How do I get a dependency needed in one method only, using ASP.NET Core

Question

I've registered my FooBar type with ASP.NET's built-in container.

I need an instance in one of my action methods. If I needed it in all of the controller's actions, then I'd inject it into the constructor. But I only need it in one action method.

So in the action method, I assume I could do this (untested):

var service = HttpContext.RequestServices.GetService(typeof(FooService)) as FooService;

But the docs say that is is a bad idea. I agree.

So what are my options?

Then this method is good candidate to move it to the own controller. And pass dependency through constructor — Fabio
– Fabio, Commented Nov 15, 2016 at 7:37
Then what is wrong with passing dependency through constructor of current controller if you stricted to use only one controller — Fabio
– Fabio, Commented Nov 15, 2016 at 7:39
Dependencies can be passed to the instance in three ways(what I know at this moment) constructor, method and property. In case of ASP.NET method and property not easy approach so you have only constructor. For example if you make dependency a public property then you can set it in middle-ware only for this method - but this makes your code more complex to maintain — Fabio
– Fabio, Commented Nov 15, 2016 at 7:46
@Fabio Okay that's what I needed to know. I can't find proper documentation for ASP.NET Core container. They only talk about constructor injection. I hope there is a simple way to do non-constructor way. — grokky
– grokky, Commented Nov 15, 2016 at 7:53

adem caglin · Accepted Answer · 2016-11-15 08:10:44Z

5

You can use FromServices attribute to inject a dependency into an action:

public IActionResult SampleAction([FromServices]FooService fooService)
{
   // ...
}

Sometimes you don't need a service for more than one action within your controller. In this case, it may make sense to inject the service as a parameter to the action method. This is done by marking the parameter with the attribute [FromServices] as shown here:

See official docs: https://learn.microsoft.com/en-us/aspnet/core/mvc/controllers/dependency-injection#action-injection-with-fromservices

answered Nov 15, 2016 at 8:10

adem caglin

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1 Comment

grokky Over a year ago

They upgraded the docs site, so I missed that! Thanks! This is exactly what I needed.

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