In this application, each user has a counter for "votes" but it only works when the same user votes, when another user tries to do a FIRTransaction in that reference it returns nil. The rules are set to any user.
When I need that user2 updates the user1 "votes" value it doesn't reads that key value to perform the transaction block, so it returns nil.
votesCountRef = ref.child("user1").child("votes")
votesCountRef.runTransactionBlock( { (currentData) -> FIRTransactionResult in
let value = currentData.value! as! Int
currentData.value = value + 1
return FIRTransactionResult.successWithValue(currentData)
})
result:
Received votes actual value: Optional()
Could not cast value of type 'NSNull' (0x110684600) to 'NSNumber' (0x10fce92a0).
But when original user runs this it works successfully.
Json tree for user1:
{
"userUID" : "user1",
"votes" : 2
}
Database rules:
{
"rules": {
".read": "auth != null",
".write": "auth != null"
}
}
Thanks to #Frank I could manage it like this:
ownerReceivedVotesCountRef.runTransactionBlock( { (currentData) -> FIRTransactionResult in
let value = currentData.value as? Int ?? 0
currentData.value! = (value as Int) + 1
return FIRTransactionResult.successWithValue(currentData)
})
A transaction handler is initially run with the client's best guess fo rthe current value. Quite often that will be nil, so your code has to handle that.
From the Firebase documentation:
Note: Because runTransactionBlock:andCompletionBlock: is called multiple times, it must be able to handle nil data. Even if there is existing data in your remote database, it may not be locally cached when the transaction function is run, resulting in nil for the initial value.
Something like this should work for your case:
let value = currentData.value as? Int ?? 0
Related
I've spent days researching this including various answers like: Firebase Firestore: Append/Remove items from document array and my previous question at: Removing an array item from Firestore
but can't work out how to actually get this working. Turns out the issue is when there is a date property in the object as shown below:
I have two structs:
struct TestList : Codable {
var title : String
var color: String
var number: Int
var date: Date
var asDict: [String: Any] {
return ["title" : self.title,
"color" : self.color,
"number" : self.number,
"date" : self.date]
}
}
struct TestGroup: Codable {
var items: [TestList]
}
I am able to add data using FieldValue.arrayUnion:
#objc func addAdditionalArray() {
let testList = TestList(title: "Testing", color: "blue", number: Int.random(in: 1..<999), date: Date())
let docRef = FirestoreReferenceManager.simTest.document("def")
docRef.updateData([
"items" : FieldValue.arrayUnion([["title":testList.title,
"color":testList.color,
"number":testList.number,
"date": testList.date]])
])
}
The above works as reflected in the Firestore dashboard:
But if I try and remove one of the items in the array, it just doesn't work.
#objc func deleteArray() {
let docRef = FirestoreReferenceManager.simTest.document("def")
docRef.getDocument { (document, error) in
do {
let retrievedTestGroup = try document?.data(as: TestGroup.self)
let retrievedTestItem = retrievedTestGroup?.items[1]
guard let itemToRemove = retrievedTestItem else { return }
docRef.updateData([
"items" : FieldValue.arrayRemove([itemToRemove.asDict])
]) { error in
if let error = error {
print("error: \(error)")
} else {
print("successfully deleted")
}
}
} catch {
}
}
}
I have printed the itemToRemove to the log to check that it is correct and it is. But it just doesn't remove it from Firestore. There is no error returned, yet the "successfully deleted" is logged.
I've tried different variations and this code works as long as I don't have a date property in the struct/object. The moment I add a date field, it breaks and stops working. Any ideas on what I'm doing wrong here?
Please note: I've tried passing in the field values as above in FieldValue.arrayUnion as well as the object as per FieldValue.arrayRemove and the same issue persists regardless of which method I use.
The problem is, as you noted, the Date field. And it's a problem because Firestore does not preserve the native Date object when it's stored in the database--they are converted into date objects native to Firestore. And the go-between these two data types is a token system. For example, when you write a date to Firestore from a Swift client, you actually send the database a token which is then redeemed by the server when it arrives which then creates the Firestore date object in the database. Conversely, when you read a date from Firestore on a Swift client, you actually receive a token which is then redeemed by the client which you then can convert into a Swift Date object. Therefore, the definition of "now" is not the same on the client as it is on the server, there is a discrepancy.
That said, in order to remove a specific item from a Firestore array, you must recreate that exact item to give to FieldValue.arrayRemove(), which as you can now imagine is tricky with dates. Unlike Swift, you cannot remove items from Firestore arrays by index. Therefore, if you want to keep your data architecture as is (because there is a workaround I will explain below), the safest way is to get the item itself from the server and pass that into FieldValue.arrayRemove(). You can do this with a regular read and then execute the remove in the completion handler or you can perform it atomically (safer) in a transaction.
let db = Firestore.firestore()
db.runTransaction { (trans, errorPointer) -> Any? in
let doc: DocumentSnapshot
let docRef = db.document("test/def")
// get the document
do {
try doc = trans.getDocument(docRef)
} catch let error as NSError {
errorPointer?.pointee = error
return nil
}
// get the items from the document
if let items = doc.get("items") as? [[String: Any]] {
// find the element to delete
if let toDelete = items.first(where: { (element) -> Bool in
// the predicate for finding the element
if let number = element["number"] as? Int,
number == 385 {
return true
} else {
return false
}
}) {
// element found, remove it
docRef.updateData([
"items": FieldValue.arrayRemove([toDelete])
])
}
} else {
// array itself not found
print("items not found")
}
return nil // you can return things out of transactions but not needed here so return nil
} completion: { (_, error) in
if let error = error {
print(error)
} else {
print("transaction done")
}
}
The workaround I mentioned earlier is to bypass the token system altogether. And the simplest way to do that is to express time as an integer, using the Unix timestamp. This way, the date is stored as an integer in the database which is almost how you'd expect it to be stored anyway. This makes locating array elements that contain dates simpler because time on the client is now equal to time on the server. This is not the case with tokens because the actual date that is stored in the database, for example, is when the token is redeemed and not when it was created.
You can extend Date to conveniently convert dates to timestamps and extend Int to conveniently convert timestamps to dates:
typealias UnixTimestamp = Int
extension Date {
var unixTimestamp: UnixTimestamp {
return UnixTimestamp(self.timeIntervalSince1970 * 1_000) // millisecond precision
}
}
extension UnixTimestamp {
var dateObject: Date {
return Date(timeIntervalSince1970: TimeInterval(self / 1_000)) // must take a millisecond-precision unix timestamp
}
}
One last thing is that in my example, I located the element to delete by its number field (I used your data), which I assumed to be a unique identifier. I don't know the nature of these elements and how they are uniquely identified so consider the filter predicate in my code to be purely an assumption.
I am currently using Google Firestore to host a database, allowing users to add in a series of products. Whenever a user adds their first product, this is added fine. However, once the user adds a second product, the initial product data is always overwritten as my method which sends the data to the Database is hardcoded as "product1". I am trying to create a function which reads all of the fields in my database beginning with "product" to try and find the first "product" + "integer" which isn't currently in the database, and to use this name and add the data. I am currently trying to increment the value afterward the "product" name e.g. ("product1", "product2" etc.) and then once it finds a "product(Int)" which is equal to nil (indicating that the field is empty/doesn't exist yet), then the data can be added using this "product(Int)" value. In the example image below, the database currently has "product1" populated with data, so when a user adds another product, the function is run, "product1" would return != nil, so the function would then increment and try "product2", which = nil, then the integer value (in this case, 2) is assigned to valueIncrement and then concatenated to the "products" name, resulting in the product being posted to the database under the field name - "product2"
Database Structure Example
I am using the following code to achieve this.
func incrementNumber() {
db.collection("users").getDocuments { (snapshot, error) in
if data["product"] as? String == nil {
(products) = ["product1"]
return
} else {
try (products)+=1
if (products) != nil {
let valueIncrement = products.product as! String
}
let productDict =
(productname,producturl,pricefield,proddesc,timeleft)
let combinedString = "\(productDict)"
document.reference.updateData([
"product \(valueIncrement)":(combinedString)
])
}
}
}
However I am getting the following error for curly brace (leaving me unable to test whether my function is working as intended) here - getDocuments {.
Invalid conversion from throwing function of type '(QuerySnapshot?, Error?) throws -> Void' to non-throwing function type '(QuerySnapshot?, Error?) -> Void'
Why am I getting this error?
I have been trying to implement Chris’ answer here: Can I make Firebase use a username login process? for the Facebook login but I can’t seem to get my head around it.
So far I’ve tried to set conditions on the textField but as Firebase observer works asynchronously, the conditions to check if the username exists in the database won’t work.
let usernameString = usernameTextField.text
let uid = FIRAuth.auth()?.currentUser?.uid
ref.runTransactionBlock({ (currentData: FIRMutableData) -> FIRTransactionResult in
if var post = currentData.value as? [String : AnyObject], let uid = FIRAuth.auth()?.currentUser?.uid {
let usernamesDictionary = post["usernames"] as! NSDictionary
for (key, _) in usernamesDictionary {
if key as? String == usernameString {
print("username not available: \(key)")
}
else if usernameString == "" {
print("Uh oh! Looks like you haven't set a username yet.")
}
else if key as? String != usernameString {
print("username available: \(key)")
print("All set to go!")
let setValue: NSDictionary = [usernameString!: uid]
post["usernames"] = setValue
currentData.value = post
}
}
return FIRTransactionResult.successWithValue(currentData)
}
return FIRTransactionResult.successWithValue(currentData)
}
Then I tried creating /usernames/ node in the database and set up rules as:
{
"rules": {
"usernames": {
".read": "auth != null",
".write": "newData.val() === auth.uid && !data.exists()"
}
}
}
Now that won’t let me set any username to the database. I get confused in creating rules but my whole point is that I need a sign up flow with the username data that’s unique for each user in the database.
While trying every answer I found in related posts, what worked for me the easy way i.e. without making Firebase rules play a part in it or creating a separate usernames node in the database was to not put an if/else condition inside the Firebase observer but instead to use the exists() method of FIRDataSnapshot.
Now here’s the trick, while I did try only the exists() method with a simple observer but that did not help me. What I did was first query usernames in order, then match the username with queryEqualToValue to filter the query:
refUsers.queryOrderedByChild("username").queryEqualToValue(usernameString).observeSingleEventOfType(.Value , withBlock: {
snapshot in
if !snapshot.exists() {
if usernameString == "" {
self.signupErrorAlert("Uh oh!", message: "Looks like you haven't set a username yet.")
}
else {
// Update database with a unique username.
}
}
else {
self.signupErrorAlert("Uh oh!", message: "\(usernameString!) is not available. Try another username.")
}
}) { error in
print(error.localizedDescription)
}
}
This is the first time out of most of the answers here that worked for me. But for now, I don’t know if this would scale. Post your experiences and best practices. They’ll be appreciated.
I have this function trying to run transaction to update Firebase value:
if opponentPoints < self.points {
print("the host won")
refPoints.runTransactionBlock({ (currentData:FIRMutableData) -> FIRTransactionResult in
print("currentData", currentData.value!)
if var pointsToUpdate = currentData.value as? [String : Any] {
var pointsUp = pointsToUpdate["points"] as! Int
pointsUp += 3
pointsToUpdate["points"] = pointsUp
currentData.value = pointsToUpdate
return FIRTransactionResult.success(withValue: currentData)
}
return FIRTransactionResult.success(withValue: currentData)
})
and I have this structure:
users
uid
points
name
etc.
The problem is that when I try to print currentData, I get null as result.
What am I doing wrong?
When you start a transaction, you transaction handlers is immediately invoked with the client's best guess for the current value of the data. This will most often be null.
The Firebase client then send the best guess (null) and your value to the server. The server checks, realizes that the current value is wrong and rejects the change. In that rejection, it then tells the client the current value of the location.
The Firebase client then invokes your transaction handler again, but now with the new best guess to the current value.
Long story short: your transaction handler needs to be prepared to receive null as the current value.
I've looked over hours of code and notes and I'm struggling to find any documentation that would help me with upvoting and downvoting an object in a swift app with firebase.
I have a gallery of photos and I'm looking to add an instagram style upvote to images. The user has already logged with firebase auth so I have their user ID.
I'm just struggling to figure the method and what rules need to be set in firebase.
Any help would be awesome.
I will describe how I implemented such a feature in social networking app Impether using Swift and Firebase.
Since upvoting and downvoting is analogous, I will describe upvoting only.
The general idea is to store a upvotes counter directly in the node corresponding to an image data the counter is related to and update the counter value using transactional writes in order to avoid inconsistencies in the data.
For example, let's assume that you store a single image data at path /images/$imageId/, where $imageId is an unique id used to identify a particular image - it can be generated for example by a function childByAutoId included in Firebase for iOS. Then an object corresponding to a single photo at that node looks like:
$imageId: {
'url': 'http://static.example.com/images/$imageId.jpg',
'caption': 'Some caption',
'author_username': 'foobarbaz'
}
What we want to do is to add an upvote counter to this node, so it becomes:
$imageId: {
'url': 'http://static.example.com/images/$imageId.jpg',
'caption': 'Some caption',
'author_username': 'foobarbaz',
'upvotes': 12,
}
When you are creating a new image (probably when an user uploads it), then you may want to initialize the upvote counter value with 0 or some other constant depending on what are you want to achieve.
When it comes to updating a particular upvotes counter, you want to use transactions in order to avoid inconsistencies in its value (this can occur when multiple clients want to update a counter at the same time).
Fortunately, handling transactional writes in Firebase and Swift is super easy:
func upvote(imageId: String,
success successBlock: (Int) -> Void,
error errorBlock: () -> Void) {
let ref = Firebase(url: "https://YOUR-FIREBASE-URL.firebaseio.com/images")
.childByAppendingPath(imageId)
.childByAppendingPath("upvotes")
ref.runTransactionBlock({
(currentData: FMutableData!) in
//value of the counter before an update
var value = currentData.value as? Int
//checking for nil data is very important when using
//transactional writes
if value == nil {
value = 0
}
//actual update
currentData.value = value! + 1
return FTransactionResult.successWithValue(currentData)
}, andCompletionBlock: {
error, commited, snap in
//if the transaction was commited, i.e. the data
//under snap variable has the value of the counter after
//updates are done
if commited {
let upvotes = snap.value as! Int
//call success callback function if you want
successBlock(upvotes)
} else {
//call error callback function if you want
errorBlock()
}
})
}
The above snipped is actually almost exactly the code we use in production. I hope it helps you :)
I was very surprised, but this code from original docs works like a charm. There is one disadvantage with it: the json grows pretty big if there are a lot of likes.
FirebaseService.shared.databaseReference
.child("items")
.child(itemID!)
.runTransactionBlock({ (currentData: MutableData) -> TransactionResult in
if var item = currentData.value as? [String : AnyObject] {
let uid = SharedUser.current!.id
var usersLikedIdsArray = item["liked_who"] as? [String : Bool] ?? [:]
var likesCount = item["likes"] as? Int ?? 0
if usersLikedIdsArray[uid] == nil {
likesCount += 1
usersLikedIdsArray[uid] = true
self.setImage(self.activeImage!, for: .normal)
self.updateClosure?(true)
} else {
likesCount -= 1
usersLikedIdsArray.removeValue(forKey: uid)
self.setImage(self.unactiveImage!, for: .normal)
self.updateClosure?(false)
}
item["liked_who"] = usersLikedIdsArray as AnyObject?
item["likes"] = likesCount as AnyObject?
currentData.value = item
return TransactionResult.success(withValue: currentData)
}
return TransactionResult.success(withValue: currentData)
}) { (error, committed, snapshot) in
if let error = error {
self.owner?.show(error: error)
}
}
Not a Swift fella myself (pun!) but I think this stackoverflow question has most of your answers.
Then you would simply use a couple of if statements to return the correct value from the transaction based on whether you want to up vote or down vote.