HttpContext.RequestServices.GetService<T>() vs services.AddScope<T>()?
The difference is that you don't need to inject IMediator
to the constructor of BaseController and to all sub classes of BaseController.
So it's saves some boilerplate, but also makes the dependency less explicit.
Side note, Microsoft recommends to prefer the injection over RequestServices
The services available within an ASP.NET Core request from HttpContext are exposed through the HttpContext.RequestServices collection.
Request Services represent the services configured and requested as part of the app. When the objects specify dependencies, these are satisfied by the types found in RequestServices, not ApplicationServices.
Generally, the app shouldn't use these properties directly. Instead, request the types that classes require via class constructors and allow the framework inject the dependencies. This yields classes that are easier to test.
Note
Prefer requesting dependencies as constructor parameters to accessing the RequestServices collection.
See Microsoft docs
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ca9163d9
Updated on July 28, 2022Comments
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ca9163d9 almost 2 years
In the following code (from https://github.com/JasonGT/NorthwindTraders/blob/master/Src/WebUI/Controllers/BaseController.cs), it's a base control inherited by all controllers.
[ApiController] [Route("api/[controller]/[action]")] public abstract class BaseController : ControllerBase { private IMediator _mediator; protected IMediator Mediator => _mediator ??= HttpContext.RequestServices.GetService<IMediator>(); }
The sub-class controllers then just use the property of
Mediator
.How it differs from just adding
services.AddScope<Mediator>();
inStartup.cs
and then injectmediator
.// Startup.cs public void ConfigureServices(IServiceCollection services) { // services.AddSingleton<Mediator>(); services.AddScope<Mediator>();
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JohanP over 4 yearsIn the
BaseController
, nothing is getting injected for it has no ctor.IMediator
needs to get initialized when it is null, so what is done there is Service Locator pattern instead of injecting. You would still needservices.AddScope<Mediator>();
for it to work tho.
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