Firebase Checking for Null Value (Swift)

Firebase checking for null value (Swift)

Take advantage of the exists() method to determine if the snapshot contains a value. To use your example:

let uid = ref.authData.uid
ref.queryOrderedByChild("uid").queryEqualToValue(uid)
         .observeSingleEventOfType(.Value, withBlock: { snapshot in

    guard snapshot.exists() else{
        print("User doesn't exist")
        return
    }

    print("User \(snapshot.value) exists")
})

.

Here's another handy example, Swift4

    let path = "userInfo/" + id + "/followers/" + rowId

    let ref = Database.database().reference(withPath: path)

    ref.observe(.value) { (snapshot) in

            let following: Bool = snapshot.exists()

            icon = yesWeAreFollowing ? "tick" : "cross"
        }

Checking if Firebase snapshot is equal to nil in Swift

There are a few things going on here, but the most important one is that you cannot test for the existence of children with .ChildAdded. That makes sense if you think about it: the .ChildAdded event is raised when a child is added to the location. If no child is added, the event won't be raised.

So if you want to test if a child exists at a location, you need to use .Value. Once you do that, there are various way to detect existence. Here's one:

ref.queryOrderedByChild("waiting").queryEqualToValue("1")
   .observeEventType(.Value, withBlock: { snapshot in
       print(snapshot.value)
       if !snapshot.exists() {
           print("test2")
       }
   });

Swift 3 getting nil value in firebase while retrieving data

Reload your table view after appending the data to array:

func retriveData() {
    ref.observe(.childAdded, with: { (snapshot) in

        if let snapshot = snapshot.children.allObjects as? [DataSnapshot] {

            for snap in snapshot {
                if let userDict = snap.value as? Dictionary<String,AnyObject> {
                    print("user dict - \(String(describing: userDict["name"]))")
                    let username = userDict["name"] as? String
                    self.uname.append(username!)
                }
            }
                tableView.reloadData()

        }
    })
}

Firebase for SWIFT iOS: returning nil value in function

You need to use closures as getDocument() does not return synchronously.

func display(userid: String, handler: (String) -> Void) {
    let docRef = db.collection("user").document(uid)
    docRef.getDocument { (document, error) in
        if let document = document, document.exists {
            if let displayName = document.get("username") as? String {
                handler(displayName)
            }
        } else {
            print("Document does not exist")
        }
    }
}

And use it like so:

self.myLabel.text = "Loading..."
display(userid: {USER_ID}) { [weak self] displayName in
    print(displayName)
    self.myLabel.text = displayName
}

how to check if Database is empty swift 3 - Firebase

For that you need to check snapshot children count first, whether it's empty or not.

For that -

var ref = Firebase(url: FIREBASE_URL)
ref.observeEventType(.Value, withBlock: { (snapshot: FDataSnapshot!) in
    if(snapshot.childrenCount > 0){ // It has value already

   }
  else{ // Still Empty 

    // Upload values to firebase

   }
})

Hope it will help you to achieve what you want. :)

Firebase on Swift, how to get notified if a query is empty?

you can check if the snapshot exist, this will return a Bool

snapshot.exists()

swift firestore cannot check if documents value nil is

I would say that you would better like to make a safe check, alltogether with casting the type like so:

if let decisions = document.get("decisions") as? [String: String] {
    object.decisions = decisions
}

Firebase Snapshot equal to null when value exists

There may be other issues with the code but I would suggest a different approach. Instead of a tight loop to read in the reviews about each post, just include the post_id in each review and then a simple query to read them in.

Posts
  "post_id_0" : { //childByAutoId()
      "endTime" : "05:32 PM 27/07/2018",
      "imageUrl" : "",
      "live" : true,
      "locationName" : "",
      "postTitle" : "hahahahaha ",
      "reviews" : {
        "review_id_0" : true,
        "review_id_1" : true
      },
      "startTime" : "04:32 PM 27/07/2018",
      "views" : 0

ReviewPost
    "review_id_0" : { //childByAutoId()
      "post_id": "post_id_0", //a reference to the post
      "addPostID" : "-LIQ_Aa8s1H067wFeCdR",
      "rating" : 5,
      "reviewComment" : "Dumplings were rubbish.",
      "time" : "2018-08-28 04:58:18 +0000",
      "userID" : "LUtRmkAefPNsRjPni5Dn0KAvKBx1"
    },

then to get all of the reviews for post_id_0

let reviewPostRef = self.ref.child("ReviewPost")
let query = reviewPostRef.queryOrdered(byChild: "post_id").queryEqual(toValue: "post_id_0")
query.observeSingleEvent(of: .value, with: { snapshot in
    for child in snapshot.children {
        let childSnap = child as! DataSnapshot
        let dict = childSnap.value as! [String: Any]
        let comment = dict["reviewComment"] as! String
        print(comment)
    }
})

and the output is

Dumplings were rubbish.

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