Full Web Apps with FastAPI Transcripts
Chapter: async databases with SQLAlchemy
Lecture: The remaining database queries
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Over here in the package service, those were the final queries that we needed to convert to async.
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And because it's exactly the same as what we've been doing, I decided to go ahead and do the conversion, and we'll just talk through it real quick.
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So for the release_count, just like we saw before, we're gonna do a select with a function count of Release.id and execute it, that's
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pretty straightforward, at least given what we saw for users. package_count, exactly the same. But Package instead of Release. This latest_packages,
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remember, this was our most complicated query that we had in our system. But from here to here, it was exactly the same as the old query.
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We just have to, instead of doing session.query, we just say "select" and then you can't do the all() anymore, what you do is just scalars() like that.
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Then we did this little set trick just like before to make sure we get only unique ones in case a package has had a release within a couple of times of
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some of the other ones, right? We had a little duplication, and that gets rid of it. get_package_by_id again super similar.
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You get a select, here your filter just like before, await executing it. And this first() is now scalar_one_or_none.
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Also converting the latest release for a package. Very, very straightforward. This was basically the same thing.
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Execute it, these are scalar_one_or_none, good to go. So that's it. Those are all the queries. But what I wanted to do together with you,
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it's just integrate these queries back into the rest of the application. So let's go find where this is being used and update it.
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It should be just that IndexViewModel right there and notice PyCharm is saying all
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of these, all of these are a problem. None of them are returning integers or lists, what in fact they're returning is coroutines.
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We gotta execute the coroutine and get its value out by awaiting it. And then this one, we now can say more concretely,
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this is a list of Package. That will give us a tiny bit more autocomplete. So release count, package count,
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we already just took care of. latest_packages, I believe this is also just used in that one location.
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Yes, it is and we're doing things, I'll get there. get_package_by_id, where is that being used?
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You'll find it, there you go. It's over in this DetailsViewModel. Now, this is one of those that's going to take some work. We now have to await this,
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and this one is also async, so we're gonna have to await that. That means we will need to do some sort of work.
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Let's reorder this a little bit, like this. We need to do some sort of work in order to allow us to await this. Like I said, constructors,
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the dunder init, cannot be asynchronous. That was already down there, so I guess that was just duplicate.
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So this part right here needs to run somewhere else. However, these things need to be defined as optional things of whatever they are, so
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this means Optional[Package], so we can write this code here, define it correctly, and then load it up. Come over here,
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same type of thing but for Release. Package release, the latest version, that's already set up there.
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Okay, good. So now all we gotta do is make an asynchronous function that we can call wherever we were using this before.
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Remember, it's called DetailsViewModel, and it's in packages. So that would mean it's in the package view detail function.
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There's only one, apparently, so that kind of solves that right? But the last thing to do is make this async and await vm.load() we
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should be good to go with that. We may have just done it. That might have been the last function. Let's see, where is this one being used?
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Yeah, it's already being awaited. That's cool. Oh, however, I just now noticed, you may have have already noticed that, we need a "self" over here to
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pass it along, perfect. All right, let's go click around the site and see if it works. Make sure there's no "you forgot to await something"
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warning. So here we have number of projects, releases, users. Those all look real. Notice
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I added two more by adding those Sarah Jones3 and 4 in, which is pretty cool. We have the awscli.
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The part that we just worked on is, what happens if I click this? Mmm, not something good. What has happened here?
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Multiple rows were returned, right here. Oh, yeah, we just want to say scalar I believe. It's, scalar_one_or_none is if I'm trying to get some kind
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of like user or something were it's supposed to be unique. Let's see about that. There we go. Because, of course, there's multiple releases.
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We just want one, which is the latest. Alright, perfect. This is working right here.
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Looks like everything's good. We could check out the home page, that awscli sure looks like it, so that, that's working.
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Let's click on one other, gevent, perfect. There's details about the gevent, the library, and this is all working.
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So homepage, package is good. Let's just one more time. Log in, log out. We log in, log out and finally do one more register.
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I'm sure this will work because I've done it so many times, but we'll do a test with the wrong one there, already exists. That's right,
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we wanted Sarah Jones5, and Sarah Jones5 is now registered. That's it. Let's double check, really quick here,
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make sure there's no "you forgot to await something". No, no warnings either. Looks like we got everything converted over to this new
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SQLAlchemy style of programming. Now I want you to just think back to that diagram
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where we saw the animations where we saw all the interactions, so over here. Here, where we saw those interactions when our request would come in to,
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like, slash project slash whatever. What are we doing here? We're going. And we're saying I want to start a little bit of work.
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So this whole section here is gonna run synchronously, which builds up the variables to work with.
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And then we're gonna await this load jumping back over here. This is where we're going to the database to do a query and say: you know,
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anything that's happening right now, if another request comes in while we're waiting for the database, cool, just go let that request do its thing,
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maybe start off another database call, when this database gets back to us, just put the answer right there.
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Oh, now we're gonna start another database call, and if anything happens during that, it's cool, just go process it. When this one's finished,
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drop the answer right there. And then a little tiny bit of work, like checking for None on two items and a string format.
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Most everything happening in this whole series right here is about waiting on the database, in
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those two database calls. Were doing that asynchronously, that means we're not blocking up the
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server, were not consuming hardly any resources while that's happening, on the web server.
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Obviously the database is working its heart out, trying to give us the answers, right? using its indexes and doing its thing.
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But as long as the database can handle the traffic, this particular part of our application is not gonna be the bottleneck,
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and that is super, super cool. It's possible because async and await, we were able to use async and await because we're using the latest SQLAlchemy,
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the beta version that supports actually asynchronously talking to the database. Super cool, hopefully you'll appreciate this a ton.
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I think it's really, really neat, and it unlocks some amazing potential for your web app.