Building data-driven web apps with Flask and SQLAlchemy Transcripts
Chapter: Modeling data with SQLAlchemy classes
Lecture: Architecture
Login or
purchase this course
to watch this video and the rest of the course contents.
0:00
Before we actually start writing code
0:02
for SQLAlchemy, let's get a quick 50,000 foot view
0:05
by looking at the overall architecture.
0:09
So when we think of SQLAlchemy
0:11
there's really three layers.
0:13
First of all, it's build upon Python's DB-API.
0:17
So this is a standard API, actually it's DB-API 2.0
0:22
these days, but we don't have that version here.
0:25
This is defined by PEP 249
0:27
and it defines a way that Python can talk
0:31
to different types of databases using the same API.
0:34
So SQLAlchemy doesn't try to reinvent that
0:37
they just build upon this.
0:39
But there's two layers of SQLAlchemy.
0:41
There's a SQLAlchemy core, which defines schemas and types.
0:45
A SQL expression language, that is a kind of
0:48
generic query language that can be transformed
0:52
into a dialect that the different databases speak.
0:56
There's an engine, which manages things like the connection
0:59
and connection pooling, and actually which dialect to use.
1:02
You may not be aware, but the SQL query language
1:05
that used to talk to Microsoft SQL server
1:07
is not the same that used to talk to Oracle
1:09
it's not the same that used to talk to Postgre.
1:11
They all have slight little variations
1:13
that make them different, and that can make it hard
1:15
to change between database engines.
1:18
But, SQLAlchemy does that adaptation for us
1:21
using its core layer.
1:23
So if you want to do SQL-like programming
1:26
and work mainly in set operations
1:28
well here you go, you can just use the core
1:30
and that's a little bit faster
1:31
and a little bit closer to the metal.
1:33
You'll find most people, though
1:34
when they're working with SQLAlchemy
1:36
it will be using what's called
1:37
an Object Relational Mapper, object being classes
1:40
relational, database, and going between them.
1:43
So what you do is you define classes
1:45
and you define fields and properties on them
1:49
and those are mapped, transformed into the database
1:53
using SQLAlchemy and its mapper here.
1:56
So what we're going to do is we're going to
1:57
define a bunch of classes that model our database
2:00
things like packages, releases
2:02
users, maintainers and so on in SQLAlchemy
2:05
and then SQLAlchemy will actually create the database
2:08
the database schema, everything
2:10
and we're just going to talk to SQLAlchemy.
2:12
It'll be a thing of beauty.
