Document.swift

import Foundation
import CoreData

class Document : NSManagedObject {
    
    class func newDocument() -> Document {
        return self.documentForID("1")
    }
    class func documentForID(documentID: String) -> Document {
        let predicate = NSPredicate(format: "documentID = %@", documentID)
        return self.findFirstOrInsert(predicate).then(onQueue: dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {$0 as Document}).wait()!
    }
    
    @NSManaged var documentID:String
    @NSManaged var notes:[Note]
    @NSManaged var createdAt:NSDate
    @NSManaged var updatedAt:NSDate
    
    override func awakeFromInsert() {
        super.awakeFromInsert()
        self.createdAt = NSDate()
        self.updatedAt = NSDate()
    }
    
    override func willSave() {
        super.willSave()
        let currentTime = NSDate()
        if currentTime.timeIntervalSinceDate(self.updatedAt) > 1.0 {
            self.updatedAt = currentTime
        }
    }
}

Promise+wait.swift

extension Promise {
    func wait(_ timeInterval: NSTimeInterval = 5.0) -> T? {
        if let v = self.value {
            return v
        }
        var v: T? = nil
        self.handlers.append({
            v = self.value
        })
        NSThread.sleepForTimeInterval(timeInterval)
        return v
    }
}