I'm trying to run a Firebase Transaction under a suspended function in Kotlin and i see no documentation about it.
I'm using
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-play-services:1.5.2'
for coroutines with firebase (eg: setValue(*).await() ) but there seems to be no await function for runTransaction(*)
override suspend fun modifyProductStock(
product: ProductModel,
valueToModify: Long,
replace: Boolean
) {
CoroutineScope(Dispatchers.Main).launch {
val restaurantId = authRepository.restaurantId.value ?: throw Exception("No restaurant!")
val productId = product.id ?: throw Exception("No Product ID!")
val reference = FirebaseDatabase.getInstance().getReference("database/$restaurantId").child("products")
if (replace) {
reference.child(productId).child("stock").setValue(valueToModify).await()
} else {
reference.child(productId).child("stock")
.runTransaction(object : Transaction.Handler {
override fun doTransaction(p0: MutableData): Transaction.Result {
//any operation
return Transaction.success(p0)
}
override fun onComplete(p0: DatabaseError?, p1: Boolean, p2: DataSnapshot?) {
}
})
}
}
}
You could wrap it in suspendCoroutine:
val result: DataSnapshot? = suspendCoroutine { c ->
reference.child(productId).child("stock")
.runTransaction(object : Transaction.Handler {
override fun doTransaction(p0: MutableData): Transaction.Result {
//any operation
return Transaction.success(p0)
}
override fun onComplete(error: DatabaseError?, p1: Boolean, snapshot: DataSnapshot?) {
c.resume(snapshot)
}
})
}
suspendCoroutine
Obtains the current continuation instance inside suspend functions and suspends the currently running coroutine.
In this function both Continuation.resume and Continuation.resumeWithException can be used either synchronously in the same stack-frame where the suspension function is run or asynchronously later in the same thread or from a different thread of execution.
Given that the Kotlin example in the Firebase documentation on transactions uses the same callback style that you have, it seems indeed that there is no specific support for co-routines there.
It might be worth posting an issue on the Android SDK repo to get it added, or hear why it wasn't added.
Related
firebase method is working on worker thread automatically. but I have used coroutine and callbackflow to implement firebase listener code synchronously or get return from the listener.
below is my code that I explained
coroutine await with firebase for one shot
override suspend fun checkNickName(nickName: String): Results<Int> {
lateinit var result : Results<Int>
fireStore.collection("database")
.document("user")
.get()
.addOnCompleteListener { document ->
if (document.isSuccessful) {
val list = document.result.data?.get("nickNameList") as List<String>
if (list.contains(nickName))
result = Results.Exist(1)
else
result = Results.No(0)
//document.getResult().get("nickNameList")
}
else {
}
}.await()
return result
}
callbackflow with firebase listener
override fun getOwnUser(): Flow<UserEntity> = callbackFlow{
val document = fireStore.collection("database/user/userList/")
.document("test!!!!!")
val subscription = document.addSnapshotListener { snapshot,_ ->
if (snapshot!!.exists()) {
val ownUser = snapshot.toObject<UserEntity>()
if (ownUser != null) {
trySend(ownUser)
}
}
}
awaitClose { subscription.remove() }
}
so I really wonder these way is good or bad practice and its reason
Do not combine addOnCompleteListener with coroutines await(). There is no guarantee that the listener gets called before or after await(), so it is possible the code in the listener won't be called until after the whole suspend function returns. Also, one of the major reasons to use coroutines in the first place is to avoid using callbacks. So your first function should look like:
override suspend fun checkNickName(nickName: String): Results<Int> {
try {
val userList = fireStore.collection("database")
.document("user")
.get()
.await()
.get("nickNameList") as List<String>
return if (userList.contains(nickName)) Results.Exist(1) else Results.No(0)
} catch (e: Exception) {
// return a failure result here
}
}
Your use of callbackFlow looks fine, except you should add a buffer() call to the flow you're returning so you can specify how to handle backpressure. However, it's possible you will want to handle that downstream instead.
override fun getOwnUser(): Flow<UserEntity> = callbackFlow {
//...
}.buffer(/* Customize backpressure behavior here */)
thank you for taking your time to read my problem.
Im currently using Firebase Firestore to retrieve a list of objects that I which to display to the UI, im trying to use a suspend function to fold the accumulative values of a sequence of calls from the Firestore server, but at the moment im unable to pass the result value outside the scope of the coroutine.
This is my fold function:
suspend fun getFormattedList(): FirestoreState {
return foldFunctions(FirestoreModel(""), ::getMatchesFromBackend, ...., ....)
}
This is my custom fold function:
suspend fun foldFunctions(model: FirestoreModel,
vararg functions: suspend (FirestoreModel, SuccessData) -> FirestoreState): FirestoreState {
val successData: SuccessData = functions.fold(SuccessData()) { updatedSuccessData, function ->
val status = function(model, updatedSuccessData)
if (status !is FirestoreState.Continue) {
return status
}
updatedSuccessData <--- I managed to retrieve the list of values correctly here
}
val successModel = SuccessData()
successData.matchList?.let { successModel.matchList = it }
successData.usermatchList?.let { successModel.usermatchList = it }
successData.formattedList?.let { successModel.formattedList = it }
return FirestoreState.Success(successModel) <--- I cant event get to this line with debugger on
}
This is my first function (which is working fine)
suspend fun getMatchesFromBackend(model: FirestoreModel, successData: SuccessData): FirestoreState {
return try {
val querySnapshot: QuerySnapshot? = db.collection("matches").get().await()
querySnapshot?.toObjects(Match::class.java).let { list ->
val matchList = mutableListOf<Match>()
list?.let {
for (document in it) {
matchList.add(Match(document.away_score,
document.away_team,
document.date,
document.home_score,
document.home_team,
document.match_id,
document.matchpoints,
document.played,
document.round,
document.tournament))
}
successData.matchList = matchList <--- where list gets stored
}
}
FirestoreState.Continue
} catch (e : Exception){
when (e) {
is RuntimeException -> FirestoreState.MatchesFailure
is ConnectException -> FirestoreState.MatchesFailure
is CancellationException -> FirestoreState.MatchesFailure
else -> FirestoreState.MatchesFailure
}
}
}
My hypothesis is that the suspen fun get cancelled and the continuation of the scope gets blocked, I have tried to use runBlocking { } without vail. If someone has an idea of how to circumvent this issue I'd be very gratefull.
I am trying to understand which is the best way to have an asynchronous job fired at a scheduled rate in Kotlin, while the application is normally running it's normal tasks. Let's say I have a simple application that only prints out "..." every second, but every 5 seconds I want another job / thread / coroutine (which ever suits best) to print "you have a message!". For the async job I have a class NotificationProducer and it looks like this.
class NotificationProducer {
fun produce() {
println("You have a message!")
}
}
Then, my main method looks like this.
while (true) {
println("...")
sleep(1000)
}
Should I use GlobalScope.async, Timer().schedule(...) or some Quartz job to achieve what I want? Any advice is highly appreciated. The point is that notification must come from another class (e.g. NotificationProducer)
If I correctly understand the issue, using Kotlin Coroutines you can implement it as the following:
class Presenter : CoroutineScope { // implement CoroutineScope to create local scope
private var job: Job = Job()
override val coroutineContext: CoroutineContext
get() = Dispatchers.Default + job
// this method will help to stop execution of a coroutine.
// Call it to cancel coroutine and to break the while loop defined in the coroutine below
fun cancel() {
job.cancel()
}
fun schedule() = launch { // launching the coroutine
var seconds = 1
val producer = NotificationProducer()
while (true) {
println("...")
delay(1000)
if (seconds++ == 5) {
producer.produce()
seconds = 1
}
}
}
}
Then you can use an instance of the Presenter class to launch the coroutine and stop it:
val presenter = Presenter()
presenter.schedule() // calling `schedule()` function launches the coroutine
//...
presenter.cancel() // cancel the coroutine when you need
For simple scheduling requirements, you can consider using coroutines:
class NotificationProducerScheduler(val service: NotificationProducer, val interval: Long, val initialDelay: Long?) :
CoroutineScope {
private val job = Job()
private val singleThreadExecutor = Executors.newSingleThreadExecutor()
override val coroutineContext: CoroutineContext
get() = job + singleThreadExecutor.asCoroutineDispatcher()
fun stop() {
job.cancel()
singleThreadExecutor.shutdown()
}
fun start() = launch {
initialDelay?.let {
delay(it)
}
while (isActive) {
service.produce()
delay(interval)
}
println("coroutine done")
}
}
Otherwise, the Java concurrency API is pretty solid too:
class NotificationProducerSchedulerJavaScheduler(
val service: NotificationProducer,
val interval: Long,
val initialDelay: Long = 0
) {
private val scheduler = Executors.newScheduledThreadPool(1)
private val task = Runnable { service.produce() }
fun stop() {
scheduler.shutdown()
}
fun start() {
scheduler.scheduleWithFixedDelay(task, initialDelay, interval, TimeUnit.MILLISECONDS)
}
}
This function will run a task in the background while proceeding with a "main" task that controls the lifecycle of the background job. Below is an example of usage.
/**
* Runs a task in the background in IO while the op proceeds.
* The job is canceled when op returns.
* This is useful for updating caches and the like.
*/
suspend fun withBackgroundTask(task: suspend () -> Unit, op: suspend () -> Unit) {
val job = CoroutineScope(Dispatchers.IO).launch { task() }
try {
op()
} finally {
job.cancel()
}
}
/**
* Updates the cache in a background task while op runs.
*/
suspend fun withCache(cache: Cache<*>, op: suspend () -> Unit) {
suspend fun cacheUpdate() {
cache.fetchInternal()
while (true) {
delay(cache.cycle)
cache.fetchInternal()
}
}
withBackgroundTask(::cacheUpdate, op)
}
I'm trying to optimise the performances in my app and I noticed that I do not remove Firestore listeners from my repository.
My repository has a number of functions that return a LiveData, that is then observed via Transformations from ViewModels and then the views.
One-time operations work absolutely fine (upload, delete etc.) but permanent listeners don't get garbage collected when the activity finishes.
Right now the function inside the repository looks like this:
// [...]
class Repository {
// [...]
fun retrieveCode() {
val observable = MutableLiveData<Code>()
val reference =
FirebaseFirestore.getInstance().collection(/**/).document(/**/)
reference
.addSnapshotListener { snapshot, exception ->
if(exception != null) {
observable.value = null
}
if(snapshot != null {
observable.value = snapshot.//[convert to object]
}
}
return observable
}
}
I found a workaround which is to create a custom LiveData object that handles the listener removal when it becomes inactive, like this:
class CodeLiveData(private val reference: DocumentReference):
LiveData<Code>(), EventListener<DocumentSnapshot>{
private var registration: ListenerRegistration? = null
override fun onEvent(snapshot: DocumentSnapshot?,
exception: FirebaseFirestoreException?) {
if(exception != null) {
this.value = null
}
if(snapshot != null) {
this.value = snapshot.//[convert to object]
}
}
override fun onActive() {
super.onActive()
registration = reference.addSnapshotListener(this)
}
override fun onInactive() {
super.onInactive()
registration?.remove()
}
}
Is there a way to solve this problem without creating a custom class, but rather by improving a function similar to the first example?
Thanks,
Emilio
There are two ways in which you can achieve this. The first one would be to stop listening for changes and this can be done in your onStop() function by calling remove() function on your ListenerRegistration object like this:
if (registration != null) {
registration.remove();
}
The approach would be to you pass your activity as the first argument in the addSnapshotListener() function, so Firestore can clean up the listeners automatically when the activity is stopped.
var registration = dataDocumentReference
.addSnapshotListener(yourActivity, listener)
I'm not sure of the best approach for handling scoping of "this" in TypeScript.
Here's an example of a common pattern in the code I am converting over to TypeScript:
class DemonstrateScopingProblems {
private status = "blah";
public run() {
alert(this.status);
}
}
var thisTest = new DemonstrateScopingProblems();
// works as expected, displays "blah":
thisTest.run();
// doesn't work; this is scoped to be the document so this.status is undefined:
$(document).ready(thisTest.run);
Now, I could change the call to...
$(document).ready(thisTest.run.bind(thisTest));
...which does work. But it's kinda horrible. It means that code can all compile and work fine in some circumstances, but if we forget to bind the scope it will break.
I would like a way to do it within the class, so that when using the class we don't need to worry about what "this" is scoped to.
Any suggestions?
Update
Another approach that works is using the fat arrow:
class DemonstrateScopingProblems {
private status = "blah";
public run = () => {
alert(this.status);
}
}
Is that a valid approach?
You have a few options here, each with its own trade-offs. Unfortunately there is no obvious best solution and it will really depend on the application.
Automatic Class Binding
As shown in your question:
class DemonstrateScopingProblems {
private status = "blah";
public run = () => {
alert(this.status);
}
}
Good/bad: This creates an additional closure per method per instance of your class. If this method is usually only used in regular method calls, this is overkill. However, if it's used a lot in callback positions, it's more efficient for the class instance to capture the this context instead of each call site creating a new closure upon invoke.
Good: Impossible for external callers to forget to handle this context
Good: Typesafe in TypeScript
Good: No extra work if the function has parameters
Bad: Derived classes can't call base class methods written this way using super.
Bad: The exact semantics of which methods are "pre-bound" and which aren't create an additional non-typesafe contract between your class and its consumers.
Function.bind
Also as shown:
$(document).ready(thisTest.run.bind(thisTest));
Good/bad: Opposite memory/performance trade-off compared to the first method
Good: No extra work if the function has parameters
Bad: In TypeScript, this currently has no type safety
Bad: Only available in ECMAScript 5, if that matters to you
Bad: You have to type the instance name twice
Fat arrow
In TypeScript (shown here with some dummy parameters for explanatory reasons):
$(document).ready((n, m) => thisTest.run(n, m));
Good/bad: Opposite memory/performance trade-off compared to the first method
Good: In TypeScript, this has 100% type safety
Good: Works in ECMAScript 3
Good: You only have to type the instance name once
Bad: You'll have to type the parameters twice
Bad: Doesn't work with variadic parameters
Another solution that requires some initial setup but pays off with its invincibly light, literally one-word syntax is using Method Decorators to JIT-bind methods through getters.
I've created a repo on GitHub to showcase an implementation of this idea (it's a bit lengthy to fit into an answer with its 40 lines of code, including comments), that you would use as simply as:
class DemonstrateScopingProblems {
private status = "blah";
#bound public run() {
alert(this.status);
}
}
I haven't seen this mentioned anywhere yet, but it works flawlessly. Also, there is no notable downside to this approach: the implementation of this decorator -- including some type-checking for runtime type-safety -- is trivial and straightforward, and comes with essentially zero overhead after the initial method call.
The essential part is defining the following getter on the class prototype, which is executed immediately before the first call:
get: function () {
// Create bound override on object instance. This will hide the original method on the prototype, and instead yield a bound version from the
// instance itself. The original method will no longer be accessible. Inside a getter, 'this' will refer to the instance.
var instance = this;
Object.defineProperty(instance, propKey.toString(), {
value: function () {
// This is effectively a lightweight bind() that skips many (here unnecessary) checks found in native implementations.
return originalMethod.apply(instance, arguments);
}
});
// The first invocation (per instance) will return the bound method from here. Subsequent calls will never reach this point, due to the way
// JavaScript runtimes look up properties on objects; the bound method, defined on the instance, will effectively hide it.
return instance[propKey];
}
Full source
The idea can be also taken one step further, by doing this in a class decorator instead, iterating over methods and defining the above property descriptor for each of them in one pass.
Necromancing.
There's an obvious simple solution that doesn't require arrow-functions (arrow-functions are 30% slower), or JIT-methods through getters.
That solution is to bind the this-context in the constructor.
class DemonstrateScopingProblems
{
constructor()
{
this.run = this.run.bind(this);
}
private status = "blah";
public run() {
alert(this.status);
}
}
You can write an autobind method to automatically bind all functions in the constructor of the class:
class DemonstrateScopingProblems
{
constructor()
{
this.autoBind(this);
}
[...]
}
export function autoBind(self)
{
for (const key of Object.getOwnPropertyNames(self.constructor.prototype))
{
const val = self[key];
if (key !== 'constructor' && typeof val === 'function')
{
// console.log(key);
self[key] = val.bind(self);
} // End if (key !== 'constructor' && typeof val === 'function')
} // Next key
return self;
} // End Function autoBind
Note that if you don't put the autobind-function into the same class as a member function, it's just autoBind(this); and not this.autoBind(this);
And also, the above autoBind function is dumbed down, to show the principle.
If you want this to work reliably, you need to test if the function is a getter/setter of a property as well, because otherwise - boom - if your class contains properties, that is.
Like this:
export function autoBind(self)
{
for (const key of Object.getOwnPropertyNames(self.constructor.prototype))
{
if (key !== 'constructor')
{
// console.log(key);
let desc = Object.getOwnPropertyDescriptor(self.constructor.prototype, key);
if (desc != null)
{
if (!desc.configurable) {
console.log("AUTOBIND-WARNING: Property \"" + key + "\" not configurable ! (" + self.constructor.name + ")");
continue;
}
let g = desc.get != null;
let s = desc.set != null;
if (g || s)
{
var newGetter = null;
var newSetter = null;
if (g)
newGetter = desc.get.bind(self);
if (s)
newSetter = desc.set.bind(self);
if (newGetter != null && newSetter == null) {
Object.defineProperty(self, key, {
get: newGetter,
enumerable: desc.enumerable,
configurable: desc.configurable
});
}
else if (newSetter != null && newGetter == null) {
Object.defineProperty(self, key, {
set: newSetter,
enumerable: desc.enumerable,
configurable: desc.configurable
});
}
else {
Object.defineProperty(self, key, {
get: newGetter,
set: newSetter,
enumerable: desc.enumerable,
configurable: desc.configurable
});
}
continue; // if it's a property, it can't be a function
} // End if (g || s)
} // End if (desc != null)
if (typeof (self[key]) === 'function')
{
let val = self[key];
self[key] = val.bind(self);
} // End if (typeof (self[key]) === 'function')
} // End if (key !== 'constructor')
} // Next key
return self;
} // End Function autoBind
In your code, have you tried just changing the last line as follows?
$(document).ready(() => thisTest.run());