Building Data-Driven Web Apps with Pyramid and SQLAlchemy Transcripts
Chapter: MongoDB edition
Lecture: Rewriting our queries
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We saw our site doesn't work
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because we're trying to access SQLAlchemy
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which we're no longer configuring in our
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various data services, so now what we're going to do
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is go rewrite these data services
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like this last latest releases.
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It might sound challenging, but it turns out
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to be super easy, let's go do it.
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Here's part of that design pattern thing I spoke about.
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We've taken every single bit of data access
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and we've isolated it down into just these two modules
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a couple of functions within each.
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So that means, within the view models
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within the controller methods, all of that stuff
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none of them care about the details
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of how we talk to the database
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they just expect classes back.
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And as long as the classes have
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the right type, it'll be okay.
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So, that's the beauty right here.
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Let's go down, and all we have to do
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is rewrite these queries, rewrite how
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we get package count, for example.
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So let's get to it, it's going to be really quick.
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We're going to change this to nosql.
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We don't use this unit of work pattern for MongoEngine.
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I do kind of like the unit of work pattern
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but they don't use it, so here we go.
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Now instead of going and creating the query on a session
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we go to the class and we say objects.
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Now this is just a blank query
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there's not filters and stuff, but we could put those here.
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Okay, so that's going to do that one, let's do Release.
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This is going to do ...
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objects().count().
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Okay, not too hard so far.
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That's one's kind of the hardest one
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so let's put that away for a minute.
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So this one kind of looks complicated.
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Remember the joins and all that.
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So we're going to find a package by name
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so we go to the package, and go to it's objects
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now we can .. the filter does work
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exactly like this, but what we can do is
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if we're just doing one filter
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we can just put that ... right there.
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We don't need this filter statement.
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OK, so it's kind of equivalent.
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The other thing that's different
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is we don't use double equal, we use single equal
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and then we don't use the type, we just say the field.
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Okay, so it's just id is that.
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At this point, we can make this
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look a lot cleaner, like that.
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That's pretty slick.
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Alright, we got one more down here.
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We want to go to create a list of the results of this query.
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Objects and then we're going to get the limit
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by whatever that value is.
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Look at this, this is comin' along pretty easy, right?
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Now, finally, this one here.
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So we want the releases ...
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Objects ... Order by ...
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Also exists in MongoEngine, but this
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syntax doesn't exist.
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If you want to sort by this field
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descending, you just put it as
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a string with a minus in the string.
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I don't like that as much, but that's how it works.
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That's it, this one's done, and then down here, again
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we're going to go to our package
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it's going to be .objects()
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and this one gets pretty interesting.
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See how we're doing this query of
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I like the ID to be contained within this set?
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Same idea in MongoDB, but it's going to go like this.
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Say id instead of dot, you do id__in
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to apply the operator and you don't have the ... there
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and you just say equal the set.
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Different, not super hard.
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I think, I think this might do it.
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This may well do it.
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Let's run and see what happens.
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Now we didn't change the user thing
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so that might, that might pose a problem, let's find out.
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None type is callable.
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Where is this?
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Yep, user service, user count, okay.
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We got to do that over here.
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I think just the one, so, instead of data
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we'd have nosql, we don't have unit of work
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we have .objects(). Let's try again.
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I think that might be enough to make it run.
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Boom, look at that, it's working! Like a champ.
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If I login there's going to be some minor issues.
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We don't have our data yet, but it's great.
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We can even come over here and try to get to a project.
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ike request, it's not in the database
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so it should 404, right?
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Perfect, didn't crash, it went to the database
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said eh, not here, 404.
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Of course it's not here 'cause the database is empty.
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We're going to solve that problem in a minute
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but this, this is pretty awesome.
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We now have our stuff converted.
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Let's go ahead and finish out this user stuff here.
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Turns out there's just a few steps left.
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Okay, remember, create the user, all good.
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Instead of all of this, you just say user.save().
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So here we're going to do a query
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for the user by email, actually
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we have a little function below called
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find_user_by_email, let's just re-use that.
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I think, it's going to do this as well.
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Alright, that's pretty easy.
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It's not, but it will now.
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So again, we don't do it this way
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we go and say .objects()
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and we don't use the type name
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we do assignment like so. That's it.
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We have now entirely re-written our app.
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100 percent, to move from SQLAlchemy to MongoDB
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using MongoEngine, period, done, that's all of it.
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And, most importantly, notice we've only changed
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these two files that are focused on data access.
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Granted, we had to add these, because, well
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you can't have the entities without adding them
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but it's not like we re-wrote a
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whole bunch of stuff up here.
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Notice, no color changes in this implementation.
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Down in the view models, there's tons of them
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all over the place, no changes.
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Because we implemented this beautiful
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little pattern of hiding our data access
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here, and then exchanging classes.
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Now, there's little tiny issues going on.
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Like, let's see if we can find one, maybe this one.
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No, I was thinking maybe some of them import.
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pypi.data.user, and things like that
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for, like type-ins, but they're not even doing that.
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If they did, we'd just change it
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I've chosen these to be exactly
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at least really really close in terms of names
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of the columns and stuff, so that
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it really doesn't matter which one you say it is
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but it's better to have it correct, of course.
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Almost works. There's one ultra small problem
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well, first, the data's not there
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but there's one other small problem that we got to fix.
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It's going to require us to change the base ViewModel
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so, this thing I told you about, the beauty
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there's one tiny detail, and the detail
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is because, over here, the user is using the default id
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which is what's called an ObjectId
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whereas in this one, it's using an integer.
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The cookie handling needs to be
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slightly adjusted to deal with that.
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No problem there.
