We are working on service which collect data from AWS SQS then send batch to client. We are using mediator to publish notifications. The diagram of program looks like:
The problem is in first NotificationHandler from Mediatr.
private readonly EventCollectorHostedService _collector;
public CollectIncomingEventNotificationHandler(EventCollectorHostedService collector)
{
_collector = collector;
}
Class EventCollectorHostedService is register after Mediator so is not visible during registering this NotificationHandler and additionally it use Mediator to publish notification that batch is ready to send.
The error is that cannot construct CollectIncomingEventNotificationHandler because -> Unable to resolve service for type 'Api.Services.HostedServices.EventCollectorHostedService'.
services.AddMediatR(typeof(Startup).GetTypeInfo().Assembly);
services.AddHostedService<EventCollectorHostedService>();
The ugly solution is to declare some functionality in EventCollectorHostedService as static or instead of injecting EventCollectorHostedService, inject IServiceProvider.
But these solution don't look clean for me so do you have any other better solution ?
Thanks in advance.
Maybe someone encountered with similar problem so finally i have a brilliant solution.
Background services have to be treat like separate microservices based on event driven architecture so we have to make internal message broker mechanism.
The very simple solution which cover my case is:
public class NotificationChannel : INotificationChannel
{
public event EventHandler<IncomingEventNotificataionEventArgs> IncomingEventReceived;
public void Publish<T>(T notification)
{
if(notification is IncomingEventNotification incomingEventNotification)
{
OnIncomingEventReceived(incomingEventNotification);
}
}
protected virtual void OnIncomingEventReceived(IncomingEventNotification notification)
{
if(IncomingEventReceived != null)
{
var args = new IncomingEventNotificataionEventArgs(notification);
IncomingEventReceived(this, args);
}
}
}
Related
Someone out there must have run into this already...
I created a WebApi solution with swagger implemented, full documentation, the whole 9 yards!
When I run my web api solution, see the swagger output (and I've tested the endpoints, all working fine)
I can see the swagger definition: https://localhost:5001/swagger/v1/swagger.json
Now, I want to consume this Api as a connected service on my web app.
So following every single tutorial online:
I go to my webapp
right click on Connected Services
Add Connected Service
Add Service Reference > OpenApi > add Url, namespace & class name
That generates a partial class in my solution (MyTestApiClient)
public parial class MyTestApiClient
{
// auto generated code
}
Next step, inject the service in Startup.cs
services.AddTransient(x =>
{
var client = new MyTestApiClient("https://localhost:5001", new HttpClient());
return client;
});
Then, inject the class into some class where it's consumed and this all works
public class TestService
{
private readonly MyTestApiClient _client; // this is class, not an interface -> my problem
public TestService(MyTestApiClient client)
{
_client = client;
}
public async Task<int> GetCountAsync()
{
return _client.GetCountAsync();
}
}
So everything up to here works. BUT, this generated OpenApi client doesn't have an interface which sucks for the purposes of DI and Unit Testing.
I got around this by creating a local interface IMyTestApiClient, added to the generated class (MyTestApiClient). I only have 1 endpoint in my WebApi so have to declare that on my interface.
public parial class MyTestApiClient : IMyTestApiClient
{
// auto generated code
}
public interface IMyTestApiClient
{
// implemented in generated MyTestApiClient class
Task<int> GetCountAsync();
}
services.AddTransient<IMyTestApiClient, MyTestApiClient>(x =>
{
IMyTestApiClient client = new MyTestApiClient("https://localhost:5001", new HttpClient());
return client;
});
public class TestService
{
private readonly IMyTestApiClient _client; // now injecting local interface instead of the generated class - great success
public TestService(IMyTestApiClient client)
{
_client = client;
}
public async Task<int> GetCountAsync()
{
return _client.GetCountAsync();
}
}
But this is a bad approach because it makes me manually create an interface and explicitly declare the methods I want to consume. Furthermore, every time my Api gets updated, I will have to tweak my local interface.
So question time:
How can I add an OpenApi Service Reference that automagically also generates an interface as well?
Thanks in advance for any help getting to a viable solution.
You may have already found the answer but I had the same issue and managed to resolve it by adding /GenerateClientInterfaces:true in the Options section for the OpenAPI reference in my .csproj:
<OpenApiReference Include="api.json" CodeGenerator="NSwagCSharp" Namespace="MyNamespace" ClassName="MyClassName">
<SourceUri>https://localhost:7040/swagger/v1/swagger.json</SourceUri>
<OutputPath>MyClient.cs</OutputPath>
<Options>/GenerateClientInterfaces:true</Options>
</OpenApiReference>
How can I dispose and re-instantiate a singleton with Prism/DryIoC in Xamarin Forms?
I'm working with Azure Mobile Apps for offline data. Occasionally, I need to delete the local sqlite database and re-initialize it. Unfortunately the MobileServiceClient occasionally holds the db connection open and there's no method exposed to close it. The suggested solution (https://github.com/Azure/azure-mobile-apps-net-client/issues/379) is to dispose of MobileServiceClient. Only problem is that is registered with DryIoC as a singleton.
I'm not overly familiar with DryIoC, or Prism and Forms for that matter... But for the life of me, I can't see a way to do this.
I did cook up a pretty elaborate scheme that almost worked.
In my ViewModel method, when I needed the db freed up, I fired off an event -
_eventAggregator.GetEvent<RegisterDatabaseEvent>().Publish(false);
Then in App.xaml.cs, I wired up a listener and a handler like so -
_eventAggregator.GetEvent<RegisterDatabaseEvent>().Subscribe(OnRegisterDatabaseEventPublished);
private void OnRegisterDatabaseEventPublished()
{
Container.GetContainer().Unregister<IAppMobileClient>();
Container.GetContainer().Unregister<IMobileServiceClient>();
Container.GetContainer().Register<IMobileServiceClient, AppMobileClient>(new SingletonReuse());
Container.GetContainer().Register<IAppMobileClient, AppMobileClient>(new SingletonReuse());
_eventAggregator.GetEvent<RegisterDatabaseCompletedEvent>().Publish(register);
}
Lastly, back in the ViewModel constructor, I had a final listener that handled the event coming back from App.xaml and finished processing.
_eventAggregator.GetEvent<RegisterDatabaseCompletedEvent>().Subscribe(OnRegisterDatabaseCompletedEventPublished);
So the amazing thing is that this worked. The database was able to be deleted and all was good. But then I navigated to a different page and BOOM. DryIoC said it couldn't wire up the ViewModel for that page. I assume the unregister/register jacked up DryIoC for all injection... So how can I accomplish what needs to be done?
FINAL SOLUTION
Thanks so much to dadhi for taking the time to help. You are certainly a class act and I'm now considering using DryIoC elsewhere.
For anyone who stumbles on this, I'm posting the final solution below. I'll be as verbose as I can to avoid any confusion.
First, in my App.xaml.cs, I added a method for registering my database.
public void RegisterDatabase(IContainer container)
{
container.RegisterMany<AppMobileClient>(Reuse.Singleton,
setup: Setup.With(asResolutionCall: true),
ifAlreadyRegistered: IfAlreadyRegistered.Replace,
serviceTypeCondition: type =>
type == typeof(IMobileServiceClient) || type == typeof(IAppMobileClient));
}
I simply add a call to that method in RegisterTypes in place of registering the types in there directly.
protected override void RegisterTypes(IContainerRegistry containerRegistry)
{
containerRegistry.GetContainer().Rules.WithoutEagerCachingSingletonForFasterAccess();
...
RegisterDatabase(containerRegistry.GetContainer());
...
}
Note also the added rule for eager caching, per dadhi.
Later on when I need to release the database in the ViewModel... I kick things off by resetting my local db variable and sending an event to App.xaml.cs
_client = null;
_eventAggregator.GetEvent<RegisterDatabaseEvent>().Publish(true);
In App.xaml.cs, I have subscribed to that event and tied it to the following method.
private void OnRegisterDatabaseEventPublished()
{
RegisterDatabase(Container.GetContainer());
_eventAggregator.GetEvent<RegisterDatabaseCompletedEvent>().Publish(register);
}
Here I just call RegisterMany again, exactly the same as I do when the app starts up. No need to unregister anything. With the setup and ifAlreadyRegistered arguments (thanks, dadhi!), DryIoC allows the object to be replaced. Then I raise an event back to the VM letting it know the database has been released.
Finally, back in the ViewModel, I'm listening for the completed event. The handler for that event updates the local copy of the object like so.
_client = ((PrismApplication)App.Current).Container.Resolve<IAppMobileClient>();
And then I can work with the new object, as needed. This is key. Without setting _client to null above and resolving it again here, I actually ended up with 2 copies of the object and calls to methods were being hit 2x.
Hope that helps someone else looking to release their Azure Mobile Apps database!
I am not sure how exactly XF handles these things.
But in DryIoc in order for service to be fully deleted or replaced it need to be registered with setup: Setup.With(asResolutionCall: true). Read here for more details: https://bitbucket.org/dadhi/dryioc/wiki/UnregisterAndResolutionCache#markdown-header-unregister-and-resolution-cache
Update
Here are two options and considerations that work in pure DryIoc and may not work XF. But it probably may help with solution.
public class Foo
{
public IBar Bar { get; private set; }
public Foo(IBar bar) { Bar = bar; }
}
public interface IBar {}
public class Bar : IBar {}
public class Bar2 : IBar { }
[Test]
public void Replace_singleton_dependency_with_asResolutionCall()
{
var c = new Container(rules => rules.WithoutEagerCachingSingletonForFasterAccess());
c.Register<Foo>();
//c.Register<Foo>(Reuse.Singleton); // !!! If the consumer of replaced dependency is singleton, it won't work
// cause the consumer singleton should be replaced too
c.Register<IBar, Bar>(Reuse.Singleton,
setup: Setup.With(asResolutionCall: true)); // required
var foo = c.Resolve<Foo>();
Assert.IsInstanceOf<Bar>(foo.Bar);
c.Register<IBar, Bar2>(Reuse.Singleton,
setup: Setup.With(asResolutionCall: true), // required
ifAlreadyRegistered: IfAlreadyRegistered.Replace); // required
var foo2 = c.Resolve<Foo>();
Assert.IsInstanceOf<Bar2>(foo2.Bar);
}
[Test]
public void Replace_singleton_dependency_with_UseInstance()
{
var c = new Container();
c.Register<Foo>();
//c.Register<Foo>(Reuse.Singleton); // !!! If the consumer of replaced dependency is singleton, it won't work
// cause the consumer singleton should be replaced too
c.UseInstance<IBar>(new Bar());
var foo = c.Resolve<Foo>();
Assert.IsInstanceOf<Bar>(foo.Bar);
c.UseInstance<IBar>(new Bar2());
var foo2 = c.Resolve<Foo>();
Assert.IsInstanceOf<Bar2>(foo2.Bar);
}
I am using Microsoft SignalR in order to push notification to browsers. Those notifications are triggered by action from other browsers. I want to make a background task which send notification sometimes. For example, at 12:45:21 i want to fire a notification to all connected users, even if they are doing nothing. Is it possible to do that ?
SignalR doesn't give you the ability to run a background task, but if you run are running a background task, there is nothing to stop your task using your SignalR hub to invoke client methods and send any desired notification.
To launch and control your background task, Hangfire is a flexible library that should help.
Edit to add: Since you've clarified you want to do this in a windows service, another prominent library to assist with building and deploying services is TopShelf
Edit to add: Also, I gather from your comment that you're trying to understand how to access the hub object from your background task? There are many ways to do this, but to improve testability and maintainability of your program, I recommend using an IoC (Inversion of Control) container, and injecting the necessary references - this tutorial: Dependency Injection in SignalR has a walkthrough using the Ninject library. That walkthrough is oriented towards asp.net hosting, but the link you found should help with adapting to a windows service.
If you are using asp.net core 2.1, this is now possible using BackgroundService/IHostedService
https://github.com/davidfowl/UT3/blob/fb12e182d42d2a5a902c1979ea0e91b66fe60607/UTT/Scavenger.cs#L9-L40
(Contents below)
public class Scavenger : BackgroundService
{
private readonly IHubContext<UTTHub> _hubContext;
private readonly ILogger<Scavenger> _logger;
public Scavenger(IHubContext<UTTHub> hubContext, ILogger<Scavenger> logger)
{
_hubContext = hubContext;
_logger = logger;
}
protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
while (!stoppingToken.IsCancellationRequested)
{
// Mark games that haven't played in a while as completed
var changed = Game.MarkExpiredGames();
// Mark completed games as removed
var removed = Game.RemoveCompletedGames();
if (removed > 0)
{
_logger.LogInformation("Removed {GameCount} games.", removed);
}
if (removed > 0 || changed)
{
await _hubContext.Clients.All.SendAsync("GameUpdated", Game.GetGames());
}
await Task.Delay(5000);
}
}
}
}
Also see this
https://github.com/aspnet/Docs/issues/8925
I have a requirement to start a process on the server that may run for several minutes, so I was thinking of exposing the following hub method:-
public async Task Start()
{
await Task.Run(() => _myService.Start());
}
There would also be a Stop() method that allows a client to stop the running process, probably via a cancellation token. I've also omitted code that prevents it from being started if already running, error handling, etc.
Additionally, the long-running process will be collecting data which it needs to periodically broadcast back to the client(s), so I was wondering about using an event - something like this:-
public async Task Start()
{
_myService.AfterDataCollected += AfterDataCollectedHandler;
await Task.Run(() => _myService.Start());
_myService.AfterDataCollected -= AfterDataCollectedHandler;
}
private void AfterDataCollectedHandler(object sender, MyDataEventArgs e)
{
Clients.All.SendData(e.Data);
}
Is this an acceptable solution or is there a "better" way?
You don't need to use SignalR to start the work, you can use the applications already existing framework / design / API for this and only use SignalR for the pub sub part.
I did this for my current customers project, a user starts a work and all tabs belonging to that user is updated using signalr, I used a out sun library called SignalR.EventAggregatorProxy to abstract the domain from SignalR. Disclaimer : I'm the author of said library
http://andersmalmgren.com/2014/05/27/client-server-event-aggregation-with-signalr/
edit: Using the .NET client your code would look something like this
public class MyViewModel : IHandle<WorkProgress>
{
public MyViewModel(IEventAggregator eventAggregator)
{
eventAggregator.Subscribe(this);
}
public void Handle(WorkProgress message)
{
//Act on work progress
}
}
I have an asp.net process which also consumes messages from a servicebus (MassTransit). For webrequests my database session is resolved with a PerWebRequest lifestyle.
But when the process consumes a message from MassTransit I need the database session to have another lifestyle, as no HttpContext is available.
I have made this:
public class PerRequestLifeStyleManager : ILifestyleManager
{
readonly PerWebRequestLifestyleManager perWebRequestLifestyleManager;
readonly PerThreadLifestyleManager perThreadLifestyleManager;
public PerRequestLifeStyleManager()
{
perWebRequestLifestyleManager = new PerWebRequestLifestyleManager();
perThreadLifestyleManager = new PerThreadLifestyleManager();
}
public void Init(IComponentActivator componentActivator, IKernel kernel, ComponentModel model)
{
perWebRequestLifestyleManager.Init(componentActivator, kernel, model);
perThreadLifestyleManager.Init(componentActivator, kernel, model);
}
public object Resolve(CreationContext context)
{
return GetManager().Resolve(context);
}
public bool Release(object instance)
{
return GetManager().Release(instance);
}
public void Dispose()
{
GetManager().Dispose();
}
ILifestyleManager GetManager()
{
if (HttpContext.Current != null)
{
return perWebRequestLifestyleManager;
}
return perThreadLifestyleManager;
}
}
Can anyone tell me, if this is the right way to go? And if it isn't, what is?
Thanks.
EDIT: I have just updated the question with some code that seems to work (before it was untested). I still am eager to know if this - seen from a Windsor perspective - is safe and sound.
Try using one of the hybrid lifestyles.
By using the Castle Windsor extension, you should just be able to have your ISession as a dependency on the constructor of the consumer class. That way, the container will manage the lifecycle of the ISession, and dispose of it once the consumer is disposed by MT.
If you need even more control, you can look at how the WindsorConsumerFactory is implemented to wrap the resolution and release of the consumer class instance around the delivery of the message to the consumer.
If you need to inject something beyond that, you can also use an interceptor:
Unit of work when using MassTransit