I want to fetch the required app version number when the app starts. But I can't get the right key.
I have this code to fetch. I use observe single event because I use this method to check the required app version number. This method is only fired when the app starts to do the check.
func getVersion(completionHandler: #escaping (Result<Any?>) -> ()) {
let ref: DatabaseReference! = Database.database().reference().child("version").child("IOS")
ref?.observeSingleEvent(of: .value , with: { snapshot in
if snapshot.exists() {
let recent = snapshot.value as! NSDictionary
print(recent)
}
})
}
But it is returning old results? I have isPersistenceEnabled enabled at my Appdelegate.
This is the database structure:
I get no results when I use Database.database().reference().child("version").child("IOS").
snapshot.exists is false when I use that.
What I previously had was:
- version
|
IOS - 1.0
And i get result when I use Database.database().reference().child("version"), namely {iOS => 1.0}. I don't get it because it was my old structure.
The Firebase Realtime Database synchronizes and stores a local copy of the data for active listeners. In addition, you can keep specific locations in sync.
let scoresRef = Database.database().reference(withPath: "scores")
scoresRef.keepSynced(true)
The Firebase Realtime Database client automatically downloads the data at these locations and keeps it in sync even if the reference has no active listeners. You can turn synchronization back off with the following line of code.
scoresRef.keepSynced(false)
Haven't really tried it but it should work.
The observeSingleEvent method is used for data that doesn't really change, and as such it will fetch from the local cache if you have persistence enabled.
This Android solution (https://stackoverflow.com/a/40477280/883413) provides a workaround by using an alternate method, runTransactonBlock.
Transactions give an opportunity to edit any data before they are saved. Here, we can simply accept the data as correct as we are only interested in reading the latest values.
let ref: DatabaseReference! = Database.database().reference().child("version").child("IOS")
ref.runTransactionBlock({ (data) -> TransactionResult in
return TransactionResult.success(withValue: data)
}, andCompletionBlock: { (error, success, snapshot) in
if let snapshot = snapshot, snapshot.exists() {
if let recent = snapshot.value as? NSDictionary {
print(recent)
}
}
})
Related
I'm a little bit confused about addSnapshotListener and getDocuments. As I read in the firebase docs, getDocuments() is retrieving data once and addSnapshotListener is retrieving in real-time.
What I want to ask.
If I'm using getDocuments, and im changing some documents in the Firestore , it will not make the change in the app ? But if im using addSnapshotListener it will ?
I'm making an delivery app, which is the best to use to store pictures of food , descriptions etc.
This is what im using to retrieve labels and pictures from my app :
db.collection("labels").getDocuments { (snapshot, error) in
if let error = error {
print(error)
return
} else {
for document in snapshot!.documents {
let data = document.data()
let newEntry = Labels(
firstLabel: data["firstLabel"] as! String,
secondLabel: data["secondLabel"] as! String,
photoKey: data["photoKey"] as! String
)
self.labels
.append(newEntry)
}
}
DispatchQueue.main.async {
self.tableViewTest.reloadData()
}
getDocuments will return results one time, with the current Firestore data.
addSnapshotListener will return an initial result set (same as getDocuments) and get called any time that data changes.
If your data is modified in Firestore and you've used getDocuments, your app will not be notified of those changes. For example, in your delivery app, perhaps the item goes out-of-stock while the user is using it. Or, the price gets changed, the user is logged in from another device, etc -- many possibilities for why the data might change. By using a snapshot listener, you'd get notified if any of these changes happen.
However, if you're relatively confident you don't need updates to the data (like getting a user's address from the database, for example), you could opt to just use getDocuments.
I have an app that uses a snapshot listener to listen to data in a particular document. However, when a field in the document is updated, the data is read 7-10x over. Never read once, and never read the number of fields that are in my document, it always seems to be an arbitrary number. Also, when the read data prints out, it seems like every printout is the same except for a couple of fields that I'm not setting (like an array prints out "<__NSArrayM 0x282d9f240>" but the number changes on each print). As a result, minimal usage of my app is causing 5-10k reads. I'm trying to reduce the number of reads and I don't know exactly how, but the app has to read as data is updated, but my two questions are:
when I print the data from the listener, does each data print out signify a separate read operation? and
is there any way for the listener to be alerted of the update but wait to actually perform the read until the data is updated, then perform one read instead of multiple reads every time any field is updated? Or another strategy to reduce reads when multiple writes occur?
Not sure if this is helpful, but here is the code I'm using to perform the read...its pretty much the standard code from the firestore sdk:
env.db.collection(env.currentSessionCode!).document(K.FStore.docName).addSnapshotListener { [self] documentSnapshot, error in
guard let document = documentSnapshot else {
print("Error fetching snapshot: \(error!)")
return
}
guard let data = document.data() else {
print("Document data was empty.")
return
}
self.env.data1 = data[K.FStore.data1] as? String ?? "????"
self.env.data2 = data[K.FStore.data2] as? String ?? "????"
self.env.data3 = data[K.FStore.data3] as? [String] ?? ["????"]
self.env.data4 = data[K.FStore.data4] as? [String] ?? ["????"]
self.env.data5 = data[K.FStore.data5] as? Double ?? 0
self.env.data6 = data[K.FStore.data6] as? Double ?? 0
self.env.data7 = data[K.FStore.data7] as! Bool
self.env.data8 = data[K.FStore.data8] as! Bool
print("Current data: \(data)")
Update - For clarification, the way I have been updating my data to firebase is with a environment object, and using "didSet" when the new data is changed/updated in the environment to update it on firebase...I think this might be the root of the problem, as the function called on didSet runs 4-5 times each time it is called...
relevant code:
#Published var data1: String {
didSet {
postValuesToFB(fb: K.FStore.data1, string: data1)
}
}
func postValuesToFB(fb: String, string: String) {
guard let code = currentSessionCode else {
fatalError("Error - Connection Check - no value for current session code in Global Env")
}
let docRef = db.collection(code).document(K.FStore.docName)
docRef.getDocument { document, _ in
guard let document = document else {
return
}
if document.exists {
let session = self.db.collection(code).document(K.FStore.docName)
session.updateData([
fb: string,
K.FStore.dateLastAccessed: FieldValue.serverTimestamp(),
])
return
}
}
}
Based on your comments, it sounds as if you've written no code to remove a listener after it's been added. Based on this, it's relatively safe to assume that your code could be adding many listeners over time, and each one is getting called for each change.
You should take a moment to think about the architecture of your app and figure out when is the appropriate time to remove listeners when they're no longer needed. Usually this corresponds with the lifecycle of whatever component is responsible for display of the data from the query. Review the documentation for getting realtime updates, especially the section on detaching a listener. It's up to you to determine the right time to remove your listener, but you definitely don't want to "leak" a listener as you are now.
A common source of unexpected read charges for developers who are new to Firestore is the Firebase console itself. When that console displays Firestore content, you are charged for those read too. To ensure you measure the impact of your code correctly, test it with the Firebase console closed.
when I print the data from the listener, does each data print out signify a separate read operation?
Not really. You get charged for a document read, when the document is read on your behalf on the server. You are not charted for printing the same DocumentSnapshot multiple times.
is there any way for the listener to be alerted of the update but wait to actually perform the read until the data is updated
Nope. To know the document has changed, the server needs to read it. So that requires a charged read operation.
I am working with a Firebase Real Time database and I am having troubles with the execution of code at specific times. When I ask the database if there is a specific value in it, it executes the code to retrieve the data but then automatically continues unto the next line, not waiting for the retrieval of data. I am using this code to retrieve the data:
self.ref.child("Period \(periodListValue)").child("Students").child("\(studentName)").child("Novel Author").observeSingleEvent(of: .value) { (snapshot) in
self.CurrentAuthorTextField.text = (snapshot.value as! String)
}
The line of code right below this that is not associated with the database, executes right after this code above executes. Meaning I can't use any of the database information of the code right below the one shown above.
I am trying to explain this as best as I.
Any help?
Well, you have to use the completion handler for the following:-
func ifStudentPresent(studentName: String, completionHandler: #escaping ((_ exist : Bool) -> Void))
{
self.ref.child("Period \(periodListValue)").child("Students").child("\ .
(studentName)").child(studentName).observeSingleEvent(of: .value) { (snapshot) in
if snapshot.exists(){
completionHandler(true)
}else{
print("Student Don't exist")
completionHandler(false)
}
})
}
The reason you might be going through this problem is related to invalid database security rules. These can easily prevent you from retrieving your desired data and synchronizing your realtime database.
Let's assume you are trying to synchronize the ref database reference. You need to set the correct rules that allow reading from this database reference - something along the lines of ".read" = true".
[Warning] Please be careful with these database security rules. Incorrect rules can lead to drastically undesired behaviors, such as people illegally reading and/or writing from/into your database. A good video on how to set flawless security rules is The key to firebase security - Google I/O 2016
let dispatch = DispatchGroup.init()
dispatch.enter()
self.ref.child("Period \(periodListValue)").child("Students").child("\(studentName)").child("Novel Author").observeSingleEvent(of: .value) { (snapshot)
in
self.CurrentAuthorTextField.text = (snapshot.value as! String)
dispatch.leave()
}
dispatch.notify(queue: .main) {
//write code here, it will execute after database fetch
}
I have a query running to check .childAdded at a location in my database.
It works well when data is found, however, if there is not data at the location, it can't fire the query and therefore this does not allow me to use snapshot.exists because it doesn't even run the query.
This is my current code
let favouriteRef = self.databaseRef.child("users").child(userID!).child("Favourites")
// Code doesn't run past this line when no data at location
favouriteRef.queryOrderedByKey().observe(.childAdded, with: { (snapshot) in
let favouriteID = "\(snapshot.value!)"
let usersRef = self.databaseRef.child("users")
usersRef.observeSingleEvent(of: .value, with: { (users) in
for user in users.children {
let favCleaner = UserClass(snapshot: user as! DataSnapshot)
if favouriteID == favCleaner.uid {
tempFav.append(favCleaner)
}
}
self.hasFavourites = true
self.tableView.reloadData()
self.usersArray = tempFav
self.collectionView.reloadData()
})
})
I would like to find a way to receive a callback if the query doesn't run (no data at location)
Thanks.
If there is absolutely no data at the location, then obviously this event trigger is not sufficient for you to get the data because this event only gets triggered when something gets added.
So you have two options
Add another trigger of type .observeSingleEvent(of: .value, with: { (snapshot) in
// Get the values and write the relevant actions
}
Or you can update this event to type .observe(.value, with: {snapshot in // write the relevant code
}
Both approaches have their advantage and disadvantage.
First approach will need you to write more code while minimising the number of triggers from your database to your UI. In second approach, there will be more triggers to the UI but it can be fairly easy to code.
From what I can see, you are first trying to establish whether data exists in the favorite node of your database and then comparing it to another snapshot. So if the number of delete or update events are relatively small, my suggestion is to go for approach two.
My realtime database looks like this:
It contains only 1 child as you can see. I had 4 more children in RunningGames a few minutes before. I deleted them in the browser. When now calling this:
private lazy var runningGamesRef: FIRDatabaseReference = FIRDatabase.database().reference().child("RunningGames")
self.runningGamesRef.observeSingleEvent(of: .value, with: { (snapshot) -> Void in
for gameSnap in snapshot.children {
let id = (gameSnap as! FIRDataSnapshot).key
print(id)
}
})
It still prints those games I deleted in the browser. Calling runningGameRef!.removeValues() in my app does deletes it in the browser and on the iPhone (the print(id) is fixed). I have this error on multiple observeSingleEvent functions on different children, not only children of RunningGames. What would cause this annoying error?
Some children in RunningGames also have children, but they do auto remove themselves in the app. However, these values are also still visible when calling observeSingleEvent.
It's probably your local cache that's still holding the outdated info. This often happens when you're manipulating data from multiple sources.
I would try using observe instead of observeSingleEvent. I know it's a bit odd (and not really what you want if you only want to load the data once) but that should keep your info up to date.
Maybe by doing this you could fetch the info just once.
var handle: UInt = 0
handle = ref.observe(.value, with: { snapshot in
for gameSnap in snapshot.children {
let id = (gameSnap as! FIRDataSnapshot).key
print(id)
}
ref.removeObserver(withHandle: handle)
})
Source of the code (Frank van Puffelen)