Querying and updating votes with Parse? - ios

Question

I am trying to set up a voting system Parse as my backend.
I want to use swipe left and right as the voting method and I am using a query.getObjectInBackgroundWithID so that I can update the vote count to my backend.
I am having trouble querying it and also saving the votes in the back and having that append in to the cell so that the vote count will be added on the tableview cells.
Keep on receiving this error in my log for the query:
no results matched the query (Code: 101, Version: 1.7.2)
How can I correct this? Also How can I make the voting system work after I get the query to work and update the backend?
Here is my code so far:
import UIKit
import Parse
class HomePage: UITableViewController {
let post = PFObject(className: "Post")
var images = [UIImage]()
var titles = [String]()
var imageFile = [PFFile]()
var voteCounter = 0
var count = [Int]()
override func viewDidLoad() {
super.viewDidLoad()
println(PFUser.currentUser())
var query = PFQuery(className:"Post")
query.orderByDescending("createdAt")
query.limit = 15
query.findObjectsInBackgroundWithBlock {(objects: [AnyObject]?, error: NSError?) -> Void in
if error == nil {
println("Successfully retrieved \(objects!.count) scores.")
println(objects!)
if let objects = objects as? [PFObject] {
for object in objects {
if let title = object["Title"] as? String {
self.titles.append(title)
}
if let imgFile = object["imageFile"] as? PFFile {
self.imageFile.append(imgFile)
}
if let voteCounter = object["count"] as? Int {
self.count.append(voteCounter)
}
self.tableView.reloadData()
}
} else {
// Log details of the failure
println(error)
}
}
}
}
/* println("Successfully retrieved \(objects!.count) scores.")
for object in objects! {
self.titles.append(object["Title"] as! String)
self.imageFile.append(object["imageFile"] as! PFFile)
self.tableView.reloadData()
}*/
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
return 1
}
override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return titles.count
}
override func tableView(tableView: UITableView, heightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
return 500
}
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
var myCell:cell = self.tableView.dequeueReusableCellWithIdentifier("myCell") as! cell
myCell.rank.text = "21"
myCell.votes.text = "\(count)"
myCell.postDescription.text = titles[indexPath.row]
imageFile[indexPath.row].getDataInBackgroundWithBlock { (data, error) -> Void in
if let downloadedImage = UIImage(data: data!) {
myCell.postedImage.image = downloadedImage
}
}
var swipeRight = UISwipeGestureRecognizer(target: self, action: "respondToSwipeGesture:")
swipeRight.direction = UISwipeGestureRecognizerDirection.Right
myCell.postedImage.userInteractionEnabled = true;
myCell.postedImage.addGestureRecognizer(swipeRight)
var swipeLeft = UISwipeGestureRecognizer(target: self, action: "respondToSwipeGesture:")
swipeRight.direction = UISwipeGestureRecognizerDirection.Left
myCell.postedImage.userInteractionEnabled = true;
myCell.postedImage.addGestureRecognizer(swipeLeft)
This is the query that I get errors on:
var query = PFQuery(className:"Post")
query.getObjectInBackgroundWithId("count") {
(Post: PFObject?, error: NSError?) -> Void in
if error != nil {
println(error)
} else if let Post = Post {
Post["count"] = self.voteCounter
Post.saveInBackground()
}
}
return myCell
}
func respondToSwipeGesture(gesture: UIGestureRecognizer) {
if let swipeGesture = gesture as? UISwipeGestureRecognizer {
switch swipeGesture.direction {
case UISwipeGestureRecognizerDirection.Right:
voteCounter += 1
println("Swiped right")
case UISwipeGestureRecognizerDirection.Left:
voteCounter -= 1
println("Swiped Left")
default:
break
}
}
}
}
Also here is my Parse backend:
ive added the new code now
import UIKit
import Parse
class HomePage: UITableViewController {
let post = PFObject(className: "Post")
var images = [UIImage]()
var titles = [String]()
var imageFile = [PFFile]()
var votingObjects: [PFObject] = []
override func viewDidLoad() {
super.viewDidLoad()
println(PFUser.currentUser())
println(PFUser.currentUser())
var query = PFQuery(className:"Post")
query.orderByDescending("createdAt")
query.limit = 15
query.findObjectsInBackgroundWithBlock {
(objects: [AnyObject]?, error: NSError?) -> Void in
if error == nil {
println("Successfully retrieved \(objects!.count) scores.")
println(objects!)
for objectRaw in objects! {
let object = objectRaw as! PFObject
self.votingObjects.append(object)
// Adding them to the array
if let title = object["Title"] as? String {
self.titles.append(title)
}
if let imgFile = object["imageFile"] as? PFFile {
self.imageFile.append(imgFile)
}
}
dispatch_async(dispatch_get_main_queue(), {
self.tableView.reloadData()
// Updating the tableView on the main thread - important. Do some research on Grand Central Dispatch :)
})
} else {
println(error)
// Error
}
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
return 1
}
override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return titles.count
}
override func tableView(tableView: UITableView, heightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
return 500
}
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
var myCell:cell = self.tableView.dequeueReusableCellWithIdentifier("myCell") as! cell
myCell.rank.text = "21"
i cant figure out whats the right code here for the myCell.votes.text to =
myCell.votes.text = votingObjects[indexPath.row]["count"] as? String
myCell.postDescription.text = titles[indexPath.row]
imageFile[indexPath.row].getDataInBackgroundWithBlock { (data, error) -> Void in
if let downloadedImage = UIImage(data: data!) {
myCell.postedImage.image = downloadedImage
}
}
var swipeRight = UISwipeGestureRecognizer(target: self, action: "respondToSwipeGesture:")
swipeRight.direction = UISwipeGestureRecognizerDirection.Right
myCell.postedImage.userInteractionEnabled = true;
myCell.postedImage.addGestureRecognizer(swipeRight)
var swipeLeft = UISwipeGestureRecognizer(target: self, action: "respondToSwipeGesture:")
swipeRight.direction = UISwipeGestureRecognizerDirection.Left
myCell.postedImage.userInteractionEnabled = true;
myCell.postedImage.addGestureRecognizer(swipeLeft)
return myCell
}
having an issue here:
func respondToSwipeGesture(gesture: UIGestureRecognizer) {
if let swipeGesture = gesture as? UISwipeGestureRecognizer {
switch swipeGesture.direction {
case UISwipeGestureRecognizerDirection.Right:
updateVote(true, objectId: String())
println("Swiped right")
case UISwipeGestureRecognizerDirection.Left:
updateVote(false, objectId: String())
println("Swiped Left")
default:
break
}
}
}
func updateVote(increment: Bool, objectId : String) {
// Create a pointer to an object of class Posts with id 'objectId'
var object = PFObject(withoutDataWithClassName: "Post", objectId: objectId)
// Increment the current value of the quantity key by 1
if increment == true {
object.incrementKey("count", byAmount: 1)
} else {
object.incrementKey("count", byAmount: -1)
}
// Save
object.saveInBackgroundWithBlock(nil)
}
}
but i keep recieving the error of cannot update without specific objectId whenever i swipe and initiate the gesture recognizer. i also cant figure out how to display the votes in my cell

Answer 1

It looks like you are querying the Parse db for an objectID which doesn't exist. This is because when you receive the objects, the attribute "count" is the number of votes right... but when you query for an object, you are using "count" as the objectID which obviously won't work. Your idea of using the variable count will also not work.
What I would recommend is a slight adjustment in your structures.
When receiving the objects from the initial query, store them in an array of Parse Objects. This way, you retain all of their information and it will be much easier to update them. The will also provide an attribute object.objectId which is a String, which is what you will need when querying the db again.
Another tip is Parse supports an increment function when dealing with a column of type number
Also, when working on background threads, you should make any UI calls on the main thread using GCD.
Code:
Initial query -
var votingObjects: [PFObject] = []
override func viewDidLoad() {
super.viewDidLoad()
println(PFUser.currentUser())
var query = PFQuery(className:"Post")
query.orderByDescending("createdAt")
query.limit = 15
query.findObjectsInBackgroundWithBlock {
(objects: [AnyObject]!, error: NSError!) -> Void in
if error == nil {
println("Successfully retrieved \(objects!.count) scores.")
println(objects!)
for objectRaw in objects {
let object = objectRaw as! PFObject
self.votingObjects.append(object) // Adding them to the array
}
dispatch_async(dispatch_get_main_queue(), {
self.tableView.reloadData() // Updating the tableView on the main thread - important. Do some research on Grand Central Dispatch :)
})
} else {
// Error
}
}
}
// Pass true if you want to upvote or false if downvote
func updateVote(increment: Bool, objectId : String) {
// Create a pointer to an object of class Posts with id 'objectId'
var object = PFObject(withoutDataWithClassName: "Posts", objectId: objectId)
// Increment the current value of the quantity key by 1
if increment == true {
object.incrementKey("count", byAmount: 1)
} else {
object.incrementKey("count", byAmount: -1)
}
// Save
object.saveInBackgroundWithBlock(nil)
}
}
Your tableView functions will all link to the array now..
numberOfRows will simply use votingObjects.count
TitleForRow will use votingObject[indexPath.row]["Title"]! // Should be 'title'
And any time you want to refer to a voting objects ID, you simply use votingObject[index].objectId
Hope I didn't miss anything :)