This is what I want to do:
call first rest API
if first succeeds call seconds rest API
if both are successful -> create an aggregated response
I'm using RxJava2 in Micronaut.
This is what I have but I'm not sure it's correct. What would happen if the first or second API call fails?
#Singleton
public class SomeService {
private final FirstRestApi firstRestApi;
private final SecondRestApi secondRestApi;
public SomeService(FirstRestApi firstRestApi, SecondRestApi secondRestApi) {
this.firstRestApi = firstRestApi;
this.secondRestApi = secondRestApi;
}
public Single<AggregatedResponse> login(String data) {
Single<FirstResponse> firstResponse = firstRestApi.call(data);
Single<SecondResponse> secondResponse = secondRestApi.call();
return firstResponse.zipWith(secondResponse, this::convertResponse);
}
private AggregatedResponse convertResponse(FirstResponse firstResponse, SecondResponse secondResponse) {
return AggregatedResponse
.builder()
.something1(firstResponse.getSomething1())
.something2(secondResponse.getSomething2())
.build();
}
}
This should be as simple as
public Single<AggregatedResponse> login(String data) {
return firstRestApi.call(data)
.flatMap((firstResponse) -> secondRestApi.call().map((secondResponse) -> {
return Pair.create(firstResponse, secondResponse);
})
.map((pair) -> {
return convertResponse(pair.getFirst(), pair.getSecond());
});
}
In which case you no longer need zipWith. Errors just go to error stream as usual.
Related
I working on a Quarkus + MongoDB Reactive+ Mutiny application. I have a Person object and Event Object. I am creating a new event for a person. My uri looks like this
POST /person/{personId}/event
I need to first check if the person exists in MongoDB. If the person exists then save event. If person does not exist then create a Error Status and return. I am tried everything but I am stuck and getting error that required return type is Uni but required type is Uni. I tried with transformToUni as well but it did not work. Also tried few other ways like onItemOrFailure() etc. but nothing seems to work.
Here's the full Code.
public class EventResource {
#Inject
EventRepository eventRepository;
#Inject
PersonRepository personRepository;
#POST
#Path("/{person_id}/event")
public Uni<Response> create(Event event, #PathParam("person_id") String personId){
//Check if personId exist.
Uni<Person> uniPerson = personRepository.getPersonById(personId);
//THIS WORKS BUT ON FAILURE IS TREATED WHEN ERROR IS RAISED FOR EeventRepository.craete() and not if person is not found.
/*return uniPerson.onItem().ifNotNull()
.transformToUni(pid -> eventRepository.create(event, pid.getId()))
.onItem().transform(e -> Response.ok().entity(e).build())
.onFailure()
.recoverWithItem(f-> {
AStatus status = createErrorStatus(f.getMessage());
return Response.serverError().entity(status).build();
});
*/
Uni<Response> eventResp = uniPerson.onItem().transform(person -> {
if(person==null)
return Response.serverError().build();
else{
return eventRepository.create(event, person.getId())
.onItem().transform(event1 -> Response.ok(event1).build());
}
});
return eventResp;
}
You can use mutiny ifNull:
#POST
#Path("/{person_id}/event")
public Uni<Response> create(Event event, #PathParam("person_id") String personId){
return personRepository
.getPersonById(personId)
.onItem().ifNotNull().transformToUni(person -> createEvent(event, person))
.onItem().ifNull().continueWith(this::personNotFound)
// This onFailure will catch all the errors
.onFailure()
.recoverWithItem(f-> {
AStatus status = createErrorStatus(f.getMessage());
return Response.serverError().entity(status).build();
});
}
private Uni<Response> createEvent(Event event, Person person) {
return eventRepository
.create(event, person.getId())
.map( e -> Response.ok().entity(e).status(CREATED).build())
}
private Response personNotFound() {
return Response.serverError().build();
}
The error you are seeing is because when the item is not null, you are returning a Uni<Uni<Response>>. This is one way to fix it:
Uni<Response> eventResp = uniPerson
.chain(person -> {
if (person==null)
return Uni.createFrom().item(Response.serverError().build());
else {
return eventRepository
.create(event, person.getId())
.map(event1 -> Response.ok(event1).build());
}
});
I'm using map and chain because they are shorter, but you can replace them with onItem().transform(...) and onItem().transformToUni(...).
I have two operations step_1() and step_2() and want to execute step_2() AFTER step_1().
With normal java this would be:
step_1();
step_2();
With vertx I have to use vertx-compose(). Am I right?
According to https://groups.google.com/forum/#!topic/vertx/FuvlPLpoGOA, I dont need Futures for sequential code.
"If you want to do each request sequencially you dont need futures."
So how can I do that without using futures?
I dont know, if this matters: My Vertx from which this code is executed is a "Worker"-Verticle.
#Override
public void start(Future<Void> fut) throws IOException {
Future<Void> step_1 = Future.future();
step_1.compose(res -> {
// If the future succeeded
Future<Void> step_2 = step_1();
step_2.compose(res2 -> {
step_2();
}, Future.future().setHandler(handler -> {
// If the future failed
}));
//I dont need that
}, Future.future().setHandler(handler -> {
// If the future failed
}));
}
public void step_1(){
..
}
public void step_2(){
..
}
Is this the right and shortest (!) way?
Below is an example of chaining of Future, I have made the example very trivial nonetheless it showcases the concept.
#RunWith(VertxUnitRunner.class)
public class Chaining {
private Vertx vertx = Vertx.vertx();
#Test
public void futures_chaining(TestContext context) throws Exception {
Async async = context.async();
firstOperation()
.compose((outcome) -> {
System.out.println(outcome);
return secondOperation();
})
.compose(outcome -> {
System.out.println(outcome);
/*
For stopping unit test we are returning this future
for production use-case this would be Future.succeededFuture
or Future.failedFuture depending on your method outcomes
*/
return Future.future(handle -> async.complete());
});
}
private Future<String> firstOperation() {
Future<String> future = Future.future();
vertx.setTimer(1000, delay -> future.complete("First Operation Complete"));
return future;
}
private Future<String> secondOperation() {
Future<String> future = Future.future();
vertx.setTimer(1000, delay -> future.complete("Second Operation Complete"));
return future;
}
}
"If you want to do each request sequencially you dont need futures."
No, it's not. In asynchronous frameworks like Vert.x, input/output operations are non-blocking. It means, that if you call few asynchronous operations, they'll start working simultaneously. And if you want to do few requests sequentially, then you should use futures or callbacks to execute new request only after previous one finished successfully.
Check this code with futures, newer version with RxJava 2 and article about project.
#Override
public Future<Optional<Todo>> getCertain(String todoID) {
Future<Optional<Todo>> result = Future.future();
redis.hget(Constants.REDIS_TODO_KEY, todoID, res -> {
if (res.succeeded()) {
result.complete(Optional.ofNullable(
res.result() == null ? null : new Todo(res.result())));
} else
result.fail(res.cause());
});
return result;
}
#Override
public Future<Todo> update(String todoId, Todo newTodo) {
return this.getCertain(todoId).compose(old -> {
if (old.isPresent()) {
Todo fnTodo = old.get().merge(newTodo);
return this.insert(fnTodo)
.map(r -> r ? fnTodo : null);
} else {
return Future.succeededFuture();
}
});
}
RxJava exists specifically to compose async events: http://vertx.io/docs/vertx-rx/java/
Assuming both step_1() and step_1() aren't designed to return results (i.e. they effectively return void) then you could change them to return Observable or Single and chain them together similar to this:
step_1().doOnSuccess(this::step_2()).subscribe(/* control resumes here */);
RxJava (or rather, reactive programming in general) takes a little bit to wrap your head around it, but I would strongly recommend using it if you're planning to chain together async operations.
Pass step_2 as argument to step_1
#Override
public void start(Future<Void> fut) throws IOException {
step_1(step_2);
}
private void step_1(Runnable function){
someAsynccall("some-arg", response -> {
function.run();
}).end();
}
private void step_2(){
// do something
}
I need to recollect some data calling to a method is connecting to a webservice.
problem: Imagine I need to update the content text of a label control according to this remote gathered information. Until all this data is recollected I'm not going to be able to show the label.
desired: I'd like to first show the label with a default text, and as I'm receiving this information I want to update the label content (please, don't take this description as a sucked code, I'm trying to brief my real situation).
I'd like to create an observable sequence of these methods. Nevertheless, these method have not the same signature. For example:
int GetInt() {
return service.GetInt();
}
string GetString() {
return service.GetString();
}
string GetString2 {
return service.GetString2();
}
These methods are not async.
Is it possible to create an observable sequence of these methods?
How could I create it?
Nevertheless, which's the best alternative to achieve my goal?
Creating custom observable sequences can be achieved with the Observable.Create. An example using your requirements is shown below:
private int GetInt()
{
Thread.Sleep(1000);
return 1;
}
private string GetString()
{
Thread.Sleep(1000);
return "Hello";
}
private string GetString2()
{
Thread.Sleep(2000);
return "World!";
}
private IObservable<string> RetrieveContent()
{
return Observable.Create<string>(
observer =>
{
observer.OnNext("Default Text");
int value = GetInt();
observer.OnNext($"Got value {value}. Getting string...");
string string1 = GetString();
observer.OnNext($"Got string {string1}. Getting second string...");
string string2 = GetString2();
observer.OnNext(string2);
observer.OnCompleted();
return Disposable.Empty;
}
);
}
Note how I have emulated network delay by introducing a Thread.Sleep call into each of the GetXXX methods. In order to ensure your UI doesn't hang when subscribing to this observable, you should subscribe as follows:
IDisposable subscription = RetrieveContent()
.SubscribeOn(TaskPoolScheduler.Default)
.ObserveOn(DispatcherScheduler.Current)
.Subscribe(text => Label = text);
This code uses the .SubscribeOn(TaskPoolScheduler.Default) extension method to use a TaskPool thread to start the observable sequence and will be blocked by the calls the Thread.Sleep but, as this is not the UI thread, your UI will remain responsive. Then, to ensure we update the UI on the UI thread, we use the ".ObserveOn(DispatcherScheduler.Current)" to invoke the updates onto the UI thread before setting the (data bound) Label property.
Hope this is what you were looking for, but leave a comment if not and I'll try to help further.
I would look at creating a wrapper class for your service to expose the values as separate observables.
So, start with a service interface:
public interface IService
{
int GetInt();
string GetString();
string GetString2();
}
...and then you write ServiceWrapper:
public class ServiceWrapper : IService
{
private IService service;
private Subject<int> subjectGetInt = new Subject<int>();
private Subject<string> subjectGetString = new Subject<string>();
private Subject<string> subjectGetString2 = new Subject<string>();
public ServiceWrapper(IService service)
{
this.service = service;
}
public int GetInt()
{
var value = service.GetInt();
this.subjectGetInt.OnNext(value);
return value;
}
public IObservable<int> GetInts()
{
return this.subjectGetInt.AsObservable();
}
public string GetString()
{
var value = service.GetString();
this.subjectGetString.OnNext(value);
return value;
}
public IObservable<string> GetStrings()
{
return this.subjectGetString.AsObservable();
}
public string GetString2()
{
var value = service.GetString2();
this.subjectGetString2.OnNext(value);
return value;
}
public IObservable<string> GetString2s()
{
return this.subjectGetString2.AsObservable();
}
}
Now, assuming that you current service is called Service, you would write this code to set things up:
IService service = new Service();
ServiceWrapper wrapped = new ServiceWrapper(service); // Still an `IService`
var subscription =
Observable
.Merge(
wrapped.GetInts().Select(x => x.ToString()),
wrapped.GetStrings(),
wrapped.GetString2s())
.Subscribe(x => label.Text = x);
IService wrappedService = wrapped;
Now pass wrappedService instead of service to your code. It's still calling the underlying service code so no need for a re-write, yet you still are getting the observables that you want.
This is effectively a gang of four decorator pattern.
I have method called selectAll which has to return records selected from database, but when I want to return them as String it doesn't allow it and gives me:
Local variable S defined in an enclosing scope must be final or effectively final.
I tried to add final to my String but it stills the same.
Here is my selectAll() method:
public String selectAll(String table, String order) {
String S;
S = "";
this.getCnx().getConnection(res -> {
if (res.succeeded()) {
SQLConnection connection = res.result();
connection.queryWithParams(ReqSql.SELECT_ALL, new JsonArray().add(table).add(order), (ar) -> {
if (ar.failed()) {
this.sendError(500, response);
} else {
JsonArray arr = new JsonArray();
ar.result().getRows().forEach(arr::add);
S = ar.result().getRows().toString();
response.putHeader("content-type", "application/json").end(arr.encode());
}
});
}
});
}
public AsyncSQLClient getCnx(){
JsonObject mySQLClientConfig = new JsonObject()
.put("host", "localhost")
.put("database", "test")
.put("username", "test")
.put("password", "test")
.put("port", 3306);
return MySQLClient.createShared(vertx, mySQLClientConfig);
}
And I create another class for my requests:
public class ReqSql {
public static final String SELECT_ALL = "SELECT * FROM ? ORDER BY ? ASC";
}
Regards.
Problem is that you need to declare local variables as final if you want to use them in a Lambda expression. But you cannot assign a value to a final variable. So this will not work:
final String S = "";
this.getCnx().getConnection(res -> {
//...
S = ar.result().getRows().toString();
//...
});
Vert.x is highly asynchronous. That means that most operations, like getConnection(), will infect return immediately but their results, in this case SQLConnection, will be available to the Handler to a later point in time.
If you try to make a asynchronous result available in the main program flow that wouldn't work. What every you want to do with S is probably wrong. So if you don't need S afterwards I would convert S to a local variable.
I suggest you read about Future in the documentation. A Future is a placeholder for results of asynchronous calls. Vert.x is full of asynchronous calls. With Future you can do something like this:
Future<SQLConnection> connection = Future.future();
this.getCnx().getConnection(res -> {
if (res.succeeded()) {
logger.info("Got a connection.");
connection.complete(res.result());
} else {
connection.fail(res.cause());
}
});
You specify a Handler on a Future for retrieving the asynchronous result in a much more readable manner than callbacks/Lambdas:
connection.setHandler(res -> {
...
})
The project I'm working on has the Entity Framework on top of an OData layer. The Odata layer has it's server side pagination turned to a value of 75. My reading on the subject leads me to believe that this pagination value is used across the board, rather than a per table basis. The table that I'm currently looking to extract all the data from is, of course, more than 75 rows. Using the entity framework, my code is simply thus:
public IQueryable<ProductColor> GetProductColors()
{
return db.ProductColors;
}
where db is the entity context. This is returning the first 75 records. I read something where I could append a parameter inlinecount set to allpages giving me the following code:
public IQueryable<ProductColor> GetProductColors()
{
return db.ProductColors.AddQueryOption("inlinecount","allpages");
}
However, this too returns 75 rows!
Can anyone shed light on how to truly get all the records regardless of the OData server-side pagination stuff?
important: I cannot remove the pagination or turn it off! It's extremely valuable in other scenarios where performance is a concern.
Update:
Through some more searching I've found an MSDN that describes how to do this task.
I'd love to be able to turn it into a full Generic method but, this was as close as I could get to a generic without using reflection:
public IQueryable<T> TakeAll<T>(QueryOperationResponse<T> qor)
{
var collection = new List<T>();
DataServiceQueryContinuation<T> next = null;
QueryOperationResponse<T> response = qor;
do
{
if (next != null)
{
response = db.Execute<T>(next) as QueryOperationResponse<T>;
}
foreach (var elem in response)
{
collection.Add(elem);
}
} while ((next = response.GetContinuation()) != null);
return collection.AsQueryable();
}
calling it like:
public IQueryable<ProductColor> GetProductColors()
{
QueryOperationResponse<ProductColor> response = db.ProductColors.Execute() as QueryOperationResponse<ProductColor>;
var productColors = this.TakeAll<ProductColor>(response);
return productColors.AsQueryable();
}
If unable turn off paging you'll receive 75 row by call, always. You can get all rows in following ways:
Add another IQueryable<ProductColor> AllProductColors and modify
public static void InitializeService(DataServiceConfiguration config)
{
config.UseVerboseErrors = true;
config.SetEntitySetAccessRule("*", EntitySetRights.AllRead);
config.SetEntitySetPageSize("ProductColors", 75); - Note only paged queries are present
config.SetServiceOperationAccessRule("*", ServiceOperationRights.AllRead);
config.DataServiceBehavior.MaxProtocolVersion = DataServiceProtocolVersion.V2;
}
You should call ProductColors as many as needed, for example
var cat = new NetflixCatalog(new Uri("http://odata.netflix.com/v1/Catalog/"));
var x = from t in cat.Titles
where t.ReleaseYear == 2009
select t;
var response = (QueryOperationResponse<Title>)((DataServiceQuery<Title>)x).Execute();
while (true)
{
foreach (Title title in response)
{
Console.WriteLine(title.Name);
}
var continuation = response.GetContinuation();
if (continuation == null)
{
break;
}
response = cat.Execute(continuation);
}
I use Rx with following code
public sealed class DataSequence<TEntry> : IObservable<TEntry>
{
private readonly DataServiceContext context;
private readonly Logger logger = LogManager.GetCurrentClassLogger();
private readonly IQueryable<TEntry> query;
public DataSequence(IQueryable<TEntry> query, DataServiceContext context)
{
this.query = query;
this.context = context;
}
public IDisposable Subscribe(IObserver<TEntry> observer)
{
QueryOperationResponse<TEntry> response;
try
{
response = (QueryOperationResponse<TEntry>)((DataServiceQuery<TEntry>)query).Execute();
if (response == null)
{
return Disposable.Empty;
}
}
catch (Exception ex)
{
logger.Error(ex);
return Disposable.Empty;
}
var initialState = new State
{
CanContinue = true,
Response = response
};
IObservable<TEntry> sequence = Observable.Generate(
initialState,
state => state.CanContinue,
MoveToNextState,
GetCurrentValue,
Scheduler.ThreadPool).Merge();
return new CompositeDisposable(initialState, sequence.Subscribe(observer));
}
private static IObservable<TEntry> GetCurrentValue(State state)
{
if (state.Response == null)
{
return Observable.Empty<TEntry>();
}
return state.Response.ToObservable();
}
private State MoveToNextState(State state)
{
DataServiceQueryContinuation<TEntry> continuation = state.Response.GetContinuation();
if (continuation == null)
{
state.CanContinue = false;
return state;
}
QueryOperationResponse<TEntry> response;
try
{
response = context.Execute(continuation);
}
catch (Exception)
{
state.CanContinue = false;
return state;
}
state.Response = response;
return state;
}
private sealed class State : IDisposable
{
public bool CanContinue { get; set; }
public QueryOperationResponse<TEntry> Response { get; set; }
public void Dispose()
{
CanContinue = false;
}
}
}
so for get any data thru OData, create a sequence and Rx does the rest
var sequence = new DataSequence<Product>(context.Products, context);
sequence.OnErrorResumeNext(Observable.Empty<Product>())
.ObserveOnDispatcher().SubscribeOn(Scheduler.NewThread).Subscribe(AddProduct, logger.Error);
The page size is set by the service author and can be set per entity set (but a service may choose to apply the same page size to all entity sets). There's no way to avoid it from the client (which is by design since it's a security feature).
The inlinecount option asks the server to include the total count of the results (just the number), it doesn't disable the paging.
From the client the only way to read all the data is to issue the request which will return the first page and it may contain a next link which you request to read the next page and so on until the last response doesn't have the next link.
If you're using the WCF Data Services client library it has support for continuations (the next link) and a simple sample can be found in this blog post (for example): http://blogs.msdn.com/b/phaniraj/archive/2010/04/25/server-driven-paging-with-wcf-data-services.aspx