CoreDataFetchRequest.swift

//Source (http://christiantietze.de/posts/2015/10/results-from-fetch-requests/)


import Foundation
import CoreData

enum CoreDataError: ErrorType {
    case InconsistentCoreDataFetchRequestResults
}

class CoreDataFetchRequest<T: NSManagedObject> {

    let fetchRequest: NSFetchRequest

    var predicate: NSPredicate? {
        get { return fetchRequest.predicate }
        set { fetchRequest.predicate = newValue }
    }

    convenience init(entityName: String) {
    
        self.init(fetchRequest: NSFetchRequest(entityName: entityName))
    }

    init(fetchRequest: NSFetchRequest) {
    
        self.fetchRequest = fetchRequest
    }

    func executeInContext(context: NSManagedObjectContext) throws -> [T] {
    
        let results = try context.executeFetchRequest(fetchRequest)
    
        guard let properResults = results as? [T] else {
            throw CoreDataError.InconsistentCoreDataFetchRequestResults
        }
    
        return properResults
    }
}