How to get follower and following count quickly with Firebase and Swift - swift

Question

I am currently trying to fetch all the followers for a specific user with firebase. In my didSet clause, I call the function setFollowingCount() to fetch the users that the current user follows and assign it to a text field:
var user: User? {
didSet {
setFollowingCount()
guard let following = self.user?.following else {return}
let attributedText = NSMutableAttributedString(string: "\(following)\n", attributes: [NSAttributedStringKey.font: UIFont.boldSystemFont(ofSize: 14)])
attributedText.append(NSAttributedString(string: "followers", attributes: [NSAttributedStringKey.foregroundColor: UIColor.lightGray, NSAttributedStringKey.font: UIFont.systemFont(ofSize: 14)]))
self.followingLabel.attributedText = attributedText
}
}
The setFollowingCount() function is:
func setFollowingCount(){
var i = 0
guard let userId = self.user?.uid else { return }
Database.database().reference().child("following").child(userId).observe(.value) { (snapshot) in
self.user?.following = Int(snapshot.childrenCount)
}
}
The problem is that this takes very long to load and often freezes the entire app when you look at a user's profile. How can I speed this up or make it work more efficiently?

Answer 1

self.user?.following = Int(snapshot.childrenCount)
Is not an efficient solution. .childrenCount actually loops over the snapshot and counts all of the children which is going to be slow.
Instead you want to store the number of followers as a single value you can retrieve it faster.
following: {
uid: {
followingCount: 100,
follwersCount: 150
}
}
Then you can query like this:
Database.database().reference().child("following").child(userId).observeSingleEvent(of: .value) { (snapshot) in
if let counts = snap.value as? [String: AnyObject] }
let followingCount = counts["followingCount"] as? Int
let followersCount = counts["followersCount"] as? Int
// save these values somewhere
}
})
I would also recommend you increment / decrement the follower counts in a transaction block so the count doesn't get messed up. That can look something like this:
static func incrementCount(countName: String) {
if let uid = Auth.auth().currentUser?.uid {
let databaseReference = Database.database().reference()
databaseReference.child("following").child(uid).runTransactionBlock { (currentData: MutableData) -> TransactionResult in
if var data = currentData.value as? [String: Any] {
var count = data[countName] as! Int
count += 1
data[countName] = count
currentData.value = data
return TransactionResult.success(withValue: currentData)
}
return TransactionResult.success(withValue: currentData)
}
}
}
Lastly,
If you're going to use .observe you need to remove the reference. In this case though you aren't looking for updates so you can use .observeSingleEvent