Hellooo….. Today post I will talk about what is PRG in ASP.NET MVC 4 and how to use it. Before we start, the question is what is PRG?

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 of Security 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 Successful Registration
• 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);
         ViewBag.Message = "Successfully Registered!";
         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

DONE!!