Building Data-Driven Web Apps with Pyramid and SQLAlchemy Transcripts
Chapter: Modeling data with SQLAlchemy classes
Lecture: Modeling packages
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It's time to bring SQLAlchemy
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into our application and start modeling things
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in the database, and actually using a database.
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How cool would that be?
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The place to start, I think, is modeling
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the tables with classes in SQLAlchemy.
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That's not actually the order, the first thing that happens
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in order when you execute the program.
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We have to do things like create the connection
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connect to the database, make sure the tables
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are configured and match the stuff that we're modeling
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things like that.
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But conceptually, the primary thing we're doing is modeling
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the database with these classes, so let's start there.
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Now, I personally like to have a separate dedicated section
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for the various classes.
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So we're going to create a sub-package.
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So here we have our data and let's start by modeling
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package, we'll call it packages, something like that.
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So here's how it works in SQLAlchemy.
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We have a class, we give it a name.
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Typically its name should be singular
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but, you know, however you want.
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It represents a single entity in the database anyway.
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It's going to derive from something here
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which we have to define, do that in a moment.
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And then into it, we're going to put
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a bunch of columns so it's going to be like an int.
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And then we'll have, say this be a name
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this is going to be a string, and so on.
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The things that we put on the right here
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are special SQLAlchemy values and they serve two purposes.
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At design time, they tell SQLAlchemy how to actually
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create the tables.
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At run time, they're effectively this
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integers, strings, and so on.
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So lets start by importing SQLAlchemy.
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Sometimes you'll see this as sa to keep things short
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so maybe we'll do that.
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Now notice it says this is not defined
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so let's install this.
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Cause, it's actually not defined.
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While we're doing that, we can go over here
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and also put it in the setup.
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Alright, now let's try it again.
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Oh perfect, so that's great.
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So we want a column, and in this column
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we would like.
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Actually, we were going to hijack the name thing
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and just make that the primary key.
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Remember the name of the package
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has to be unique on PyPI anyways.
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So let's just make this an sa.string
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and let's say primary key is true.
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Okay, starts to feel database-y right?
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The next thing, this is just something I like in databases
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is always knowing when a record was created.
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It lets you look at things that were recently created
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or see them in order, things like that.
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So let's add a created date.
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A datetime.
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And we're going to expand on these columns
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and make them a little bit nicer.
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But let's just get the basic structure in place first.
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A summary, now let me try to tie these back.
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So if we go over to SQLAlchemy
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here's going to be the name or the ID.
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This is the summary, right there
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that little tiny short thing.
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So we'll come over here this is the sa.column.
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And then, this part down here
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that is a big fat long description.
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So we'll have a description as well.
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We're also going to come over here
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and we'll have this little home page.
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We're going to be able to click on that
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so we need to model the home page.
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Also a string, and a docs URL some of them
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have the ability to say here are the documentation.
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and a package URL.
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Also you'll see that these have authors and maintainers
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and then, here they have an author.
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So the author's Mike Bayer
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and Mike Bayers's one of the maintainers as well
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but so is this person, okay?
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So we need to model it having a dedicated author
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but then also maintainers.
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Now we could do this to a relationship
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or we could put it directly on there.
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Maybe we want to keep it even in case
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they delete their account.
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So I'm going to put the author information here
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and we'll use a join to get to the maintainers.
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Then finally, these all have a license.
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Now we're going to use, oh let's see if we find the license here.
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Here we go.
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It's MIT.
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We're going to use a similar trick as we did here
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we would like to show just this simple information
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just the name of the license and maybe a link to it as well.
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Which is just the same as the title basically.
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So what we'd like to do is we could
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set this up in a way where we have to do a join
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on a license table because
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we're going to have a set of licenses.
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But, if we make the ID also be the name and be unique
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why would you have two licenses with exactly the same name?
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We won't.
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So, because the name would be unique we could use this
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and then this could actually both be just the string
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but also the relationship.
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So that'll avoid one join and make our table
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a little bit faster. That'll be sweet.
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So one more thing down here
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we're going to have releases and we're going to have maintainers.
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But the releases and the maintainers requires relationships.
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So we're going to come back to that in just a little bit
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but right now, things are looking pretty good for our table.
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If I go and start working with SQLAlchemy
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and saying here's my package table
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well one it needs a base class for this to work.
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But on the other, it's going to create a table called
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Package as a singular.
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I personally don't like that
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I'd prefer to have plural names and maybe lowercase.
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So we can control how this maps, so the database by putting
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a __tablename__ here.
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And we'll say lowercase packages
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so on the table it's going to show up as lowercase packages.
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But when we have one of them
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it's going to show up as a Package
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like a class would normally in Python.
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The other thing is sometimes nice when we're debugging this
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you would like to see in PyCharm
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without actually expanding all the bits
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what package you got back, and so on.
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So we're going to add a __repr__.
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And we'll just return something really simple here
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we'll just return.
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Just the ID, so it'll be package request
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package SQLAlchemy
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and so on if we're looking at a debugger output
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or printing a list of these things.
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Something like that.
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So that'll be a little bit helpful along the way.
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Alright so here's the basic concept
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of what we want to build.
