Search for users that haven't been fetch yet - swift

Question

I have a quick question, I build a block of code that fetches all the users in the database for searching purposes. Preparing for thousands of users in the future, I programmed the method in a pagination way fetching a certain amount of users at a time. That is where the problem lies when I search for a user if the user hasn't been retrieve from the database yet through scrolling I can't search there profile. Does anyone have a suggestion on how I can tackle this?
Here is the code I use to fetch the users:
//create a method that will fetch a certain mount of users
func fetchUsers() {
if userCurrentKey == nil {
USER_REF.queryLimited(toLast: 21).observeSingleEvent(of: .value) { (snapshot) in
self.collectionView?.refreshControl?.endRefreshing()
guard let first = snapshot.children.allObjects.first as? DataSnapshot else { return }
guard let allObjects = snapshot.children.allObjects as? [DataSnapshot] else { return }
allObjects.forEach({ (snapshot) in
let uid = snapshot.key
Database.fetchUser(with: uid, completion: { (user) in
self.users.append(user)
self.collectionView?.reloadData()
})
})
self.userCurrentKey = first.key
}
} else {
USER_REF.queryOrderedByKey().queryEnding(atValue: userCurrentKey).queryLimited(toLast: 22).observeSingleEvent(of: .value, with: { (snapshot) in
guard let first = snapshot.children.allObjects.first as? DataSnapshot else { return }
guard let allObjects = snapshot.children.allObjects as? [DataSnapshot] else { return }
allObjects.forEach({ (snapshot) in
let uid = snapshot.key
if uid != self.userCurrentKey {
Database.fetchUser(with: uid, completion: { (user) in
self.users.append(user)
self.collectionView?.reloadData()
})
}
})
self.userCurrentKey = first.key
})
}
}
}
Here is the code I used to paginate the users:
//once the users pass a certain amount of cells paginate to fetch the next set of users
override func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
if users.count > 20 {
if indexPath.item == users.count - 1 {
print("Fetching...")
fetchUsers()
}
}
}
Lastly here is the code I used to filter through the users:
func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
if searchText.isEmpty{
//if search text is empty fetch the users but display nothing
inSearchMode = false
filteredUsers = users
self.collectionView?.refreshControl = refreshController
} else {
//if search text is not empty search for the users
inSearchMode = true
self.collectionView?.refreshControl = nil
filteredUsers = self.users.filter { (user) -> Bool in
return user.username.lowercased().contains(searchText.lowercased())
}
}
//reload the table view data to update the displayed user
self.collectionView?.reloadData()
}
Thank you in advance!

Answer 1

The up front issue is you should not be in a situation where you have to load all users to search through them.
If you have a lot of data in the users node, loading that much data can overwhelm the device and secondly it's going to get very laggy for the user as the loaded data is iterated over.
Your best move is to denormalize your data and let the server do the heavy lifting by performing those queries and delivering only the data you need. Way faster and much easier to maintain. You can also add additional nodes to get to the data you want.
Looking at the code (I don't know your structure) it appears your goal is to have a searchfield where the users can type a username and the goal is to query for that username and return it lowercased.
A solution is to update your Firebase structure. Suppose it's like this
users
uid_0
userName: "MyCrazyUserNAME"
if you want to search, lowercased, add another node to your structure that's a lowercased version of the name
users
uid_0
userName: "MyCrazyUserNAME"
lowerCased: "mycrazyusername"
Then, perform a partial string query on the lowerCased node as the user types
func searchFor(thisPartialString: String) {
let userRef = self.ref.child("users")
let startString = thePartialString
let endString = thisPartialString + "\\uf8ff"
let query = ref.queryOrdered(byChild: "lowerCased")
.queryStarting(atValue: startString)
.queryEnding(atValue: endString")
query.observe....
}
The "\uf8ff" is a character at a very high code level in Unicode - because of that it encompasses all of the preceeding characters.