swift PFQueryTableViewController - remove duplicate objects before presenting cells - ios

Question

I have two Classes in Parse, one contains details of images that users have liked ("Liked"), the second class lists users that are following other users ("Follows").
In my PFQueryViewController I am able to create a query in queryForTable() that does the following:
//get username of users being followed
let query:PFQuery = PFQuery(className:"Follows")
query.whereKey("fromUser", equalTo: (PFUser.currentUser()?.username)!)
//get images of all followed users
let imageQuery:PFQuery = PFQuery(className: "Liked")
imageQuery.whereKey("username", matchesKey: "toUser", inQuery: query)
//get images current user liked
let userImagesQuery:PFQuery = PFQuery(className: "Liked")
userImagesQuery.whereKey("username", equalTo: (PFUser.currentUser()?.username)!)
//combine liked images of following and current user
let combinedQuery:PFQuery = PFQuery.orQueryWithSubqueries([imageQuery,userImagesQuery])
if(objects?.count == 0)
{
combinedQuery.cachePolicy = PFCachePolicy.CacheThenNetwork
}
combinedQuery.orderByDescending("createdAt")
return combinedQuery
This works where I am able to display the liked images of the user, and the users being followed, in cellForRowAtIndexPath by querying the imageID of the object for each cell. However, multiple users can like the same image, so if a user and someone they are following like the same image, the image will appear twice in the table.
Is there a way to force the query to ignore objects when it finds a duplicate based on the ImageID key?
I am aware this can be done by executing the query and iterating through the objects, however this wont work in this scenario as I need the duplicates to be removed before the query is returned in queryForTable().

Answer 1

I managed to solve this by using objectsDidLoad(). This captures the objects before they are sent to the table, therefore I was able to iterate through each object and delete any duplicates.
I store all the loaded objects into a new array and remove an object if a duplicate is found. I then make the object in cellForRowAtIndexPath the corresponding object in the array.
override func objectsDidLoad(error: NSError?) {
super.objectsDidLoad(error)
displayedImages.removeAll()
imageObjects = NSMutableArray(array: objects!)
for item in imageObjects {
if displayedImages.count == 0 {
let image = item["imageid"] as! NSNumber
displayedImages.insert(image, atIndex: 0)
}else{
var count = 0
let image = item["imageid"] as! NSNumber
for imageToCheck in displayedImages {
if imageToCheck != image {
count++
}
}
if count != displayedImages.count {
imageObjects.removeObject(item)
}else{
displayedImages.insert(image, atIndex: 0)
}
}
}
self.tableView.reloadData()
}
override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
// #warning Incomplete implementation, return the number of rows
return imageObjects.count
}
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath, object: PFObject?) -> PFTableViewCell? {
let cell = tableView.dequeueReusableCellWithIdentifier("Cell") as! FeedTableViewCell
if let pfObject:PFObject = self.imageObjects.objectAtIndex(indexPath.row) as? PFObject {
//display images as before