Not Able to append the documents retrieved - ios

Question

I am not able to append the documents retrieved from the Firestore database in chat application based on Swift IOS to the "messages" variable, after appending I have configure the table cells as below in the code, I am getting the following error
Error
Cannot convert value of type '[QueryDocumentSnapshot]' to expected argument type 'DocumentSnapshot'
Code
var messages: [DocumentSnapshot]! = []
func configuredatabase ()
{
db.collection("messages").document("hello").collection("newmessages").document("2").collection("hellos").document("K").collection("messages").addSnapshotListener { querySnapshot, error in
guard let documents = querySnapshot?.documents else {
print("Error fetching documents: \(error!)")
return
}
//here is the error
self.messages.append(documents)
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
// Dequeue cell
let cell = self.clientTable .dequeueReusableCell(withIdentifier: "tableViewCell", for: indexPath)
// Unpack message from Firebase DataSnapshot
let messageSnapshot = self.messages![indexPath.row]
guard let message = messageSnapshot as? [String:String] else { return cell }
let name = message[Constants.MessageFields.name] ?? ""
if let imageURL = message[Constants.MessageFields.imageURL] {
if imageURL.hasPrefix("gs://") {
Storage.storage().reference(forURL: imageURL).getData(maxSize: INT64_MAX) {(data, error) in
if let error = error {
print("Error downloading: \(error)")
return
}
DispatchQueue.main.async {
cell.imageView?.image = UIImage.init(data: data!)
cell.setNeedsLayout()
}
}
} else if let URL = URL(string: imageURL), let data = try? Data(contentsOf: URL) {
cell.imageView?.image = UIImage.init(data: data)
}
cell.textLabel?.text = "sent by: \(name)"
} else {
let text = message[Constants.MessageFields.text] ?? ""
cell.textLabel?.text = name + ": " + text
cell.imageView?.image = UIImage(named: "ic_account_circle")
if let photoURL = message[Constants.MessageFields.photoURL], let URL = URL(string: photoURL),
let data = try? Data(contentsOf: URL) {
cell.imageView?.image = UIImage(data: data)
}
}
return cell
}

Answer 1

While there are two other very good answers, there may be some confusion between a
FIRDocumentSnapshot (Note: renamed to DocumentSnapshot)
Which is returned when you want to get a specific document: someDoc.getDocument(
and
FIRQuerySnapshot (Note: renamed to QuerySnapshot)
Which is returned when an observer is added to a collection or a series of documents is being retrieved: someCollection.getDocuments and then each document within QuerySnapshot is a discreet FIRQueryDocumentSnapshot (renamed to QueryDocumentSnapshot). (e.g. iterate over the QuerySnapshot to get the child QueryDocumentSnapshot)
Note that DocumentSnapshot may return nil in data property if the document doesn't exists, so it can be tested for .exists. Whereas QueryDocumentSnapshot will never be nil (exists is always true) because deleted data is not returned.
In the question, an observer is being added to a collection with
.collection("messages").addSnapshotListener
therefore the data returned is a QuerySnapshot and to store it as a var, the var type would need to match
var messagesQuerySnapshot: QuerySnapshot!
and then inside the listener
db.collection("messages")...addSnapshotListener { querySnapshot, error in
messagesQuerySnapshot = querySnapshot
However, I would not recommend that.
I would suggest a messages class that can be initialize with the data retrieved from Firestore and store those in an array.
class MessagesClass {
var msg_id = ""
var msg = ""
var from = ""
convenience init(withQueryDocSnapshot: QueryDocumentSnapshot) {
//init vars from the document snapshot
}
}
and then a class var datasource array to hold them
var messagesArray = [MessageClass]()
and then code to read the messages, create the message objects and add them to the dataSource array
db.collection("messages")...getDocuments { querySnapshot, error in
guard let snapshot = querySnapshot else {
print("Error fetching snapshots: \(error!)")
return
}
for doc in snapshot.documents {
let aMsg = MessageClass(withQueryDocSnapshot: doc)
self.messagesArray.append(aMsg)
}
}
NOTE: we are not adding an listener here, we are getting the documents one time. If you want to add a listener to watch for users being added, changed or removed, additional code is needed to detect the changes.
See the Firebase Documentation on Viewing Changes Between Snapshots

Answer 2

Replace self.messages.append(documents) with self.messages.append(contentsOf: documents)
The first method takes a single element and the second one takes a collection which is in your case.
https://developer.apple.com/documentation/swift/array/3126937-append
https://developer.apple.com/documentation/swift/array/3126939-append

Answer 3

var messages: [[String: Any]] = []
db.collection("messages").document("hello").collection("newmessages").document("2").collection("hellos").document("K").collection("messages").addSnapshotListener { querySnapshot, error in
guard let documents = querySnapshot?.documents else {
print("Error fetching documents: \(error!)")
return
}
for doc in documents {
self.messages.append(doc.data())
}
}