#100DaysOfWeb in Python Transcripts
Chapter: Days 81-84: Unit testing web apps
Lecture: Concept: View models
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Before we go on to testing. Let's quickly review this concept of a ViewModel. So this is a pattern that I borrowed from other places
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but I think makes a lot of sense on web applications. The idea is, typically, this is most useful when you have forms and some user data
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but it also works when there's just straight GETs. So in this case we have a HTML form and it's going to submit some data
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to register the user on the site. Traditionally the way web applications might be written is there's one huge, long view
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or action method that has to do all the work. And it's all crammed in there, all the validation all the data exchange, everything.
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And that makes it hard to see what's actually happening. And actually test that separately from all the things going on around it
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instead what we're going to do is we're going to exchange this one huge method doing all the stuff with a couple of pieces
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of code that do more single responsibility-style programing. One core thing. So let's change this up a little bit.
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Make a smaller viewer action method in the ViewModel that does this data exchange invalidation. And then the action method
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is just going to work with the ViewModel. So where's the value? Well you'll see that our code we write
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in this case the register method, is much simpler. The GET one is incredibly simple. So we just call this two dictionary and in the POST we'll create
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our registration ViewModel's case. Do some validation from the form. Check to see whether there's an error.
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The data that gets exchanged, it's always consistent. Cause this to_dict always returns the same thing that can cause an error if you omit a key
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from a dictionary, for example. And then we can just check. Just do the simple code we're suppose to do. Are they registered? Yes or no. Did that work?
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Yes or no. If it didn't we're going to need to set an error and return that. Otherwise we just take them on to where they were going.
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Alright take them to the homepage. Great, you're logged in now. So as you can see this would be much more complicated with lots
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of reading and converting values out of dictionaries and checking that they exist and things like that. But all of that has been moved
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over to this registration ViewModel. It's beautiful.