This is an update listener class to automatically update insertDate and updateDate properties for Core Data. This Gist is meant for one of my blog posts: http://www.rugenheidbuchel.be/2015/08/03/core-data-update-listener-in-swift/ Note that there is a Swift 2 and a Swift 3 version!

UpdateListener-swift2.swift

//
//  UpdateListener.swift
//  CoreDataUpdateListener
//
//  Created by Rugen Heidbuchel on 03/08/15.
//  Updated by Rugen Heidbuchel on 03/10/15.
//  Copyright © 2015 Rugen Heidbuchel. All rights reserved.
//

import CoreData

/**
An abstract class that listens to Core Data's update notifications to set the insertDate and updateDate properties.
*/
class UpdateListener {
    
    
    // MARK: Settings
    
    /// Indicates whether UpdateListener should print updates to the console.
    static var loggingEnabled = true
    
    
    
    // MARK: Property Names
    var insertDateProperty = "insertDate"
    var updateDateProperty = "updateDate"
    
    
    
    // MARK: Singleton
    
    /// A shared UpdateListener
    static let sharedInstance = UpdateListener()
    
    /// Sets up the shared instance of UpdateListener.
    static func setupSharedInstance() {
        UpdateListener.sharedInstance
    }
    
    
    
    // MARK: Init
    
    init() {
        NSNotificationCenter.defaultCenter().addObserver(self, selector: "managedObjectContextWillSave:", name: NSManagedObjectContextWillSaveNotification, object: nil)
    }
    
    
    
    // MARK: Notifications
    
    /**
    This gets called when a managed object context will save. It updates all insertDate and updateDate properties.
    */
    @objc func managedObjectContextWillSave(notification: NSNotification) {
        // Get the managed object context from the notification
        let managedObjectContext = notification.object as! NSManagedObjectContext
        
        // Loop through the set of inserted and updated managed objects
        for managedObject in managedObjectContext.updatedObjects.union(managedObjectContext.insertedObjects) {
            
            // If it has an insertDate property, update it
            if managedObject.inserted && managedObject.entity.attributesByName[insertDateProperty] != nil {
                managedObject.setValue(NSDate(), forKey: insertDateProperty)
                
                if UpdateListener.loggingEnabled {
                    print("Updated \(insertDateProperty) for entity of name: \(managedObject.entity.name!)")
                }
            }
            
            // If it has an updateDate property, update it
            if managedObject.updated && managedObject.entity.attributesByName[updateDateProperty] != nil {
                managedObject.setValue(NSDate(), forKey: updateDateProperty)
                
                if UpdateListener.loggingEnabled {
                    print("Updated \(updateDateProperty) for entity of name: \(managedObject.entity.name!)")
                }
            }
        }
    }
}

UpdateListener.swift

//
//  UpdateListener.swift
//  CoreDataUpdateListener
//
//  Created by Rugen Heidbuchel on 03/08/15.
//  Updated by Rugen Heidbuchel on 03/10/15.
//  Copyright © 2015 Rugen Heidbuchel. All rights reserved.
//

import CoreData

/**
An abstract class that listens to Core Data's update notifications to set the insertDate and updateDate properties.
*/
class UpdateListener {
    
    
    // MARK: Settings
    
    /// Indicates whether UpdateListener should print updates to the console.
    static var loggingEnabled = true
    
    
    
    // MARK: Property Names
    var insertDateProperty = "insertDate"
    var updateDateProperty = "updateDate"
    
    
    
    // MARK: Singleton
    
    /// A shared UpdateListener
    static let sharedInstance = UpdateListener()
    
    /// Sets up the shared instance of UpdateListener.
    static func setupSharedInstance() {
        let _ = UpdateListener.sharedInstance
    }
    
    
    
    // MARK: Init
    
    init() {
        NotificationCenter.default.addObserver(
            self,
            selector: #selector(UpdateListener.managedObjectContextWillSave(_:)),
            name: NSNotification.Name.NSManagedObjectContextWillSave,
            object: nil)
    }
    
    
    
    // MARK: Notifications
    
    /**
    This gets called when a managed object context will save. It updates all insertDate and updateDate properties.
    */
    @objc func managedObjectContextWillSave(_ notification: Notification) {
        // Get the managed object context from the notification
        let managedObjectContext = notification.object as! NSManagedObjectContext
        
        // Loop through the set of inserted and updated managed objects
        for managedObject in managedObjectContext.updatedObjects.union(managedObjectContext.insertedObjects) {
            
            // If it has an insertDate property, update it
            if managedObject.isInserted && managedObject.entity.attributesByName[insertDateProperty] != nil {
                managedObject.setValue(Date(), forKey: insertDateProperty)
                
                if UpdateListener.loggingEnabled {
                    print("Updated \(insertDateProperty) for entity of name: \(managedObject.entity.name!)")
                }
            }
            
            // If it has an updateDate property, update it
            if managedObject.isUpdated && managedObject.entity.attributesByName[updateDateProperty] != nil {
                managedObject.setValue(Date(), forKey: updateDateProperty)
                
                if UpdateListener.loggingEnabled {
                    print("Updated \(updateDateProperty) for entity of name: \(managedObject.entity.name!)")
                }
            }
        }
    }
}

Thanks for making this! Hey, what do you think about doing this at NSManagedObjectContextObjectsDidChangeNotification instead of WillSaveNotification?

@Adlai-Holler: Sorry for the (2-years) late response! I guess my notifications weren't as good back then as they are now...

I looked into the NSManagedObjectContextObjectsDidChangeNotification, but I guess it would make the process a bit more complex. That notification is only called when objects are changed, not when they are added to the context. This means we would still need the other notification to set the insertDate property. I can't really tell how it would affect performance without testing it, so maybe I will do that in the near future. It would be good to test the performance impact anyhow...

It's nice to know that you like it by the way, so thanks for letting me know!