Better NSFetchedResultscontroller

CoreDataFetchController.swift

//
//  CoreDataFetchController.swift
//
//  Created by Scott Grosch on 12/18/14.
//  Copyright (c) 2014 Gargoyle Software, LLC. All rights reserved.
//

import CoreData

final class CoreDataFetchController<T : NSManagedObject> {
    let fetchedResultsController: NSFetchedResultsController
    
    /**
     * Returns a fetch controller initialized using the given fetchedResultsController
     *
     * :param: fetchedResultsController The previously configured NSFetchedResultsController to wrap.
     *
     * :returns: A properly typed CoreDataFetchController
     */
    init(fetchedResultsController: NSFetchedResultsController) {
        self.fetchedResultsController = fetchedResultsController
        try! fetchedResultsController.performFetch()
    }
    
    /**
     * Returns a fetch controller initialized using the given arguments.
     *
     * :param: managedObjectContext The managed object against which fetchRequest is executed.
     * :param: sortDescriptors The sort descriptors of the receiver.
     * :param: predicate The predicate of the receiver.  Defaults to nil.
     * :param: sectionNameKeyPath A key path on result objects that returns the section name. Defaults to nil.
     * :param: cacheName The name of the cache file the receiver should use. Defaults to nil.
     * :param: delegate The delegate for the NSFetchedResultsController.
     * 
     * :returns: A properly typed CoreDataFetchController
     */
    init(managedObjectContext: NSManagedObjectContext, sortDescriptors: [NSSortDescriptor], predicate: NSPredicate? = nil, sectionNameKeyPath: String? = nil, cacheName: String? = nil, delegate: NSFetchedResultsControllerDelegate? = nil) {
        #if DEBUG
            if let sectionNameKeyPath = sectionNameKeyPath {
                assert(sortDescriptors[0].key == sectionNameKeyPath, "First sort descriptor must be the sectionNameKeyPath!")
            }
        #endif
        
        let name = String(T.self)
        let range = name.startIndex ..< name.endIndex
        
        let entityName: String
        if let index = name.rangeOfString(".", options: .BackwardsSearch, range: range, locale: nil) {
            entityName = name.substringFromIndex(advance(index.startIndex, 1))
        } else {
            entityName = name
        }

        let request = NSFetchRequest(entityName: entityName)
        request.sortDescriptors = sortDescriptors
        request.predicate = predicate
        
        fetchedResultsController = NSFetchedResultsController(fetchRequest: request, managedObjectContext: managedObjectContext, sectionNameKeyPath: sectionNameKeyPath, cacheName: cacheName)
        fetchedResultsController.delegate = delegate
        try! fetchedResultsController.performFetch()
    }
    
    // MARK: - Passthrough variables
    
    /**
     * The results of the fetch.
     *
     * The value of the property is nil if performFetch: hasn’t been called.
     *
     * The results array only includes instances of the entity specified by the fetch request (fetchRequest) and that match
     * its predicate. (If the fetch request has no predicate, then the results array includes all instances of the entity
     * specified by the fetch request.)
     *
     * The results array reflects the in-memory state of managed objects in the controller’s managed object context, not
     * their state in the persistent store. The returned array does not, however, update as managed objects are inserted,
     * modified, or deleted.
     */
    var fetchedObjects: [T]? {
        get {
            return fetchedResultsController.fetchedObjects as? [T]
        }
    }
    
    /**
     * The managed object context used to fetch objects.
     *
     * The controller registers to listen to change notifications on this context and properly update its result set and
     * section information.
     */
    var managedObjectContext: NSManagedObjectContext {
        get {
            return fetchedResultsController.managedObjectContext
        }
    }

    // MARK: - Helpers for UITableViewDataSource
    
    /**
     * Tells the data source to return the number of rows in a given section of a table view.  Should
     * be called from tableView(_:numberOfRowsInSection)
     *
     * :param: section An index number identifying a section in tableView.
     * 
     * :returns: The number of rows in section.
     */
    func numberOfRowsInSection(section: Int) -> Int {
        if let s = fetchedResultsController.sections where (s.count - 1) >= section {
            return s[section].numberOfObjects
        } else {
            return 0
        }
    }
    
    /**
     * Asks the data source to return the number of sections in the table view.  Should be called from 
     * numberOfSectionsInTableView(_)
     *
     * :returns: The number of sections the table view should contain.
     */
    func numberOfSections() -> Int {
        return fetchedResultsController.sections?.count ?? 0
    }
    
    // MARK: - Ease of use methods
    
    /**
     * Returns the object at the given index path in the fetch results, cast to the appropriate type.
     * 
     * :param: indexPath An index path in the fetch results.
     *
     * :returns: The object at a given index path in the fetch results, cast to the appropriate type.
     */
    func objectAtIndexPath(indexPath: NSIndexPath) -> T {
        return fetchedResultsController.objectAtIndexPath(indexPath) as! T
    }
    
    /**
     * Returns the object at the indicated row and section.
     *
     * :param: row An index number identifying a row in a UITableView object in a section identified by section.
     * :param: section An index number identifying a section in a UITableView object.
     * 
     * :returns: The object at the given location
     */
    func objectAt(row row: Int, section inSection: Int? = 0) -> T {
        let section = inSection ?? 0
        let indexPath = NSIndexPath(forRow: row, inSection: section)
        return objectAtIndexPath(indexPath)
    }
    
    
    /**
     * Executes the fetch request on the store to get objects.  An error is thrown if the fetch request 
     * specified doesn't include a sort descriptor that uses sectionNameKeyPath.  After executing this method,
     * the fetched objects can be accessed with the property 'fetchedObjects'
     */
    func performFetch() throws {
        try fetchedResultsController.performFetch()
    }
}

Thanks! Glad somebody else is using it. Just updated one line to make Xcode 7.3 happy.