Building data-driven web apps with Pyramid and SQLAlchemy Transcripts
Chapter: Using SQLAchemy
Lecture: Querying data: Latest releases
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Now it's time to write another query.
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Actually we're going to write a couple queries
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to do something interesting and this actually might be
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the most complicated thing we do in the entire website.
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But, yeah you'll get to see a lot of stuff in action.
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So let's look over here real quick, here's our homepage.
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We're now driving that little slice out of the database.
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But remember this, this is just our fake data.
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So we want to actually go get the latest releases
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and then correlate those back
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to the latest packages and then show them here.
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Okay, how do we do that?
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Well, we're going to write a function.
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We want to say how many releases we want.
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So, we'll have a limit by default that limit is going to be 10.
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And it's going to return a list of package.
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List comes out of the typing model
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and the package that we already have.
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As always, everything starts like this
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and then we're going to return
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something down here at the end.
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So what happens at the middle?
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Well, the data model that I have chosen
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which was the most sort of naive and straightforward one
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maybe isn't the best for this site.
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Maybe it would have been better
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to have a little information on the package itself
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about when it was last modified but, it doesn't matter.
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What we're going to do is we're going to go
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get the latest releases
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find out the package IDs those correlate to
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and then we're going to go
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and get those packages out of the database.
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Great, so how do we do that?
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First we say releases is going to be
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and we're going to do a query.
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And the way that queries work is you to to your session
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and you say I'd like to create a query
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based on a particular thing.
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Here we're querying Release.
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Now we can do where clauses like this, filter.
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We can do orderby.
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So we actually don't want to do a filter.
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We just want to say show us the newest ones.
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And whenever you put some sort of qualifier here
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like a filter or a something that you're sorting by
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you use the type name.
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Release. and then what are you going to order by?
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Created date descending.
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Now PyCharm gives a warning
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that says descending doesn't exist.
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Nevermind it definitely does.
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That is going to give us back the releases.
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And we probably want to limit those by something.
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We don't want to get every release
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that's going to be a lot.
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So we'll say limit, we don't know for sure
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if maybe there's some kind
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of release done really quickly on the same package.
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So if we want to be sure that we give them
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say 10 or however many they're asking for
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we should probably double this or something.
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So I'll say the limit times two.
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And that's because we could have a really quick release
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of requests and then another one of requests.
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And then, you know we'd have two more
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than just the 10 releases.
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Actually get the 10 distinct packages.
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So we've got that.
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Now, what I want to do is come up with
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just the package IDs as a list of strings.
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I'm going to do that with a simple list comprehension.
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So say r.package_id for r in releases.
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In fact, if we wanted to do it I could even do it
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as a set comprehension. and that would give us
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distinct packages so we don't have to check
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for them existing twice. Beautiful.
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So, we've got the latest releases
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and now we've converted those to the distinct
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set of the latest package IDs.
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Now all you got to do is actually get the packages.
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I just realized my little trick here is going to be great but
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we're going to need packages in order as well.
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So let's do this.
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So now we need to do a query
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so we go back to the session.
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Go to query and this time on package.
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And how do we say I would like all the packages
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that are in this set of package IDs.
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Turns out that's super easy.
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Say filter
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package.id.in_
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Because in_ is a keyword they say in underscore you give it
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package IDs. That's it.
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That's going to give us all the matching packages.
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Now, we need to preserve the order.
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So, if all we wanted was the packages
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we could just kick those back.
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But remember, we asked for more than one
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so we don't get duplication, things like that.
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So, let's go and actually turn this into a quick dictionary.
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p. based on the ID.
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Do a little dictionary comprehension on that result
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and then finally we'll get these back.
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so we're just going to put stuff into this
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little results array right here and we're going to do it in order.
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There's probably a cool join way if I was better
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at data bases I could do that here
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but we're doing it this sort of convoluted way
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and it's going to work fine.
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Maybe not the most efficient, but not too bad.
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Alright, so we've got our results
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going through the releases in order
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and adding the packages in order
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and then we're adding them back.
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So this should work, but we're not calling it yet.
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Lets go over here, remember our get_test_packages?
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So we'll say, package service, not latest releases.
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Now, this is also not going to work
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because if we go over to our template
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it was using that fake data which had names.
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We don't have names, we have IDs.
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We actually do now have a description
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so let's put that in there. p.summary in here.
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Alright, let's give it a shot, see how we're doing.
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Here's where the stuff goes, we run it, Boom!
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Sweet, look at that. We've got 1, 2, 3, 4, 5
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6, 7, 8, 9, 10. Exactly like we asked for.
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Awesome! So now we've got our packages right here.
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It looks like awscli was the most recent release
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out of the ones that we have.
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And now if we click on it, well it doesn't take us anywhere.
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Let's do one more thing.
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We have this ID here, and lets fix r href.
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This is project/{id}, refresh
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Boom.
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That page needs some help.
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But this page, this page is done.
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This is awesome.
