how to read firebase database - swift

Question

This is my data structure: many clubs, each club has address. I tried to make the database flat.
Now I want to load a few club info on table view. When I swipe down iPhone screen, it will load next a few club info.
This is my code. But it loads all club info. How can I load only a few club, and load next a few club when user swipe down?
func loadClubs() {
ref = Database.database().reference()
ref.child("club").observe(DataEventType.value, with: { (snapshot) in
//print("clubs: \(snapshot)")
let array:NSArray = snapshot.children.allObjects as NSArray
for obj in array {
let snapshot:DataSnapshot = obj as! DataSnapshot
if let childSnapshot = snapshot.value as? [String: AnyObject] {
if let clubName = childSnapshot["name"] as? String {
print(clubName)
}
}
}
})
}

Answer 1

Firebase's queries support pagination, but it's slightly different from what you're used to. Instead of working with offsets, Firebase uses so-called anchor values to determine where to start.
Getting the items for the first page is easy, you just specify a limit to the number of items to retrieve:
ref = Database.database().reference()
query = ref.child("club").queryOrderedByKey().limitToFirst(10)
query.observe(DataEventType.value, with: { (snapshot) in
Now within the block, keep track of the key of the last item you've shown to the user:
for obj in array {
let snapshot:DataSnapshot = obj as! DataSnapshot
if let childSnapshot = snapshot.value as? [String: AnyObject] {
lastKey = childSnapshot.key
if let clubName = childSnapshot["name"] as? String {
print(clubName)
}
}
}
Then to get the next page, construct a query that starts at the last key you've seen:
query = ref.child("club").queryOrderedByKey().startAt(lastKey).limitToFirst(11)
You'll need to retrieve one more item than your page size, since the anchor item is retrieve in both pages.

Answer 2

i think the right way make reference to array of elements,
and make variable for index
var i = 0;
var club = null;
club = loadClubs(index); // here should return club with specified index;
// and increment index in loadClubs func,
// also if you need steped back --- and one more
// argument to function, for example
// loadClubs(index, forward) // where forward is
// boolean that says in which way we should
// increment or decrement our index
so in your example will be something like this:
func loadClubs(index, forward) {
ref = Database.database().reference()
ref.child("club").observe(data => {
var club = data[index];
if(forward){
index ++
}else{
index--
}
return club;
})
}