Building Data-Driven Web Apps with Flask and SQLAlchemy Transcripts
Chapter: Client and server-side validation
Lecture: Concept: Viewmodel
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You've seen view models in action
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let's review them as a general concept.
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So here's a mock up of a web browser
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some sort of architectural view of our server
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and the user of the web browser submitting a form.
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Here they're doing their HTTP POST
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for the register action form page.
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And they're submitting some form data
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which we didn't elaborate too much on here
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but you see some sort of form data is being submitted.
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Now, the way that Flask encourages you to handle this
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in general, and a lot of the web framers do
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is to just have some super complicated view method.
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Why? Well, there's no other pattern to tell you
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it doesn't have to be that way
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cause you have to do all the data acquisition
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the data normalization like stripping
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and lower-casing the email, stuff like that.
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You've got to do the validation
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you've got to do lots of testing
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like does this user already exist?
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Typically, here's the function where you do that.
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Go to town, sorry it's 200 lines.
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All right, things like that.
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But it doesn't have to be that way.
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We saw the view model pattern takes the data exchange
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the data normalization, and the data validation
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and it pushes it somewhere else
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that can be tested separately, maintained separately.
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And our view method only has to process the essence.
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It gets the data, maybe it creates the user
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and it doesn't redirect, or something to that effect.
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Sends them a welcome email, things like this.
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So we can exchange this yellow box
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for a much smaller, more maintainable version
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and instead of writing all that validation
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and exchange data, we create a view model
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and we just work with that view model over here.
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Now this is the general idea
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of this view model design pattern.
