3. Controllers, actions and action results

public class ProductsController : Controller
{
    private readonly IProductService _products;
    public ProductsController(IProductService products) => _products = products;    // needs a DI container in MVC 5

    public ActionResult Index(string q, int page = 1) => View(_products.Search(q, page));

    public ActionResult Details(int id)
    {
        var p = _products.Get(id);
        if (p == null) return HttpNotFound();
        return View(p);
    }

    [HttpGet] public ActionResult Create() => View(new ProductEditModel());

    [HttpPost, ValidateAntiForgeryToken]
    public ActionResult Create(ProductEditModel model)
    {
        if (!ModelState.IsValid) return View(model);           // redisplay with validation messages
        _products.Add(model);
        TempData["Message"] = "Product created";
        return RedirectToAction(nameof(Index));                // Post-Redirect-Get pattern
    }

    public async Task<ActionResult> Export() => File(await _products.ExportCsvAsync(), "text/csv", "products.csv");
    public JsonResult Lookup(string term) => Json(_products.Lookup(term), JsonRequestBehavior.AllowGet);
}