Documents fetched are replacing the previous loaded documents in tableview - ios

Question

I am using the below code to fetch the data from the firestore database in swift iOS. But when I scroll the new data loaded is replacing the previously loaded data in the tableview. I am trying to fix this issue but as of now no good.
The outcome required is that adding new documents to the previously list of documents in the tableview
Below is the code I am implementing. If any more information is required please let me know
CODE
fileprivate func observeQuery() {
fetchMoreIngredients = true
//guard let query = query else { return }
var query1 = query
stopObserving()
if posts.isEmpty{
query1 = Firestore.firestore().collection("posts").order(by: "timestamp", descending: true).limit(to: 5)
}
else {
query1 = Firestore.firestore().collection("posts").order(by: "timestamp", descending: true).start(afterDocument: lastDocumentSnapshot).limit(to: 2)
// query = db.collection("rides").order(by: "price").start(afterDocument: lastDocumentSnapshot).limit(to: 4)
print("Next 4 rides loaded")
print("hello")
}
// Display data from Firestore, part one
listener = query1!.addSnapshotListener { [unowned self] (snapshot, error) in
guard let snapshot = snapshot else {
print("Error fetching snapshot results: \(error!)")
return
}
let models = snapshot.documents.map { (document) -> Post in
if let model = Post(dictionary: document.data()) {
return model
} else {
// Don't use fatalError here in a real app.
fatalError("Unable to initialize type \(Post.self) with dictionary \(document.data())")
}
}
self.posts = models
self.documents = snapshot.documents
if self.documents.count > 0 {
self.tableView.backgroundView = nil
} else {
self.tableView.backgroundView = self.backgroundView
}
self.tableView.reloadData()
self.fetchMoreIngredients = false
self.lastDocumentSnapshot = snapshot.documents.last
}
}
func scrollViewDidScroll(_ scrollView: UIScrollView) {
let off = scrollView.contentOffset.y
let off1 = scrollView.contentSize.height
if off > off1 - scrollView.frame.height * leadingScreensForBatching{
if !fetchMoreIngredients && !reachEnd{
print(fetchMoreIngredients)
// beginBatchFetch()
// query = baseQuery()
observeQuery()
}
}
}

Answer 1

Instead of calling snapshot.documents, call snapshot.documentChanges. This returns a list of document changes (either .added, .modified, or .removed, and allows you to add, remove, or modify them in your local array as needed... Not tested code just an idea what you ca do ...
snapshot.documentChanges.forEach() { diff in
switch diff.type {
case .added:
if let model = Post(dictionary: diff.document.data()){
self.posts.append(model)
}else {
// Don't use fatalError here in a real app.
fatalError("Unable to initialize type \(Post.self) with dictionary \(document.data())")
}
case .removed:
// add remove case
case .modified:
// add modify case
}
}