Building data-driven web apps with Flask and SQLAlchemy Transcripts
Chapter: Client and server-side validation
Lecture: Using a viewmodel

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0:00 Now with this view model base in place
0:03 let's go and actually see how we might use it.
0:06 This is what is actually calling for
0:09 the view model idea the most.
0:10 But let's start with something simpler.
0:12 Just this index, like all we want to do
0:14 is simply show the user details on the screen.
0:18 So we've got to get the user_id
0:19 and potentially, the user as well.
0:21 So, let's go over here to the account
0:23 and we'll have a index view model, something like that.
0:27 We could call it AccountIndexViewModel
0:30 but I'll leave it up to you how you want to name these.
0:33 And it turns out to be really straightforward, what we need.
0:36 We'll come over here and say IndexViewModel.
0:40 And it's going to derive from ViewModelBase.
0:42 So let's import that.
0:44 And actually, I'd like to name it slightly differently.
0:52 Something like that, so it doesn't conflict
0:53 with our class name which what we actually care about.
0:56 So we're going to have another initializer here
0:59 and it's not actually going to take any arguments
1:02 'cause we're not getting any arguments here
1:04 or anything like this.
1:06 So we're going to come down there
1:07 and the first thing we have to do is
1:08 PyCharm miscellaneous
1:09 add a call to super so it'll write this
1:11 or we could write it ourselves.
1:14 And then, let's look at what we're exchanging.
1:16 Well, this part right here we
1:18 have to get an exchange for that
1:20 and that's actually happening already.
1:22 We also have to go over and get the user.
1:25 So let's try that.
1:27 We'll come over here to our IndexViewModel
1:28 and well say self.user is user_service
1:31 got to import that.
1:33 What do we pass here?
1:34 Remember the base class is already setting that up
1:36 and that happened already there
1:38 so we'll say self.user_id, super!
1:41 And this may or may not come through
1:44 Now what else do we have to do?
1:45 Let's actually go back and find out.
1:48 So we're going to go over here and create a vm
1:50 which is a IndexViewModel, like so.
1:56 Create one of these.
1:57 Now this already happens, and so does this.
2:00 So all we have to do is go down here
2:02 and say vm.user and let's go ahead
2:04 and check that actually the query went down to the database
2:06 and found a real user, 'cause maybe somehow
2:10 they deleted their account or whatever.
2:12 All right, if we can't actually get a user
2:13 from the database they have to go login.
2:16 Look how that got simpler, that's nice.
2:18 Now remember, over here we had to do this as well.
2:21 Now what do we return?
2:22 All the fields and stuff contained within this view model.
2:26 There is this extra error thing
2:28 but it doesn't matter, we're just going to not use it
2:30 and we'll just say to_dict, and that's it!
2:33 Look how much cleaner this is become.
2:36 And as we add more information to be exchanged
2:39 this part here gets no more complicated.
2:42 It's this data exchange bit, and this is pretty simple
2:45 but we're going to get more interesting stuff
2:47 as we move down the line here in this file.
2:50 But already this has gotten better.
2:51 Well, I say it gets better, it's actually going to be better
2:54 if it really continue to work but have a better style serve.
2:59 All right, it looks like it restarted.
3:00 Let's go and see that it still works.
3:02 All right we're still logged in, ta-da!
3:05 There we go, so we got up here, the user_id info
3:08 we got here, the actual user object
3:10 and then we pass some other information
3:12 that we technically don't need.
3:14 Cool, huh?
3:15 So here's a simple version of using a view model.