Building data-driven web apps with Pyramid and SQLAlchemy Transcripts
Chapter: Client and server-side validation
Lecture: Client-side validation with HTML5
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View models are awesome for validating server-side code
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but me might as well do as much validation as we can
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in the browser before it ever touches our server
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before it ever even leaves the browser
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in the form of a request.
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This won't allow us to entirely skip server-side validation
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cuz people could always turn that kind of stuff off
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use scripts and so on and get around it
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but at least it will give our users
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a slightly better experience.
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So let's go back to our PyPI validation
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version of our demo code
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and let's add some client-side validation.
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First of all, let's just run it and see where we are
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so let's go try to register.
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Now, if I put "abc" here, and I hit Go
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notice you'll see a little flicker
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and then a message comes down here
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and this is actually ridiculously fast, like it's
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if we look at what's happening
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this is in less than a millisecond, pretty incredible.
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That's cuz there's zero milliseconds being timed
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between me and the server, right?
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If we're halfway round the world
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that could be much, much longer.
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Either way, this is going back and hitting my web server.
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It'd be nice if it'd just, as users type, it would say
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"This is valid, this is invalid," and so on.
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So, let's go and change that so as much as possible
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this will validate on the client side
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turns out it's super easy.
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Over here, in Register, we have this form, right?
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Let's go way to the end here, and on this form
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we can come over here and say Your Name
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you know what that is, Required
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we don't even have to set a value
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just put the attribute of Required on them.
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The other thing we did is we set
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the type to be various things.
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Here we set the Type of e-mail to be text
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but we can upgrade it to be of type email
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or number, or things like that.
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Now, if we just save, we can come over here and refresh.
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Let's refresh like this, and if we hit Go
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notice no POST back, and here it says
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"Please fill out this field."
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Okay, so Michael, great, and I hit this.
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Okay, whatever, I don't care.
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It says, "No, no, no, e-mail address."
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C'mon Michael that's michael@talkpython.fm
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yeah, sure give it a password
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and then I'm going to go over here and go
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It does appear that we're missing
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a little validation there, doesn't it
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cuz it let that submit
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but let's also fix that really quick.
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Where do we do validation?
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We saw we do that in our view model
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so we can go to our user_service
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and say, find_user_by_email.
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It doesn't exist, but it will in a second.
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Write that really quick.
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You know what, it's so much like that
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but here we just say, email and that's going to be email.
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We can say that's a string, and what we get back
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an optional of user. Now, let's try one more time.
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Log out and try to register one more time with that.
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Boom, this user already exists, so notice
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if this is missing altogether, it never even goes back
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there's no flicker up here, it never goes there.
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Let's actually load it up fresh.
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Okay, so when I click it, it never goes back
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but if I fill this out and then I hit it
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you'll see it flicker and it falls back
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to the server-side validation cuz the client-side
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we're not really checking.
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We're not going to access the database through java script.
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We're just going to let the server do that
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so there you can see that's going back to the server
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once it passes client-side validation
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so it's not all or nothing on client server
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it's this blend much of the time.
