ContactController.cs

namespace ContactList.Features.Contact
{
    using System.Web.Mvc;
    using MediatR;

    public class ContactController : Controller
    {
        private readonly IMediator _mediator;

        public ContactController(IMediator mediator)
        {
            _mediator = mediator;
        }

        //other actions...

        public ActionResult Edit(ContactEdit.Query query)
        {
            var model = _mediator.Send(query);

            return View(model);
        }

        [HttpPost]
        public ActionResult Edit(ContactEdit.Command command)
        {
            if (ModelState.IsValid)
            {
                _mediator.Send(command);

                return RedirectToAction("Index");
            }

            return View(command);
        }
    }
}