in a table view. I’d like to be able to filter the results based on the isComplete property, but of course the predicate in the NSFetchedResultsController can’t do that because the property is not a Core Data attribute. I also can’t filter the controller’s fetchedObjects array because that property is read-only.

Is there any way to do what I’m trying to do without rolling my own data structure that mimics NSFetchedResultsController but allows me to filter the results post-fetch?

Answer 1

As I said in the comments for Adam Eberbach’s answer, I solved this using an NSDictionary (self.workOrdersByDate, below) to store the grouped results, as well as an NSArray (self.dateSections, below) to store the sorted keys of the dictionary.

// Fetch all the WorkOrders
NSArray *results = [WorkOrder findAll];

// Filter based on isComplete property
NSPredicate *filter;
if (self.segmentedStatus.selectedSegmentIndex == SegmentAssigned) {
    filter = [NSPredicate predicateWithFormat:@"isComplete == 0"];
} else {
    filter = [NSPredicate predicateWithFormat:@"isComplete == 1"];
}
results = [results filteredArrayUsingPredicate:filter];

// Retain an NSArray of sorted NSDate keys
self.dateSections = [[results valueForKeyPath:@"@distinctUnionOfObjects.scheduledStartDate.beginningOfDay"] sortedArrayUsingSelector:@selector(compare:)];

// Create the dictionary
self.workOrdersByDate = [[NSMutableDictionary alloc] initWithCapacity:self.dateSections.count];
for (int sectionNum = 0; sectionNum < self.dateSections.count; sectionNum++) {
    NSPredicate *sectionPredicate = [NSPredicate predicateWithFormat:@"scheduledStartDate.beginningOfDay == %@", [self.dateSections objectAtIndex:sectionNum]];
    NSArray *workOrdersForSection = [results filteredArrayUsingPredicate:sectionPredicate];
    [resultsDict setObject:workOrdersForSection forKey:[self.dateSections objectAtIndex:sectionNum]];
}