I'm having trouble how to design the architecture of my Android App. I'm using the repository pattern, however, how can I observe a Room entity when the return type is a Dataclass with Success/Failure within a Flow and using a uiState Dataclass. Let me elaborate more with an image:
In my viewmodel, I have the repository injected with Hilt. So I can call _myRepo.getData().
The repository executes a network call (retrofit) and awaits the result.
The server returns a JSON with the data requested.
With a serializer, I convert the JSON to a list of DTOs. These DTO's are mapped to Entities and inserted in the Room Database.
Now comes the confusing part.
If my ResultType dataclass is:
sealed class ResultType<T> (val data : T? = null, val message : String? = null) {
class Success<T>(data: T?) : ResultType<T>(data)
class Error<T>(message: String?, data: T? = null) : ResultType<T>(data, message)
class Loading<T>(val isLoading: Boolean = true) : ResultType<T>(null)
}
In my repository, the function getData() looks like:
suspend fun getData() : Flow<ResultType<List<UserDataClass>>> = flow {
try {
emit(ResultType.Loading(true))
val mylist = _api.getUsers(mapparameters).map { it.toUserEntity() }
_db.userDao.delete()
_db.userDao.insertAll(mylist)
emit(ResultType.Success(_db.userDao.getAll().map { it.toUserDataClass() }))
} catch (ex: HttpException) {
emit(ResultType.Error(ex.localizedMessage))
} catch (ex: IOException) {
emit(ResultType.Error(ex.localizedMessage))
}
}
So, in my viewmodel, I'm collecting the flow like this:
private fun getUsers() {
viewModelScope.launch(Dispatchers.IO) {
_repository.getData(username, password).collect { result ->
when (result) {
is ResultType.Loading -> {
_uiState.update { prev ->
prev.copy(isLoading = true)
}
}
is ResultType.Success -> {
result.data?.let {
_myList = it.toMutableList()
_uiState.update { prev ->
prev.copy(
users = _myList,
isLoading = false
)
}
}
}
}
}
}
Finally, for the UI, the uiState is:
data class UsersState(
val users : List<UserDataClass> = emptyList(),
val isLoading : Boolean = true
)
This is where I'm currently stuck. Because I need to observe for any change in the Room database for those entities
Currently using MVVM for this project.
Let me know if you require more info
You can use flow directly for your Room DAO objects. Don't actually know, how your data classes look like, but will assume:
#Dao
abstract class UsersDAO {
#Query("SELECT * FROM Users")
abstract fun getUsers(): Flow<List<UserDataClass>>
}
Now, every update of the table will emit the new object in the flow. So, in your domain/presentation layer you should simply subscribe to the flow from your DAO.
At first, you need to provide access to dao from your repository
suspend fun getData(): Flow<<List<UserDataClass>> {
try {
val mylist = _api.getUsers(mapparameters).map { it.toUserEntity() }
_db.userDao.delete()
_db.userDao.insertAll(mylist)
} catch (e: Exception) {
// I let you implement catch blocks yourself,
// you probably don't want to emit an error if you want
// observe only actual updates of the table, not the errors
}
return _db.userDao.getUsers() // here you return your flow!
}
Then, in the presentation layer you can do:
private fun getUsers() {
viewModelScope.launch(Dispatchers.IO) {
_repository.getData().collect { usersList ->
// your update logic
}
}
}
Related
I was trying to implement an approach to fetch products from two Data sources (Room & FirebaseFirestore) using Flows.
It was working fine until I noticed that the debugger was returning to the same break point infinitely. When the execution of "ViewmMdel.insertProducts(products)" ends, the debugger returns to Repository.getProducts(//) & repeats.
I changed the approach using only suspending functions & coroutines & works fine but I am curious about how I must to use Flows to implement this approach.
Maybe is only that flatMapMerge is in preview version.
Thanks in advance :D
This one is the implementation:
ViewModel:
fun getProductNames(companyName: String) {
viewModelScope.launch {
repository.getProducts(companyName).catch {
_event.value = AddSaleEvents.ShouldShowLoading(false)
_event.value = AddSaleEvents.ProductsFailureResponse(it.message.toString())
}.collect { products ->
productsList = products
if (products != emptyList<Product>()) {
_event.value = AddSaleEvents.ShouldShowLoading(false)
_event.value = AddSaleEvents.ProductsSuccessfulResponse(products)
insertProducts(products)
} else {
_event.value = AddSaleEvents.ShouldShowLoading(false)
_event.value = AddSaleEvents.ProductsSuccessfulResponse(products)
}
}
}
}
Repository:
#OptIn(FlowPreview::class)
override suspend fun getProducts(compnayName: String): Flow<List<Product>> {
return localDataSource.getProducts().flatMapMerge { list -> // LINE RUNNING INFINITELY
getProductsFromFirebase(list, compnayName)
}.flowOn(Dispatchers.IO).catch {
Log.d("Error", it.message.toString())
}
}
private fun getProductsFromFirebase(products: List<Product>, compnayName: String) = flow {
if (products.isEmpty()) {
remoteDataSource.getProducts(compnayName).collect {
emit(it)
}
} else {
emit(products)
}
}
LocalDataSource with Room:
override suspend fun getProducts(): Flow<List<Product>> = saleDao.getProducts()
Firebase Data Source:
override suspend fun getProducts(company: String): Flow<List<Product>> = flow {
val response = fireStore.collection("products").whereEqualTo("company", company).get()
response.await()
if (response.isSuccessful && !response.result.isEmpty) {
emit(response.result.toObjects(FirebaseProduct::class.java).toEntity())
}
}.catch {
Log.d("Error", it.message.toString())
}
How can I chain the response of a flow to trigger another one inside the MVVM Architecture + Clean Architecture?
6 if it is possible, I want to understand the reason the code is repeating infinitely.
Looks like insertProducts(products) triggers room's DAO.
So localDataSource.getProducts() is a observable read query
Observable queries are read operations that emit new values whenever there are changes to any of the tables that are referenced by the query.
Try to change LocalDataSource
interface SaleDao {
// fun getProducts(): Flow<List<Product>>
suspend fun getProducts(): List<Product>
}
I am working on an Android project and at the moment we are doing multiple network calls in a single repository, for example in the PostsRepository class there are multiple endpoints that needs to be called e.g. (/getNewspost /getPostPrice and maybe /get) then it returns a large Post data class back to the ViewModel.
Although it seems fine, the downside of this structure is being unable to do parallel network calls in the repository like the features of launch, or async/await which only exists in the ViewModel.
So question is can this logic be moved to the ViewModel so then i can do multiple network calls ? Or if this logic should stay in the repository how can we do parallel calls in the repo?
You can create coroutine in Repository class also.
Class PostsRepository{
suspend fun callAPIs() : String{
return withContext(Dispatchers.IO) {
val a = async { getPost() }
val b = async { getNews() }
return#withContext a.await() + b.await()
}
}
}
With Clean architecture , you can create a UseCase to handle this behavior
1.first way
Class GetPostsUseCase(private val postRepository : PostRepository){
suspend operator fun invoke():List<Post>{
// we assume that getPosts()
// and getPostsPricies() are also suspend functions
val posts = postRepository.getPosts()
val prices = postRepository.getPostPricies()
return build(posts , prices)
}
private fun build(posts,prices) :List<Post>{
// build your data object here
}
}
/////// OR ////////
Class GetPostsUseCase(private val postRepository : PostRepository){
suspend operator fun invoke():List<Post> = withContext(Dispatchers.IO){
val posts = async{postRepository.getPosts()}
val prices = async { postRepository.getPostPricies() }
posts.await()
prices.await()
return build(posts, prices)
}
private fun build(posts,prices) :List<Post>{
// build your data object here
}
}
You can achieve this by using suspend and withContext
class PostsRepository {
suspend fun fetchPostData(): Post {
return withContext(Dispatchers.IO) {
val fetchA = async { getA() }
val fetchB = async { getB() }
val fetchC = async { getC() }
//More if needed ...
//Then execute waitAll() to get them all as parallel
val (AResult, BResult, CResult) = awaitAll(fetchA, fetchB, fetchC)
//Finally use the result of these fetch when all of them is completed
return#withContext Post(AResult, BResult, CResult)
}
}
}
According to this article Kotlin Flows. What I understand is DataSource emits latestnews list to repository and in repository it's mapping. Then inside of onEach{} method
the mapped list is using for cache function.
Question is I'm trying this method but onEach method isn't sending data to my cache function.
I tried lot's of way but I didn't make it possible. Why this pattern is not working or what is my misstake.
DATASOURCE
class NewsRemoteDataSource(
private val newsApi: NewsApi,
private val refreshIntervalMs: Long = 5000
) {
val latestNews: Flow<List<ArticleHeadline>> = flow {
while(true) {
val latestNews = newsApi.fetchLatestNews()
emit(latestNews) // Emits the result of the request to the flow
delay(refreshIntervalMs) // Suspends the coroutine for some time
}
}
}
// Interface that provides a way to make network requests with suspend functions
interface NewsApi {
suspend fun fetchLatestNews(): List<ArticleHeadline>
}
REPOSITORY
class NewsRepository(
private val newsRemoteDataSource: NewsRemoteDataSource,
private val userData: UserData
) {
val favoriteLatestNews: Flow<List<ArticleHeadline>> =
newsRemoteDataSource.latestNews
.map { news -> news.filter { userData.isFavoriteTopic(it) } }
.onEach { news -> saveInCache(news) }
}
These are what I tried
ExampleDataSource
class DataSource {
val dummyList:List<User> = listOf(User(
firstName = "example", lastName = "example"
),User(firstName = "example1", lastName = "example2"))
fun getData():Flow<List<User>> = flow {
emit(dummyList)
}
}
ExampleRepository
class Repository(val datasource:DataSource,val dao:UserDao) {
suspend fun getdataRepo():Flow<List<User>>{
return datasource.getData().onEach {
addDatabase(it)
}
}
suspend fun addDatabase(list:List<User>){
dao.insertAll(list)
}
}
Example MainActivity
//This is just for testing...
GlobalScope.launch {
Repository(dao = db.userDao(), datasource = DataSource()).getdataRepo()
}
Why addDatabase Function is not working. According to the article it should be working. How can I solve this.
UPDATE
The answer is Flow should be collected somewhere to make all intermediate operations work because they are lazy. (Answered by "bylazy")
I am trying to write a UnitTest for the kotlin-version of networkBoundResource that can be found on serveral sources with several features
Here is my version of it with marker-comments for the following question.
inline fun <ResultType, RequestType> networkBoundResource(
...
coroutineDispatcher: CoroutineDispatcher
) = flow {
emit(Resource.loading(null)) // emit works!
val data = queryDatabase().firstOrNull()
val flow = if (shouldFetch(data)) {
emit(Resource.loading(data)) // emit works!
try {
saveFetchResult(fetch())
query().map { Resource.success(it) }
} catch (throwable: Throwable) {
onFetchFailed(throwable)
query().map { Resource.error(throwable.toString(), it) }
}
} else {
query().map { Resource.success(it) }
}
emitAll(flow) // emitAll does not work!
}.catch { exception ->
emit(Resource.error("An error occurred while fetching data! $exception", null))
}.flowOn(coroutineDispatcher)
This is one of my UnitTests for this code. The code is edited a bit to focus on my question:
#get:Rule
val testCoroutineRule = TestCoroutineRule()
private val coroutineDispatcher = TestCoroutineDispatcher()
#Test
fun networkBoundResource_noCachedData_shouldMakeNetworkCallAndStoreUserInDatabase() = testCoroutineRule.runBlockingTest {
...
// When getAuthToken is called
val result = networkBoundResource(..., coroutineDispatcher).toList()
result.forEach {
println(it)
}
}
The problem is that println(it) is only printing the Resource.loading(null) emissions. But if you have a look at the last line of the flow {} block, you will see that there should be another emission of the val flow. But this emission never arrives in my UnitTest. Why?
I'm not too sure of the complete behaviour, but essentially you want to get a resource, and current flow is all lumped into the FlowCollector<T> which makes it harder to reason and test.
I have never used or seen the Google code before and if I'm honest only glanced at it. My main take away was it had poor encapsulation and seems to break separations of concern - it manages the resource state, and handles all io work one one class. I'd prefer to have 2 different classes to separate that logic and allows for easier testing.
As simple pseudo code I would do something like this :
class ResourceRepository {
suspend fun get(r : Request) : Resource {
// abstract implementation details network request and io
// - this function should only fulfill the request
// can now be mocked for testing
delay(3_000)
return Resource.success(Any())
}
}
data class Request(val a : String)
sealed class Resource {
companion object {
val loading : Resource get() = Loading
fun success(a : Any) : Resource = Success(a)
fun error(t: Throwable) : Resource = Error(t)
}
object Loading : Resource()
data class Success(val a : Any) : Resource()
data class Error(val t : Throwable) : Resource()
}
fun resourceFromRequest(r : Request) : Flow<Resource> =
flow { emit(resourceRepository.get(r)) }
.onStart { emit(Resource.loading) }
.catch { emit(Resource.error(it)) }
This allows you to massively simplify the actual testing of the resourceFromRequest() function as you only have to mock the repository and one method. This allows you to abstract and deal with the networking and io work elsewhere, independently which again can be tested in isolation.
As #MarkKeen suggested, I now created my own implementation and it works quite well. Compared to the code that is going around on SO, this version now injects the coroutineDispatcher for easier testing, it lets flow take care of error handling, it does not contain nested flows and is imho easier to read and understand, too. There is still the side-effect of storing updated data to the database, but I am too tired now to tackle this.
import kotlinx.coroutines.CoroutineDispatcher
import kotlinx.coroutines.flow.*
inline fun <ResultType, RequestType> networkBoundResource(
crossinline query: () -> Flow<ResultType?>,
crossinline fetch: suspend () -> RequestType,
crossinline saveFetchResult: suspend (RequestType) -> Unit,
crossinline shouldFetch: (ResultType?) -> Boolean = { true },
coroutineDispatcher: CoroutineDispatcher
) = flow<Resource<ResultType>> {
// check for data in database
val data = query().firstOrNull()
if (data != null) {
// data is not null -> update loading status
emit(Resource.loading(data))
}
if (shouldFetch(data)) {
// Need to fetch data -> call backend
val fetchResult = fetch()
// got data from backend, store it in database
saveFetchResult(fetchResult)
}
// load updated data from database (must not return null anymore)
val updatedData = query().first()
// emit updated data
emit(Resource.success(updatedData))
}.onStart {
emit(Resource.loading(null))
}.catch { exception ->
emit(Resource.error("An error occurred while fetching data! $exception", null))
}.flowOn(coroutineDispatcher)
One possible UnitTest for this inline fun, which is used in an AuthRepsitory:
#ExperimentalCoroutinesApi
class AuthRepositoryTest {
companion object {
const val FAKE_ID_TOKEN = "FAkE_ID_TOKEN"
}
#get:Rule
val testCoroutineRule = TestCoroutineRule()
private val coroutineDispatcher = TestCoroutineDispatcher()
private val userDaoFake = spyk<UserDaoFake>()
private val mockApiService = mockk<MyApi>()
private val sut = AuthRepository(
userDaoFake, mockApiService, coroutineDispatcher
)
#Before
fun beforeEachTest() {
userDaoFake.clear()
}
#Test
fun getAuthToken_noCachedData_shouldMakeNetworkCallAndStoreUserInDatabase() = testCoroutineRule.runBlockingTest {
// Given an empty database
coEvery { mockApiService.getUser(any()) } returns NetworkResponse.Success(UserFakes.getNetworkUser(), null, HttpURLConnection.HTTP_OK)
// When getAuthToken is called
val result = sut.getAuthToken(FAKE_ID_TOKEN).toList()
coVerifyOrder {
// Then first try to fetch data from the DB
userDaoFake.get()
// Then fetch the User from the API
mockApiService.getUser(FAKE_ID_TOKEN)
// Then insert the user into the DB
userDaoFake.insert(any())
// Finally return the inserted user from the DB
userDaoFake.get()
}
assertThat(result).containsExactly(
Resource.loading(null),
Resource.success(UserFakes.getAppUser())
).inOrder()
}
}
I want to get an API request and save request's data to a DB. Also want to return the data (that is written to DB). I know, this is possible in RxJava, but now I write in Kotlin coroutines, currently use Fuel instead of Retrofit (but a difference is not so large). I read How to use Fuel with a Kotlin coroutine, but don't understand it.
How to write a coroutine and methods?
UPDATE
Say, we have a Java and Retrofit, RxJava. Then we can write a code.
RegionResponse:
#AutoValue
public abstract class RegionResponse {
#SerializedName("id")
public abstract Integer id;
#SerializedName("name")
public abstract String name;
#SerializedName("countryId")
public abstract Integer countryId();
public static RegionResponse create(int id, String name, int countryId) {
....
}
...
}
Region:
data class Region(
val id: Int,
val name: String,
val countryId: Int)
Network:
public Single<List<RegionResponse>> getRegions() {
return api.getRegions();
// #GET("/regions")
// Single<List<RegionResponse>> getRegions();
}
RegionRepository:
fun getRegion(countryId: Int): Single<Region> {
val dbSource = db.getRegion(countryId)
val lazyApiSource = Single.defer { api.regions }
.flattenAsFlowable { it }
.map { apiMapper.map(it) }
.toList()
.doOnSuccess { db.updateRegions(it) }
.flattenAsFlowable { it }
.filter({ it.countryId == countryId })
.singleOrError()
return dbSource
.map { dbMapper.map(it) }
.switchIfEmpty(lazyApiSource)
}
RegionInteractor:
class RegionInteractor(
private val repo: RegionRepository,
private val prefsRepository: PrefsRepository) {
fun getRegion(): Single<Region> {
return Single.fromCallable { prefsRepository.countryId }
.flatMap { repo.getRegion(it) }
.subscribeOn(Schedulers.io())
}
}
Let's look at it layer by layer.
First, your RegionResponse and Region are totally fine for this use case, as far as I can see, so we won't touch them at all.
Your network layer is written in Java, so we'll assume it always expects synchronous behavior, and won't touch it either.
So, we start with the repo:
fun getRegion(countryId: Int) = async {
val regionFromDb = db.getRegion(countryId)
if (regionFromDb == null) {
return apiMapper.map(api.regions).
filter({ it.countryId == countryId }).
first().
also {
db.updateRegions(it)
}
}
return dbMapper.map(regionFromDb)
}
Remember that I don't have your code, so maybe the details will differ a bit. But the general idea with coroutines, is that you launch them with async() in case they need to return the result, and then write your code as if you were in the perfect world where you don't need to concern yourself with concurrency.
Now to the interactor:
class RegionInteractor(
private val repo: RegionRepository,
private val prefsRepository: PrefsRepository) {
fun getRegion() = withContext(Schedulers.io().asCoroutineDispatcher()) {
val countryId = prefsRepository.countryId
return repo.getRegion(countryId).await()
}
}
You need something to convert from asynchronous code back to synchronous one. And for that you need some kind of thread pool to execute on. Here we use thread pool from Rx, but if you want to use some other pool, so do.
After researching How to use Fuel with a Kotlin coroutine, Fuel coroutines and https://github.com/kittinunf/Fuel/ (looked for awaitStringResponse), I made another solution. Assume that you have Kotlin 1.3 with coroutines 1.0.0 and Fuel 1.16.0.
We have to avoid asynhronous requests with callbacks and make synchronous (every request in it's coroutine). Say, we want to show a country name by it's code.
// POST-request to a server with country id.
fun getCountry(countryId: Int): Request =
"map/country/"
.httpPost(listOf("country_id" to countryId))
.addJsonHeader()
// Adding headers to the request, if needed.
private fun Request.addJsonHeader(): Request =
header("Content-Type" to "application/json",
"Accept" to "application/json")
It gives a JSON:
{
"country": {
"name": "France"
}
}
To decode the JSON response we have to write a model class:
data class CountryResponse(
val country: Country,
val errors: ErrorsResponse?
) {
data class Country(
val name: String
)
// If the server prints errors.
data class ErrorsResponse(val message: String?)
// Needed for awaitObjectResponse, awaitObject, etc.
class Deserializer : ResponseDeserializable<CountryResponse> {
override fun deserialize(content: String) =
Gson().fromJson(content, CountryResponse::class.java)
}
}
Then we should create a UseCase or Interactor to receive a result synchronously:
suspend fun getCountry(countryId: Int): Result<CountryResponse, FuelError> =
api.getCountry(countryId).awaitObjectResponse(CountryResponse.Deserializer()).third
I use third to access response data. But if you wish to check for a HTTP error code != 200, remove third and later get all three variables (as Triple variable).
Now you can write a method to print the country name.
private fun showLocation(
useCase: UseCaseImpl,
countryId: Int,
regionId: Int,
cityId: Int
) {
GlobalScope.launch(Dispatchers.IO) {
// Titles of country, region, city.
var country: String? = null
var region: String? = null
var city: String? = null
val countryTask = GlobalScope.async {
val result = useCase.getCountry(countryId)
// Receive a name of the country if it exists.
result.fold({ response -> country = response.country.name }
, { fuelError -> fuelError.message })
}
}
val regionTask = GlobalScope.async {
val result = useCase.getRegion(regionId)
result.fold({ response -> region = response.region?.name }
, { fuelError -> fuelError.message })
}
val cityTask = GlobalScope.async {
val result = useCase.getCity(cityId)
result.fold({ response -> city = response.city?.name }
, { fuelError -> fuelError.message })
}
// Wait for three requests to execute.
countryTask.await()
regionTask.await()
cityTask.await()
// Now update UI.
GlobalScope.launch(Dispatchers.Main) {
updateLocation(country, region, city)
}
}
}
In build.gradle:
ext {
fuelVersion = "1.16.0"
}
dependencies {
...
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.0.0'
// Fuel.
//for JVM
implementation "com.github.kittinunf.fuel:fuel:${fuelVersion}"
//for Android
implementation "com.github.kittinunf.fuel:fuel-android:${fuelVersion}"
//for Gson support
implementation "com.github.kittinunf.fuel:fuel-gson:${fuelVersion}"
//for Coroutines
implementation "com.github.kittinunf.fuel:fuel-coroutines:${fuelVersion}"
// Gson.
implementation 'com.google.code.gson:gson:2.8.5'
}
If you want to work with coroutines and Retrofit, please, read https://medium.com/exploring-android/android-networking-with-coroutines-and-retrofit-a2f20dd40a83 (or https://habr.com/post/428994/ in Russian).
You should be able to significantly simplify your code. Declare your use case similar to the following:
class UseCaseImpl {
suspend fun getCountry(countryId: Int): Country =
api.getCountry(countryId).awaitObject(CountryResponse.Deserializer()).country
suspend fun getRegion(regionId: Int): Region =
api.getRegion(regionId).awaitObject(RegionResponse.Deserializer()).region
suspend fun getCity(countryId: Int): City=
api.getCity(countryId).awaitObject(CityResponse.Deserializer()).city
}
Now you can write your showLocation function like this:
private fun showLocation(
useCase: UseCaseImpl,
countryId: Int,
regionId: Int,
cityId: Int
) {
GlobalScope.launch(Dispatchers.Main) {
val countryTask = async { useCase.getCountry(countryId) }
val regionTask = async { useCase.getRegion(regionId) }
val cityTask = async { useCase.getCity(cityId) }
updateLocation(countryTask.await(), regionTask.await(), cityTask.await())
}
}
You have no need to launch in the IO dispatcher because your network requests are non-blocking.
I must also note that you shouldn't launch in the GlobalScope. Define a proper coroutine scope that aligns its lifetime with the lifetime of the Android activity or whatever else its parent is.