The PRG pattern is a valuable way of handling your user experience after a form post, even when you aren’t using the ASP.NET MVC framework.

There are quite a few articles online that blindly redirect whether or not the model state is valid, but this is not necessary. The cleanest and simplest way to handle an invalid post is to re-display the view. This then negates the need to pass around data as it already available directly.

Although one reason to use the post-redirect-get pattern is to avoid the “Are you sure you wish to re-submit this form” warning, another reason is that if the user mistakenly confirms a second submission you have to consider the impact of the second submission on your data. If the original post was invalid, a re-submission will not pose a risk to your data integrity.

Keep up the great work on your blog.

However not doing a redirect on invalid state, as the article mentions, is very useful for avoiding use of tempdata and sessionstate, and thus being able to scale out more easily.

To make returning a view from your POST action as easy as possible make sure you create your view model in a separate mapper for maximum reuse. I so often see a lot of logic repeated in both controller actions, while this is totally unnecessary. Always keep DRY (don’t repeat yourself) in mind.

Here it says that on an error, the PRG pattern does not require you to return a GET action. You’re only required to return a GET when any data has changed.

The pattern does prevent repeating the form post, once you are redirected and use the back button.