C#•4mo ago

How to avoid the Service Locator anti pattern when needing to instantiate multiple of a DI instance?

I have a Typed Client (Service Agent) as per https://learn.microsoft.com/en-us/aspnet/core/fundamentals/http-requests?view=aspnetcore-8.0#typed-clients, and it is consumed in a class as a ctor DI, but I need to instantiate a new instance per request.† So instead I currently use a Service Locator, which is an anti pattern, and thus I'd like to avoid this. I'm not sure how a factory would solve it, since then I'd just move the DI instantiating problem to the factory. Code example of what I have:

public class MyService
{
  public MyService(HttpClient httpClient)
  {
    // ....
  }

  public async Task<Whatever> MyEndpoint()
  {
    return await _httpClient //...
  }
}

public class MyConsumer<T> where T : class
{
    public MyConsumer(IServiceProvider serviceProvider)
    {
      // ...
    }

    public async Task<Foobar> PerformMultipleRequests()
    {
      //some loop
      var myService = _serviceProvider.GetRequiredService<T>();
      myService.MyEndpoint()
      // ...
    }
}

public class MyService
{
  public MyService(HttpClient httpClient)
  {
    // ....
  }

  public async Task<Whatever> MyEndpoint()
  {
    return await _httpClient //...
  }
}

public class MyConsumer<T> where T : class
{
    public MyConsumer(IServiceProvider serviceProvider)
    {
      // ...
    }

    public async Task<Foobar> PerformMultipleRequests()
    {
      //some loop
      var myService = _serviceProvider.GetRequiredService<T>();
      myService.MyEndpoint()
      // ...
    }
}

† The reason I need to spawn a client / service per request, is that the endpoint I'm writing against doesn't accept multiple simultaneous requests from the same client. Right now I'm just building around it but hopefully it'll get fixed

22 Replies

Tvde1•4mo ago

Why does the limitation of the external API make it so you need to create a scope? I can imagine you'd want your MyService to be a Singleton, to manage that there will only be one concurrent request

frobnicate•4mo ago

Because I need multiple requests to run in parrallel, and the external API does not allow multiple concurrent requests from the same client

Tvde1•4mo ago

What do you mean "from the same client"? is it a HTTP call and identified by a header or user agent?

frobnicate•4mo ago

In practice, when I use the same instance of a HttpClient, to do multiple requests on the API, it will fail. If I make a HttpClient per request, it works. I'm not sure why It's a different company that makes the external API and they haven't documented it :catshrug:

Tvde1•4mo ago

just curious, how do you notice it fails? Do you get a certain response?

frobnicate•4mo ago

500

Tvde1•4mo ago

oopsie I think I'd make MyService a transient/scoped, and it'll get a IHttpClientFactory that way, MyConsumer can rely on MyService to do the right logic you want this weird behavior to be in your MyService such that if it ever changes, you change the single part responsible for it

frobnicate•4mo ago

So MyService has a ctor DI IHttpClientFactory?

Tvde1•4mo ago

yes

Tvde1•4mo ago

https://learn.microsoft.com/en-us/dotnet/core/extensions/httpclient-factory

Use the IHttpClientFactory - .NET

Learn how to use the HttpClient and IHttpClientFactory implementations with dependency injection in your .NET workloads.

frobnicate•4mo ago

I had hoped I could do it with typed clients :c Oh well

Tvde1•4mo ago

I don't really get the point of typed clients, but that might just be me