Building Data-Driven Web Apps with Flask and SQLAlchemy Transcripts
Chapter: Client and server-side validation
Lecture: Server-side validation with Viewmodels
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The second core service that view models provide
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to our application is server side validation.
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So we've set all of these fields here in our initialization.
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This is the data exchange
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but sometimes, not all the time, sometimes
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we need to validate it.
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If we're just getting, doing a standard get
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and showing the data, there's rarely a validation
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but if we're working with forms in the post side of things
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then we do want to validate that.
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We could do that in the view method
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but it's going to get all messy and why would we do it there?
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We're going to move it down to a validate method.
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So here, we're going to say if the first name is not set
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or the last name is not set
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we'll give an error, like hey you have to specify a name
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or an email is not right, you got to specify an email.
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Same for the password.
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We saw lots of interesting validation that we could do here.
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You can imagine we could make this nicer, right?
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Regular expressions on emails and so on.
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We also could see that we did richer types of validation
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not just here's a required field, but we go to the database
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and we say, someone's trying to register with this email
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to somebody already exists
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who has registered with that email.
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Remember there's a uniqueness constraint
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and it's going to actually be some kind of error
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if we try to save it theoretically
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and we want to give them a friendly message
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instead of a crash that says hey that didn't work
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for whatever reason.
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So we can tell them really nicely
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hey that user with that email already exists.
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And even suggest, would you like to try to log in
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or reset your password?
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If you're trying to register, maybe you forgot
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what your account is. Things like that.
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So there's validation, it's really, really nice.
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What's cool about it is, we can add tons of validation here
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and it doesn't make our view method any more complicated.
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This validate method just bundles it all up
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and it's great, right here.