QueryEndingAtValue function does not work correctly in Swift firebase

Question

I have been implementing code that is to enable paging scroll to fetch data by a certain amount of data from firebase database.

Firstly, then error says

Terminating app due to uncaught exception 'InvalidQueryParameter', reason: 'Can't use queryEndingAtValue: with other types than string in combination with queryOrderedByKey'

The below here is the actual code that produced the above error

static func fetchPostsWith(last_key: String?, completion: @escaping (([PostModel]?) -> Void)) {

    var posts = [PostModel]()
    let count = 2

    let ref = Database.database().reference().child(PATH.all_posts)
    let this_key = UInt(count + 1)
    let that_key = UInt(count)

    let this = ref.queryOrderedByKey().queryEnding(atValue: last_key).queryLimited(toLast: this_key)
    let that = ref.queryOrderedByKey().queryLimited(toLast: that_key)

    let query = (last_key != nil) ? this : that

    query.observeSingleEvent(of: .value) { (snapshot) in
        if snapshot.exists() {
            for snap in snapshot.children {
                if let d = snap as? DataSnapshot {
                    let post = PostModel(snapshot: d)
                    print(post.key ?? "")
                    posts.append(post)
                }
            }
            posts.sort { $0.date! > $1.date! }
            posts = Array(posts.dropFirst())
            completion(posts)
        } else {
            completion(nil)
        }
    }
}

What it tries to do is to fetch a path where all posts are stored by auto id. But the error keeps coming out so I do not know what is wrong. Do you have any idea?

 func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
    // index is the last and last fetched then
    print(self.feeds.count - 1 == indexPath.row, "index ", self.hasFetchedLastPage, "has fetched last")
    if self.feeds.count - 1 == indexPath.row {
        let lastKey = self.feeds[indexPath.row].key
        if lastKey != self.previousKey {
            self.getFeeds(lastKey: lastKey)
        } else {
            self.previousKey = lastKey ?? ""
        }
    }
    print("Cell Display Number", indexPath.row)
}

func getFeeds(lastKey: String?) {
    print(self.isFetching, "is fetching")
    guard !self.isFetching else {
        self.previousKey = ""
        return
    }
    self.isFetching = true
    print(self.isFetching, "is fetching")
    FirebaseModel.fetchPostsWith(last_key: lastKey) { ( d ) in
        self.isFetching = false
        if let data = d {
            if self.feeds.isEmpty { //It'd be, when it's the first time.
                self.feeds.append(contentsOf: data)
                self.tableView.reloadData()
                print("Initial Load", lastKey ?? "no key")
            } else {
                self.hasFetchedLastPage = self.feeds.count < 2
                self.feeds.append(contentsOf: data)
                self.tableView.reloadData()
                print("Reloaded", lastKey ?? "no key")
            }
        }
    }
}

I want to implement a paging enabled tableView. If you can help this code to be working, it is very appreciated.

Answer 1

You're converting your last_key to a number, while keys are always strings. The error message tells you that the two types are not compatible. This means you must convert your number back to a string in your code, before passing it to the query:

let this = ref.queryOrderedByKey().queryEnding(atValue: last_key).queryLimited(toLast: String(this_key))
let that = ref.queryOrderedByKey().queryLimited(toLast: String(that_key))