I perform a query using firebase to check if there are any objects that have a child with a certain value. The problem is if there are no such objects the code doesn't run. So in the code below if there are no objects that have a child with facebookID that is 17 the rest of the code will never run. Is there a way to determine when a query finds 0 results?
func previousUser(completion:(result:Bool)->Void){
var queryFound = false
print("check if user is previous")
print(UserData.globalfacebookID)
let ref = Firebase(url:"https://amber-torch-556.firebaseio.com/Users")
ref.queryOrderedByChild("facebookID").queryEqualToValue(17).observeSingleEventOfType(.ChildAdded, withBlock: { snapshot in
print(snapshot.childrenCount)
print("query has ran")
UserData.globalparseID = snapshot.key
queryFound = true
completion(result:queryFound)
})
Check your ref to make sure it's valid.
and try this
ref.queryOrderedByChild("facebookID").queryEqualToValue(17)
.observeEventType(.Value, withBlock: { snapshot in
if snapshot.value is NSNull {
print("dude, snapshot was null")
} else {
print(snapshot.key)
}
})
Change .ChildAdded to .Value and then check for NSNull
To check whether a query returns 0 results, you can check the snapshot as following:
if snapshot.exists() {
// write relevant logic here
}
else {
// handle the case when a query finds 0 results
}
In your case,
func previousUser(completion:(result:Bool)->Void){
var queryFound = false
print("check if user is previous")
print(UserData.globalfacebookID)
let ref = Firebase(url:"https://amber-torch-556.firebaseio.com/Users")
ref.queryOrderedByChild("facebookID").queryEqualToValue(17).observeSingleEventOfType(.ChildAdded, withBlock: { snapshot in
if snapshot.exists() {
print(snapshot.childrenCount)
print("query has ran")
UserData.globalparseID = snapshot.key
queryFound = true
completion(result:queryFound)
}
else {
// handle the case where query finds zero(0) results
}
})
Hope this helps !
Related
My datamodel looks as follows :
allcomments
|__$comment_id_5
|__post_id: <post_id_5>
uid
|
|__activity
|__comments
|__$random_activity_id
|__post_id : <post_id_5> //ref to post_id_5 in allcomments
|__comment_id : <comment_id_5> // ref to comment_id_5 in allcomments
My Goal: To check if the user with uid has commented on the post or not. If that person has, then I he can proceed further else he'll be shown something else on the screen. On trying the following query, I am able to only get the callback when a snapshot exists and not otherwise.
FBDataservice.ds.child("allcomments").queryOrdered(byChild: "post_id").queryEqual(toValue: "post_id_5").observeSingleEvent(of: .ChildAdded) { (snapshot) in
if let data = snapshot.value as? DataDict {
let comment = Comment(comId: snapshot.key , comData: data)
self.checkUserHasResponded(completion: { (hasResponded) in
if !hasResponded {
// Never returns it there is nothng
print("You gotta respond first")
} else {
//this part does work
print("Welcome to seeing everything")
}
})
}
}
func checkUserHasResponded(completion: #escaping (Bool) -> ()) {
FBDataservice.ds.REF_USERS.child(uid).child("activity/comments").queryOrdered(byChild: "post_id").queryEqual(toValue: "post_id_5").observeSingleEvent(of: .value) { (snapshot) in
snapshot.exists() ? completion(true) : completion(false)
}
}
I even tried tweaking the architecture this way and query it differently, still nothing work and the program behaves in the same exact way as incase of above.
uid
|
|__activity
|__comments
|__post_id_5 : comment_id_5
and ran this query:
func checkUserHasResponded(completion: #escaping (Bool) -> ()) {
FBDataservice.ds.REF_USERS.child(uid).child("activity/comments").observeSingleEvent(of: .value) { (snapshot) in
snapshot.hasChild("post_id_5") ? completion(true) : completion(false)
}
}
I tried changing .childAdded to .value. It gives the same exact result. Tried changing .observeSingleEvent(of:) to .observe() as well. But nothing helps. I am not sure what exactly is wrong. Check plenty of answers here, none helped. What exactly am I over looking. Thanks for the help.
Use .value instead of .childAdded, that way it the closure is called whether or not the snapshot exists, Just a quick test shows it works.
func checkUserHasResponded() {
let uid = "uid_0"
let commentsRef = dbRef.child(uid).child("activity").child("comments")
commentsRef.queryOrdered(byChild: "post_id")
.queryEqual(toValue: "post_5")
.observeSingleEvent(of: .value) { snapshot in
if snapshot.exists() {
print("post exists")
} else {
print("post not found")
}
}
}
If your structure does not contain a post_id child value that exists then the output is
post not found
So this answer applies to the updated question. The code in the closure will not run if the node you're querying for does not exist because the query is using .childAdded
FBDataservice.ds.child("allcomments").queryOrdered(byChild: "post_id")
.queryEqual(toValue: "post_id_5")
.observeSingleEvent(of: .childAdded) { (snapshot) in
If that's changed to .value, it returns and the code in the closure runs if the node exists. Keeping in mind that you'll want to use
snapshot.exists()
with that as it will be nil if it doesn't.
snapshot.exists() is retaining its value of true when someValue == nil.
I dont know how to reset the snapshot.exists() value after the initial query. How do i set the database call to only be triggered when i call upon it? like removing the observer the proper way?
let ref = Database.database().reference()
ref.child("matches").child("available").queryOrdered(byChild: "opponent_1").queryEqual(toValue: potential_oponnent).observeSingleEvent(of: .value, with: { (snapshot) -> Void in
if (snapshot.exists()) && someValue != nil {
}else {
ref.removeAllObservers()
}
Do i need to use ref.removeObserver(withHandle: ) or ref.removeAllObservers()?
I've Firebase Database where each user has own email and username. How to check unique username? I tried to make it like this, but my code doesn't work properly therefore different users can have the same username
usernameField.isHidden = false
let username:String = self.usernameField.text!
if (usernameField.text?.isEmpty == false){
ref.child("users").queryOrdered(byChild("username").queryEqual(toValue: username).observeSingleEvent(of: .value, with: { snapshot in
if snapshot.exists(){
print("username exist")
}else{
ref.root.child("users").child(userID).updateChildValues(["username": username])
}
})
}
I'm a little bit newbie in Firebase I store email and username for each user like this newUserReference.setValue(["username":String(), "email" : self.emailTextField.text!]). On next view, user can type username in usernameField.text and this value will be added in Firebase Database. But if the next user (user 2) will type the same username like previous user, it must be blocked, because username should be unique
You still need to indicate what property you want to order/filter on with queryOrdered(byChild:):
if (usernameField.text?.isEmpty == false){
ref.child("users").queryOrdered(byChild:"username").queryEqual(toValue: username).observeSingleEvent(of: .value, with: { snapshot in
if snapshot.exists(){
If you're trying to store your user's id on login do this when you receive a successful response to the login:
create a Shared Instance to store the ID
class userDataSource {
var id : String? // variable to store your users ID
static let sharedInstance = PageDataSource() // global access to this dataSource
private init() {}
}
Assign the id a value after successful login
func getIDFromLogin() {
if let user = Auth.auth().currentUser {
print(user.uid)
userDataSource.sharedInstance.id = user.uid
}
}
Then you can do this to view each id:
ref.child("users").observeSingleEvent(of: .value, with: { snapshot in
if let snapshots = snapshot.children.allObjects as? [DataSnapshot] {
for snap in snapshots {
print(snap.key) // you can compare userDataSource.sharedInstance.id to this value
}
}
})
Or if you just want that user's data do this:
ref.child("users").child(userDataSource.sharedInstance.id!).observeSingleEvent(of: .value, with: { snapshot in
if let snapshots = snapshot.children.allObjects as? [DataSnapshot] {
for snap in snapshots {
print(snap)
}
}
})
Edit to answer your question more accurately
Here is an answer more inline with your question. First thing I will recommend is for you to add a table to Firebase that only contains the usernames, and the .uid's that they belong to. You will need to first read through that table to make sure that no one else has that username, then update the table accordingly:
// This function will check through all of the usernames and return a true or false value in the completion handler
func checkUsernames(_ completion: #escaping(_ success: Bool) -> Void) {
ref.child("usernames").observeSingleEvent(of: .value, with: { snapshot in
if let snapshots = snapshot.children.allObjects as? [DataSnapshot] {
for snap in snapshots {
if snap.value == username {
completion(false)
}
}
completion(true)
} else {
completion(true) // TODO: check for errors before setting completion
}
})
}
// this function will set the username values in Firebase
func storeUsername() {
let usernameRef = ref.child("usernames")
usernameRef.updateChildValues(["\(userDataSource.sharedInstance.id!)" : username])
}
}
}
Assuming you have already handled your username variable and set it's value, you will call the functions like this:
checkUsernames({ (success) in
if success {
storeUsername()
// you may also want to update your "users" table here as well
} else { print("Duplicate Username") } // handle alert or something here
})
I am making a completion handler for a function which will return a list of objects. When it return value for first time, it works well. But when any change happen into firebase database and again observe gets called, array size gets doubled up. Why it's getting doubled up?
func getStadiums(complition: #escaping ([Stadium]) -> Void){
var stadiums: [Stadium] = []
let stadiumRef = Database.database().reference().child("Stadium")
stadiumRef.observe(.value, with: { (snapshot) in
for snap in snapshot.children {
guard let stadiumSnap = snap as? DataSnapshot else {
print("Something wrong with Firebase DataSnapshot")
complition(stadiums)
return
}
let stadium = Stadium(snap: stadiumSnap)
stadiums.append(stadium)
}
complition(stadiums)
})
}
And calling like this
getStadiums(){ stadiums
print(stadiums.count) // count gets doubled up after every observe call
}
The code you're using declares stadiums outside of the observer. This means any time a change is made to the value of the database reference, you're appending the data onto stadiums without clearing what was there before. Make sure to remove the data from stadiums before appending the snapshots again:
func getStadiums(complition: #escaping ([Stadium]) -> Void){
var stadiums: [Stadium] = []
let stadiumRef = Database.database().reference().child("Stadium")
stadiumRef.observe(.value, with: { (snapshot) in
stadiums.removeAll() // start with an empty array
for snap in snapshot.children {
guard let stadiumSnap = snap as? DataSnapshot else {
print("Something wrong with Firebase DataSnapshot")
complition(stadiums)
return
}
let stadium = Stadium(snap: stadiumSnap)
stadiums.append(stadium)
}
complition(stadiums)
})
}
This line stadiumRef.observe(.value, with: { (snapshot) in ... actually adding an observer that will be called everytime your stadium data is changed.
Because you called it twice by using getStadiums(){ stadiums ..., the total observer added will be 2.
That makes the line stadiums.append(stadium) called twice in the second call.
My suggestion would be to use stadiumRef.observe() once without calling it from getStadiums().
Create a Model as below
class OrderListModel: NSObject {
var Order:String?
var Date:String?
}
Use the below code in the view controller and you should be able to see content in your tableview
func getOrdersData() {
self.orderListArr.removeAll()
let ref = Database.database().reference().child(“users”).child(user).child("Orders")
ref.observe(.childAdded, with: { (snapshot) in
print(snapshot)
guard let dictionary = snapshot.value as? [String : AnyObject] else {
return
}
let orderObj = OrderModel()
orderObj.Order = dictionary[“Order”] as? String
orderObj.Date = dictionary[“Date”] as? String
self.orderListArr.append(orderObj)
self.tableView.delegate = self
self.tableView.dataSource = self
self.tableView.reloadData()
}, withCancel: nil)
}
func ListenForChildrenAdded() {
let registerToListenTo = "YourPathHere"
ref.child(registerToListenTo).observeSingleEvent(of: .value) { (snapshot) in
let initialChildren = snapshot.childrenCount
var incrementer = 0
ref.child(registerToListenTo).observe(.childAdded, with: { (snapshot) in
incrementer += 1
print("snapshot: \(snapshot.key) #\(incrementer)")
if incrementer == initialChildren {
print("-> All children found")
} else if incrementer > initialChildren {
print("-> Child Was Added - Run Some Code Here")
}
})
}}
In my iOS app, a user is able to add friends by searching for there unique username.
The user types the username in a textField and I have a textFieldDidChange notification which is fired every time the text changes.
Within that method I then call the Firebase method below to check if the username exists.
func searchFor(_ username: String) {
guard let uid = FIRAuth.auth()?.currentUser?.uid else {
return
}
let lowercaseUsername = username.lowercased()
let ref = FIRDatabase.database().reference()
ref.child(FirebaseDatabaseBranchNames.usernames.rawValue).child(lowercaseUsername).observeSingleEvent(of: .value, with: { [unowned self](snapshot) in
if snapshot.exists() {
if let usernameUid = snapshot.value as? String {
self.isUserAlreadyAFriend(ref, uid: uid, usernameUid: usernameUid)
}
} else {
// username doesn't exist
}
}, withCancel: nil)
}
How can I cancel this method, before performing it again?
When you attach a listener/observer, Firebase returns a handle for that observer. You can subsequently remove the listener/observer by calling ref.removeObserverWithHandle().
So assuming you want at most one observer, you can keep the reference and observer handle in a member field of you class and then use this code in the searchFor method:
if (self.searchHandle != nil) {
self.searchRef.removeObserverWithHandle(searchHandle)
}
self.searchRef = ref.child(FirebaseDatabaseBranchNames.usernames.rawValue).child(lowercaseUsername)
self.searchHandle = self.searchRef.observeSingleEvent(of: .value, with: { [unowned self](snapshot) in
if snapshot.exists() {
if let usernameUid = snapshot.value as? String {
self.isUserAlreadyAFriend(ref, uid: uid, usernameUid: usernameUid)
}
} else {
// username doesn't exist
}
}, withCancel: nil)
Be aware that you won't be saving data transfer with this though, as the most likely result is that the database client simply drops the data that it gets back from the server.
Better you add the "removeAllObservers()" after the observe single event block. It is working for me.
let ref = Database.database().reference().ref.child(XXXX).child(YYYYY)
ref.observeSingleEvent(of: .value, with: { (snapshot) in
}else{
}
}) { (error) in
print(error.localizedDescription)
}
ref.removeAllObservers()