SWIFT: Data model for "Like" button functionality in iOS app - ios

Question

I'm creating a playlist app (Mock-Up Below) using Swift and Parse. Each user has the ability add a song (or multiple songs) to the TableView and "Like" or "Dislike" (toggle style) as many songs as they like, including their own. This functionality is very similar to the Instagram "Like" button behaviour.
I'm having a bit of trouble conceptualizing the data model. As shown below, I have a User table and a Playlist table (with all of the added songs):
User Table:
Playlist Table:
I'm having trouble with the next step, which is storing the "Like" data for each user and each song.
UPDATED: I've added a column in the 'PlaylistData' table in Parse called "userVotes". As you can see, I'm appending all of the data into an array called 'voters'. For some reason, I'm getting a fatal run time error - 'fatal error: unexpectedly found nil while unwrapping an Optional value'.
import UIKit
import Parse
class MusicPlaylistTableViewController: UITableViewController {
var usernames = [String]()
var songs = [String]()
var voters = [String]()
var numVotes = 0
override func viewDidLoad() {
super.viewDidLoad()
tableView.separatorColor = UIColor.grayColor()
let query = PFQuery(className:"PlaylistData")
query.findObjectsInBackgroundWithBlock { (objects: [PFObject]?, error: NSError?) -> Void in
if error == nil {
if let objects = objects! as? [PFObject] {
self.usernames.removeAll()
self.songs.removeAll()
self.voters.removeAll()
for object in objects {
let username = object["username"] as? String
self.usernames.append(username!)
let track = object["song"] as? String
self.songs.append(track!)
self.voters = object["userVotes"] as! [String]
print(self.voters)
}
self.tableView.reloadData()
}
} else {
print(error)
}
}
}
override func viewWillAppear(animated: Bool) {
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
// MARK: - Table view data source
override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
// #warning Incomplete implementation, return the number of sections
return 1
}
override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
// #warning Incomplete implementation, return the number of rows
return usernames.count
}
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("CellTrack", forIndexPath: indexPath) as! TrackTableViewCell
cell.username.text = usernames[indexPath.row]
cell.songTitle.text = songs[indexPath.row]
cell.votes.text = "\(numVotes)"
cell.selectionStyle = UITableViewCellSelectionStyle.None
return cell
}
override func tableView(tableView: UITableView, didDeselectRowAtIndexPath indexPath: NSIndexPath) {
}
}
I've also created a TableViewCell swift file for the prototype cell:
import UIKit
import Parse
class TrackTableViewCell: UITableViewCell {
var numVotes = 0
#IBOutlet weak var songTitle: UILabel!
#IBOutlet weak var username: UILabel!
#IBOutlet weak var votes: UILabel!
#IBAction func voteButton(sender: UIButton) {
self.numVotes = self.numVotes + 1
self.votes.text = "\(self.numVotes)"
}
}
At this point, all it does is when the heart is clicked, it increases the vote count by 1 on screen (the user can do this as many times as possible, no data is stored in the database). What I need help with is the best way to implement table(s) which allow me to keep track of which users have voted for each song (or not). I know I need a TRUE / FALSE column somewhere, but I can't seem to figure out how to model it. Any suggestions or links to SWIFT tutorials would be greatly appreciated. A simple explanation on what tables to create (or what columns to add to existing tables) would help the best. Thanks!