FirebaseDatabase -How to Paginate when using a UISearchController - ios

Question

As the user types text into the searchBar the UISearchController has a delegate method to update search results:
func updateSearchResults(for searchController: UISearchController) {
guard let searchText = searchController.searchBar.text?.lowercased() else { return }
Database...usersRef
.queryOrdered(byChild: "username")
.queryStarting(atValue: searchText)
.queryEnding(atValue: searchText+"\u{f8ff}")
.observe( .childAdded, with: { [weak self](snapshot) in
let key = snapshot.key
guard let dict = snapshot.value as? [String: Any] else { return }
let user = User(userId: key, dict: dict)
self?.datasource.append(user)
})
}
That works fine.
When I normally paginate I use this procedure:
var startKey: String?
func handlePaginationForPosts() {
if startKey == nil {
Database...PostsRef
.queryOrderedByKey()
.queryLimited(toLast: 10)
.observeSingleEvent(of: .value, with: { [weak self] (snapshot) in
guard let children = snapshot.children.allObjects.first as? DataSnapshot else { return }
if snapshot.childrenCount > 0 {
for child in snapshot.children.allObjects as! [DataSnapshot] {
let postId = child.key
if child.key != self?.startKey {
guard let dict = child.value as? [String:Any] else { return }
let post = Post(postId: postId, dict: dict)
self?.datasource.insert(post, at: 0)
}
}
self?.startKey = children.key
}
})
} else {
let lastIndex = datasource.count
Database...PostsRef
.queryOrderedByKey()
.queryEnding(atValue: startKey!)
.queryLimited(toLast: 11)
.observeSingleEvent(of: .value, with: { [weak self] (snapshot) in
guard let children = snapshot.children.allObjects.first as? DataSnapshot else { return }
if snapshot.childrenCount > 0 {
for child in snapshot.children.allObjects as! [DataSnapshot] {
let postId = child.key
if child.key != self?.startKey {
guard let dict = child.value as? [String:Any] else { return }
let post = Post(postId: postId, dict: dict)
// I run a check to make sure the datasource doesn't contain the post before adding it
self?.datasource.insert(post, at: lastIndex)
}
}
self?.startKey = children.key
}
})
}
}
The problem here is when running a search I use:
.queryStarting(atValue: searchText)
.queryEnding(atValue: searchText+"\u{f8ff}")
But when paginating a post I use:
.queryOrderedByKey()
.queryEnding(atValue: startKey!) ...
self?.datasource.insert(post, at: lastIndex)
The startKey is the first key in the snapshot.children.allObjects.first and the lastIndex is the datasource.count.
Considering the search query is based on the search text and not a key, how can I paginate when I'm already using .queryEnding(atValue: searchText+"\u{f8ff}") instead of .queryEnding(atValue: startKey!)?
I need to track the key that was pulled from the db so that when I paginate I can run the next set of results from that particular key.

Answer 1

Firebase Database queries can only order/filter on a single property.
So what you can do is filter for the search criteria, and then limit to the firsts N results.
What you can't do is filter for the search criteria, skip the first N results, and get the next page.
The closest you can get, and something regularly done for cases such as this, is retrieve the first 2*N results when you need to show page 2. This wastes some bandwidth though, so you'll have to trade that off against how useful the pagination is.