Question

Is there any best practice for PRG pattern with MVC?
In this tutorial:
http://www.theserverside.com/news/1365146/Redirect-After-Post
the proposed solution requires 4 actions:
Create_Item (POST) => “resets” the form and redirects to Display_Item
Display_Item (GET) => shows the form (with temp data and errors if exists)
Store_Item (POST) => try to save data to DB, if errors, save errors and redirect to Display_Item, if success redirect to Display_Stored
Display_Stored (GET) => shows the item created or a success message, tec.

Now, I think that to have the first action with POST is a problem, because we can’t start the form with a link. Using GET in Create_Item seems a better option.

And also, we can do the same with 3 actions (using the same action for Create_Item and Display_Item, but with an extra flag for reseting the form, for example:
http://www.example.com/controller/Create_Item/?reset=1

And also we can do the same with just 2 actions, because we can use an if inside Create_Item for checking if the request is GET or POST (so we are combining Display_Item with Store_Item).

And also we can do the same with just 1 action, because we can have an extra flag (in the URL query or in a session) for showing the results instead of the form:
GET http://www.example.com/controller/Create_Item/?reset=1 => shows a new form and redirects to the next URL
GET http://www.example.com/controller/Create_Item/ => shows a form with temp data and errors if exists
POST http://www.example.com/controller/Create_Item/ => save errors in temp, or data in DB (and set a session flag for success) and redirects to above URL or next URL
GET http://www.example.com/controller/Create_Item/ => if $_SESSION[‘success’] show results

Personally I like the idea of having 4 actions, but I don’t have any real advantage over the others options. But I don’t feel secure choosing my design without a real criteria.
Does somebody know the PROS and CONS of each design (if any)?

For example, I see the 4 actions cleaner, but if we want to change how the temp data is saved, we need to change it in 4 places.

Thanks!

Answer 1

The pattern is to GET a blank form, modify the contents of the form, then POST that to the server, which then sends a redirect to another page which is a GET, perhaps to a page saying Form submitted successfully.. (Get->)Post->Redirect->Get

The first action is not really POST. That’s the end result of completing a form and submitting it. The guide is more about what to do after that POST, as if you do not do a redirect, then the user is left on a page saying Form submitted successfully where they could just hit F5 and do another POST. With that redirect however, they’re on that results page via a safe GET which will not result in a double post.

As for the implementation, you should have each be its own action on the server side. This is inline with the MVC / RESTful implementation.

• GET /url?action=new -> Call new_form() method to render a new form
• POST /url?action=create -> Call create_form() method to save and redirect to /url?action=show&id=1234
• GET /url?action=show&id=1234 -> Call show_form() method to display the result
• POST /url?action=save&id=1234 -> Call save_form() method to save and redirect

You could use 3 actions here instead if you wanted to have the 2nd action call save. Most REST/CRUD conventions use the 4, but the choice is yours. The benefits are the same as going the REST/MVC route in the first place.

See these resources as well:

• RESTful web services
• This covers typical conventions for RESTful controllers. It covers rails, but still applies to PHP as well if you’re wanting to go the REST route.