Is ApiController deprecated in .NET Core

Update ASP.NET Core 2.1

Since ASP.NET Core 2.1 a new set of types is available to create Web API controllers. You can annotate your controllers with the [ApiController] attribute which enables a few new features such as automatic model state validation and binding source parameter inference. See the docs for more information: https://docs.microsoft.com/en-us/aspnet/core/web-api/index?view=aspnetcore-2.1#annotate-class-with-apicontrollerattribute.

There is indeed no particular ApiController class anymore since MVC and WebAPI have been merged in ASP.NET Core. However, the Controller class of MVC brings in a bunch of features you probably won't need when developing just a Web API, such as a views and model binding.

You've got two options if you want something different:

Use the ControllerBase class in the Microsoft.AspNetCore.Mvc.Core package.

Or

Create your ApiController base class. The key here is to add the [ActionContext] attribute which injects the current ActionContext instance into the property:

[Controller]
public abstract class ApiController
{
    [ActionContext]
    public ActionContext ActionContext { get; set; }
}

Also, add the [Controller] attribute to the class to mark it as a controller for the MVC controller discovery.

See more details in my “Web API in MVC 6” blogpost.

The [ApiController] attribute actually got added back in ASP.NET Core version 2.1.

Features coupled with the attribute are:

• Validation errors automatically trigger an HTTP 400 response.
• No more need to define [FromBody], [FromRoute], ... attributes explicitly

Links to the docs:

• https://docs.microsoft.com/en-us/aspnet/core/aspnetcore-2.1?view=aspnetcore-2.1#apicontroller-actionresult
• https://docs.microsoft.com/en-us/aspnet/core/web-api/index?view=aspnetcore-2.1#annotate-class-with-apicontrollerattribute

Update

There is also the baseclass ControllerBase for controllers to inherit from which is suited for api-controllers because it ommits all view-related functionality.

• https://docs.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.mvc.controllerbase?view=aspnetcore-2.1

In ASP.NET core uses terms and concepts known from ASP.NET MVC and ASP.NET WepAPI. But basically it is a complete new framework. Therefore there are several concepts or base classes that we can simply forget.

ASP.NET MVC and ASP.NET WebApi are two coexisting but different frameworks and therefore a destinction has to be made to specify a controller as a WebApi Controller by using the ApiController as base class.

In ASP.NET Core this is simply not necessary anymore. The Controller base class can be used for actions that return HTML from Razor Views or JSON (with output formatters XML and other formats are possible as well). You don't even need the Controller base class. It is even possible to use a "Plain Old C# Object" as Controller without inheritence.

Below is an example of a Demo-Controller to outline, that even though the ApiController is not there, the structural approach to deliver data to the client is similar.

public class DemoController : Controller
{       
     public async Task<IActionResult> Action()
     {
         var model = await _someService.GetPreciousData();
         return Ok(model);
     }
 }