How to retrieve Cloud Firestore documents and display data in a TableView?

Question

I have my data structure: My Firestore Database

As you'll see I have a "Michael 201A" document as well as a "Michael 201B" the idea is to retrieve the fields from these documents and display them in a tableView. Additionally, i would like the tableView to update automatically based off of any new documents that are added to the "Requests" Collection so the tableView data is always populated wit the most recent additions to the firestore database.

Function to retrieve data from FireStore

@IBOutlet weak var tableView: UITableView!

var db: Firestore!

var requestArray = [Request]()


override func viewDidLoad() {
    super.viewDidLoad()

    db = Firestore.firestore()
    tableView.delegate = self
    tableView.dataSource = self
    loadData()
}

    func loadData() {

    db.collection("Requests").whereField("Status", isEqualTo: true).getDocuments() {(querySnapshot, err) in
        if let err = err {
            print("An error occurred\(err)")
        } else{
            self.requestArray = querySnapshot!.documents.compactMap({Request(dictionary: $0.data())})
            print(self.requestArray)
            DispatchQueue.main.async {
                self.tableView.reloadData()
            }
            }


   }
}

I've added a print statement to get a reading of the value but it returns empty.

My tableView functions

extension ResidentAdvisorViewController: UITableViewDelegate {

    func tableView (_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
       print("You tapped me")
   }
}

extension ResidentAdvisorViewController: UITableViewDataSource {

   func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
       // #warning Incomplete implementation, return the number of rows
    return requestArray.count
   }
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

         let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)

        let request = requestArray[indexPath.row]


        cell.textLabel?.text = "\(request.Name)"
        return cell
    }
}

My Request Struct

protocol DocumentSerializable {
init?(dictionary:[String:Any])

}

struct Request {
var Name: String
var Dorm: String
var Room: Int
var Status: Bool
var UID: String
var TimeStamp: Date

var dictionary:[String:Any] {
return [
    "Name":Name,
    "Dorm":Dorm,
    "Room":Room,
    "Status":Status,
    "UID": UID,
    "TimeStamp": TimeStamp
    ]
}

}

extension Request : DocumentSerializable {
init?(dictionary: [String : Any]) {
    guard let name = dictionary["Name"] as? String,
    let dorm = dictionary["Dorm"] as? String,
        let room = dictionary["Room"] as? Int,
        let status =  dictionary["Status"] as? Bool,
        let uid = dictionary["UID"] as? String,
        let timestamp = dictionary["Timestamp"] as? Date
    else { return nil}

    self.init(Name: name, Dorm: dorm, Room: room, Status: status, UID: uid, TimeStamp: timestamp)

} }

As a side note i have checked to ensure my cell identifier matches "cell". Also, when i change the cell text to "Hello World" I am able to get it displayed in my tableView. Any assistance is greatly appreciated thank you.

Answer 1

There's not a whole lot wrong with the code but there are two questions within the question.

1) Why is the value empty

2) How to I populate my dataSource intially and then update it when new documents are added.

Let me address 2) first.

To initially load the data and then watch for future changes, we can uyse the .addSnapshotListener function, and then handle the specific change type within the firebase closure.

func observeAllRequests() {
    let requestsCollection = self.db.collection("Requests")
    let query = requestsCollection.whereField("Status", isEqualTo: true)
    query.addSnapshotListener { querySnapshot, error in
        guard let snapshot = querySnapshot else {
            print("Error fetching snapshots: \(error!)")
            return
        }

        snapshot.documentChanges.forEach { diff in
            if (diff.type == .added) {
                let name = diff.document.get("Name") as? String ?? "No Name"
                print("added: \(name)") //add to your dataSource
            }
            if (diff.type == .modified) {
                let name = diff.document.get("Name") as? String ?? "No Name"
                print("modified: \(name)") //update the request in the dataSource
            }
            if (diff.type == .removed) {
                let name = diff.document.get("Name") as? String ?? "No Name"
                print("removed: \(name)") //remove the request from the dataSource
            }
        }
        //tableView.reloadData()
    }
}

The above code will return all of the documents that match the query. Iterate over the items in the snapshot, with each being either .added, .modified or .removed. The first time the function is called, all differences will be .childAdded which allows you to initially populate the dataSource.

Any document changes after that will be just the document that was changed with the difference being by .added, .modified and .removed.

EDIT:

To address question 1)

The reason the array is empty is because of how the extension is structured - it's pretty much an all or none. Here's how it is now

extension Request : DocumentSerializable {
init?(dictionary: [String : Any]) {
    guard let name = dictionary["name"] as? String
    let dorm = dictionary["Dorm"] as? String,
        let room = dictionary["Room"] as? Int,
        let status =  dictionary["Status"] as? Bool,
        let uid = dictionary["UID"] as? String,
        let timestamp = dictionary["Timestamp"] as? String
    else { return nil}

    self.init(Name: name)
} }

If a field is not found then the entire thing fails and returns nil, and compactMap igores nil so you end up when an empty array. Your structure does not include Timestamp, so it fails.

I would suggest something to protect your code but allow for missing fields. The nil-coalescing operator would work well here

extension Request : DocumentSerializable {
   init?(dictionary: [String : Any]) {
      let name = dictionary["name"] as? String ?? "No Name"
      let room = dictionary["room") as? String ?? "No Room"
      etc