What should be the namespace used in ASP.NET Core Web API?

Question

In my ASP.NET Core Web API project, I want to use methods like HttpPost , HttpGet , HttpDelete . When I've added that onto the action, IntelliSense suggests these three namespaces:

System.Web.Mvc 
System.Web.Http
Microsoft.AspNetCore.Mvc

Which one should be used and why?

Answer 1

Microsoft.AspNet.Mvc and System.Web.Mvc are exactly the same if you have View support, then use Mvc, This will support Mvc Design pattern

if not (you are simply calling third party apps) then use System.Web.Http

Take a look at this => What is the different between System.Web.Http.HttpPut Vs System.Web.Mvc.HttpPut

and this => For MVC 4, what's the difference between Microsoft.AspNet.Mvc and System.Web.Mvc?

Answer 2

The Microsoft.AspNetCore.Mvc is the default namespace when you create an Asp.NET Core Web API in VisualStudio. There is no need to depend on your project on other namespaces.
You can also read this document:
https://docs.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.mvc?view=aspnetcore-5.0

for example :

using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace CoreWebApi.Controllers
{
    [ApiController]
    [Route("[controller]")]
    public class WeatherForecastController : ControllerBase
    {
        private static readonly string[] Summaries = new[]
        {
            "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
        };

        private readonly ILogger<WeatherForecastController> _logger;

        public WeatherForecastController(ILogger<WeatherForecastController> logger)
        {
            _logger = logger;
        }

        [HttpGet]
        public IEnumerable<WeatherForecast> Get()
        {
            var rng = new Random();
            return Enumerable.Range(1, 5).Select(index => new WeatherForecast
            {
                Date = DateTime.Now.AddDays(index),
                TemperatureC = rng.Next(-20, 55),
                Summary = Summaries[rng.Next(Summaries.Length)]
            })
            .ToArray();
        }
    }
}