How to Use PRG Pattern with ASP.net MVC

What is the PRG Pattern ?

• PRG stands for "Post/Redirect/Get"
• Instead of returning an HTML page directly,
• The POST operation returns a redirection command (using the HTTP 303 response code (sometimes 302) together with the HTTP "Location" response header),
• Instructing the browser to load a different page using an HTTP GET request
• The result page can then safely be bookmarked or reloaded without unexpected side effects

How to Explain this by using an Example ?

• Here I'm going to use User Registration function as an example
• If the Registration attempt is Successful, the user should be redirected to his Home page
• Otherwise they should be redirected back to the Registration page

Image 1 : Shows Action Methods Interaction When do Registration

AccountController.cs        

        

Code for the Register Action Method (Get) for Displaying Register View is as below

        /// <summary>

        /// for displaying Register View

        /// </summary>

        [HttpGet]

        [AllowAnonymous]

        public ActionResult Register()

        {

            return View();
              }

      Image 2 : Register View

        

Code for the Register Action Method (Post) for Processing the Registration and Shows Register Page again is as below

        /// <summary>

        /// for Registering the User

        /// </summary>

        [HttpPost]

        [AllowAnonymous]

        [ValidateAntiForgeryToken]

        public ActionResult Register(RegisterModel model)

        {

          if (ModelState.IsValid)

          {

            // Attempt to register the user

            try

             {

               WebSecurity.CreateUserAndAccount(model.UserName, model.Password);

               WebSecurity.Login(model.UserName, model.Password);

               ViewBag.Message = "Successfully Registered!";

               return View(model);//PRG has not been Maintained

             }

              catch (MembershipCreateUserException e)

             {

                 ModelState.AddModelError("", ErrorCodeToString(e.StatusCode));

             }

          }

            // If we got this far, something failed, redisplay form

            return View(model);

        }

    Image 3 : New user has been Created

        

• At this point If you try to Refresh (F5) or Reload the Page,You'll see below mentioned kind ofSecurity Alert Message Box

      Image 4 : Register form with "Confirm Form Resubmission" Message Box

        

• After that If you try to press "Continue" Button, You'll see below mentioned Run time exception
• But for another situation this may be Data Duplication issue etc.

      Image 5 : Run time Exception

How to Get Rid Of this Issue ?

• You have to maintain PRG Pattern with your Return type, After finishing the SuccessfulRegistration
• To properly perform PRG you must return a redirecting ViewResult from your Action
• Such as RedirectToAction, otherwise you'll get the dialog box pictured above (i.e. Image 4)

Code for the Properly Perform PRG Pattern is Maintaining Register Action Method is as below

    /// <summary>

    /// for Registering the User

    /// </summary>

    [HttpPost]

    [AllowAnonymous]

    [ValidateAntiForgeryToken]

    public ActionResult Register(RegisterModel model)

     {

      if (ModelState.IsValid)

      {

       // Attempt to register the user

       try

       {

         WebSecurity.CreateUserAndAccount(model.UserName, model.Password);

         WebSecurity.Login(model.UserName, model.Password);

         

         return RedirectToAction("Index", "Home");//PRG has been Maintained

        }

        catch (MembershipCreateUserException e)

        {

          ModelState.AddModelError("", ErrorCodeToString(e.StatusCode));

        }

      }

       // If we got this far, something failed, redisplay form

       return View(model);

     }

       Image 6 : Home page

That's It.You're Done.