Building data-driven web apps with Pyramid and SQLAlchemy Transcripts
Chapter: User input and HTML forms
Lecture: GET-POST-Redirect pattern
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Now before we write some code
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let's talk a little bit about the flow
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that people go through when they're working with forms.
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There's many ways to do this
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but there's one pattern that really helps
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both organize your server side code
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and prevent that annoying warning like
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"are you sure you want to refresh this page?
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"You've posted it, it might resubmit
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"your purchase request" or whatever.
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I'm calling this the Get Post Redirect pattern.
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So what's that look like?
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Well, we have of course our server.
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Our server has some sort of data.
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We have a web browser, and our web browser
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is going to interact with our site.
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It's going to say, "Hey, I want to view this HTML page
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"that happens to have a form
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"like I want to register for your site."
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And then over here locally, they're like
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"All right, great.
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"Here's my username, here's my password, my name,"
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whatever you got to do to register.
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They type that in and they click that submit button
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we just talked about.
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That posts all that data back
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and they're like, "Great, we've got a new account.
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"We want to create it, we're going to save that to the database."
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Now we're going to tell the browser to move over
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to another page, redirect, send a temporary redirect
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302 over to /welcome, and welcome to the site.
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That way, if they bookmark it
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or they refresh it or whatever
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they're going to end up on welcome
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having already created it not being left on the same URL
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where a POST just happened.
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Like I said, if you refreshed that
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you would get a warning saying
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"Hey, this page is going to resubmit
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"Are you sure you want to do that?"
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So this Get Post Redirect pattern is super common
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and it's really nice on the server side.
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I'll show you how to break that out
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into different methods nice and easy
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so one handles the get, one handles the post.
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So one handles the show the form
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pre-populated with starter data.
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The other processes that input
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and keeps the code really clean.
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You don't have to test whether it's being submitted or not.
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This common pattern is sometimes known
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under a different name, the Post Redirect Get pattern.
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So over here on Wikipedia, they have an article on it.
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You can read more about it as you want.
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To me, you have to start from somewhere
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and you start from the get, and then you do the post
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and then you do the redirect.
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That's the life cycle of that form interaction.
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So I think that's why I call it Get Post Redirect
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but Wikipedia, they have a different name.
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It's fine. It's a pretty common pattern
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and you can get more information about it here.
