Building Data-Driven Web Apps with Flask and SQLAlchemy Transcripts
Chapter: MongoDB edition
Lecture: Home page cleanup
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0:00
It looks like our web app's working
0:02
but if we run it after we've imported data
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let's see what we get.
0:06
It's not going to be as fun as you might think.
0:09
No, that's not so good.
0:12
Remember we had a relationship on our releases package
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our releases object in SQLAlchemy
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that you go back to the package
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and we had done a join
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and you know we don't have this relationship
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we could set up something in that style, in MongoDB
0:28
but it's probably not the best practice
0:29
we don't have loading and things like that.
0:31
So what we're going to do is just change how we're doing this.
0:34
So lets see what is the problem.
0:37
The problem is actually down in the template here.
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So if we go to the home to the index
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you can see down here that we're seeing for each release
0:44
I want to navigate that relationship to the package
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and then get it's ID.
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And go to the package and get a summary.
0:50
So what we want to do is we actually want to just
0:53
have some way to get the package.
0:56
Now there's a ton of ways we could implement this.
0:59
Let me try to do it in a relatively efficient and fast way.
1:03
How do we exchange data with this template?
1:06
Well of course we use our view model, so let's go over here.
1:10
So we have the releases
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and we could just come up with self.packages
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and how do we get those?
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Well we go to our package service
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and we could say well give us all of the packages
1:20
that would be super inefficient.
1:22
We could say for all the releases here
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give us all those packages.
1:28
They come back as a list, that will work
1:30
but then how will we figure out which is the right one?
1:33
What we're going to do is we're going to come up with
1:34
something we're going to call a package look up.
1:37
And this is going to be a dictionary that given a package_id
1:40
will give us the package
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and the goal would be to go with these releases
1:45
and find all the packages they correspond to it.
1:48
So let's go over here and say packages
1:50
and when we get a list from our package_service
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this is the one we have to write right now.
1:54
We would get_package_by_id
1:56
and we want to get_packages_by_ids.
1:59
What ID's are we going to put in there?
2:01
Well let's go like this, package_ids.
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It's going to be a list comprehension.
2:06
So we're going to say are not package_id
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for r in self.releases, that's cool.
2:12
And then we're just going to pass this along.
2:13
This will be a simple in query
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as you'll see in just a second.
2:16
So let's go and have to write that.
2:19
This is going to be a list of str
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and what we get back, say, list of package.
2:26
Now down here, this turns out to be a super simple thing.
2:30
I'm going to go ahead and use a list
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to make sure that we convert that all the way to a list
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not some kind of partial executed query.
2:35
And we go down here and say, let's see, we want packages.
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So we're going to Package.objects(id__in=package_ids)
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That's it, we just want to get all the packages
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that happen to be in this set.
2:52
So we're going to pass in like say
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and you know who knows, some other thing past that.
2:58
We want to get all the packages who's ID is one of those.
3:02
And that's it, make sure we close everything off quickly.
3:05
Yeah it looks good.
3:06
So if we write this function, now we can come over here
3:09
and say okay we have these packages
3:10
but that's again not a clean way to look up things.
3:13
That's a flat list, so it'll be slow and cumbersome.
3:15
So we're going to create a dictionary
3:17
a little dictionary comprehension.
3:19
We're going to say p.id:p
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so given an ID we want the package for p in packages.
3:27
That's it, that's all the code we have to write.
3:28
It turns out it's a super fast query.
3:30
Now, how do we use this?
3:32
Well we have our little lookup here.
3:34
We're here, we've not talked about this
3:36
but you can actually create variables in Ginga.
3:39
So we can say set
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package=package lookup.get R not package ID.
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Something like this.
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So we know that the package is going to be there
3:50
because we generated it right.
3:52
We've gone to the releases
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and said give me all the packages where the ID's are this.
3:56
So now we can just go over here and say
3:58
put package, package, package, like so.
4:00
Let's see if that fixes it.
4:03
Make sure we run it, here try again.
4:06
Tada! And did it work? Yes of course it did.
4:09
There they are, so the home page is now fixed.
4:12
Now the question is, is that super slow
4:14
like is this going to be a big problem
4:16
going to the database twice instead of once?
4:18
No, we're actually going a couple of times
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going to the account
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going to make a couple calls here for these
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we're going to do, you know
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to load the rest of the page we're doing 2 queries.
4:29
Email literally says, and then for those releases
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give me all the packages.
4:32
Yeah it's a little bit, but let's see what the cost is.
4:37
If we go over here to our network
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and we load the page a few times
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now there's 6 or 7 milliseconds, that's pretty awesome.
4:44
So, I'm totally happy with the speed of this page.
4:46
If you're page is 6 or 7 milliseconds
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you should be happy, that's going to be really fast.
