Building Data-Driven Web Apps with Flask and SQLAlchemy Transcripts
Chapter: Modeling data with SQLAlchemy classes
Lecture: Architecture
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Before we actually start writing code for SQLAlchemy, let's get a quick 50,000 foot view by looking at the overall architecture.
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So when we think of SQLAlchemy there's really three layers. First of all, it's build upon Python's DB-API.
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So this is a standard API, actually it's DB-API 2.0 these days, but we don't have that version here. This is defined by PEP 249
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and it defines a way that Python can talk to different types of databases using the same API. So SQLAlchemy doesn't try to reinvent that
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they just build upon this. But there's two layers of SQLAlchemy. There's a SQLAlchemy core, which defines schemas and types.
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A SQL expression language, that is a kind of generic query language that can be transformed into a dialect that the different databases speak.
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There's an engine, which manages things like the connection and connection pooling, and actually which dialect to use.
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You may not be aware, but the SQL query language that used to talk to Microsoft SQL server is not the same that used to talk to Oracle
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it's not the same that used to talk to Postgre. They all have slight little variations that make them different, and that can make it hard
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to change between database engines. But, SQLAlchemy does that adaptation for us using its core layer. So if you want to do SQL-like programming
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and work mainly in set operations well here you go, you can just use the core and that's a little bit faster and a little bit closer to the metal.
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You'll find most people, though when they're working with SQLAlchemy it will be using what's called an Object Relational Mapper, object being classes
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relational, database, and going between them. So what you do is you define classes and you define fields and properties on them
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and those are mapped, transformed into the database using SQLAlchemy and its mapper here. So what we're going to do is we're going to
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define a bunch of classes that model our database things like packages, releases users, maintainers and so on in SQLAlchemy
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and then SQLAlchemy will actually create the database the database schema, everything and we're just going to talk to SQLAlchemy.
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It'll be a thing of beauty.