Building Data-Driven Web Apps with Pyramid and SQLAlchemy Transcripts
Chapter: User input and HTML forms
Lecture: GET-POST-Redirect pattern
Login or
purchase this course
to watch this video and the rest of the course contents.
0:00
Now before we write some code
0:01
let's talk a little bit about the flow
0:03
that people go through when they're working with forms.
0:05
There's many ways to do this
0:07
but there's one pattern that really helps
0:09
both organize your server side code
0:11
and prevent that annoying warning like
0:14
"are you sure you want to refresh this page?
0:17
"You've posted it, it might resubmit
0:19
"your purchase request" or whatever.
0:22
I'm calling this the Get Post Redirect pattern.
0:26
So what's that look like?
0:27
Well, we have of course our server.
0:30
Our server has some sort of data.
0:31
We have a web browser, and our web browser
0:33
is going to interact with our site.
0:35
It's going to say, "Hey, I want to view this HTML page
0:37
"that happens to have a form
0:38
"like I want to register for your site."
0:41
And then over here locally, they're like
0:42
"All right, great.
0:43
"Here's my username, here's my password, my name,"
0:47
whatever you got to do to register.
0:49
They type that in and they click that submit button
0:52
we just talked about.
0:53
That posts all that data back
0:55
and they're like, "Great, we've got a new account.
0:56
"We want to create it, we're going to save that to the database."
0:58
Now we're going to tell the browser to move over
1:02
to another page, redirect, send a temporary redirect
1:06
302 over to /welcome, and welcome to the site.
1:10
That way, if they bookmark it
1:12
or they refresh it or whatever
1:14
they're going to end up on welcome
1:16
having already created it not being left on the same URL
1:21
where a POST just happened.
1:22
Like I said, if you refreshed that
1:24
you would get a warning saying
1:26
"Hey, this page is going to resubmit
1:27
"Are you sure you want to do that?"
1:29
So this Get Post Redirect pattern is super common
1:32
and it's really nice on the server side.
1:35
I'll show you how to break that out
1:36
into different methods nice and easy
1:38
so one handles the get, one handles the post.
1:42
So one handles the show the form
1:45
pre-populated with starter data.
1:46
The other processes that input
1:48
and keeps the code really clean.
1:49
You don't have to test whether it's being submitted or not.
1:52
This common pattern is sometimes known
1:54
under a different name, the Post Redirect Get pattern.
1:59
So over here on Wikipedia, they have an article on it.
2:02
You can read more about it as you want.
2:04
To me, you have to start from somewhere
2:06
and you start from the get, and then you do the post
2:10
and then you do the redirect.
2:11
That's the life cycle of that form interaction.
2:14
So I think that's why I call it Get Post Redirect
2:16
but Wikipedia, they have a different name.
2:19
It's fine. It's a pretty common pattern
2:21
and you can get more information about it here.
