🗃 Databases & SQL
How data survives between requests — tables, rows, sessions, migrations.
5 concepts
1
SQLAlchemy ORM
Map Python classes to DB tables. No raw SQL — just .query(Model).all().
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2
DB sessions
A session is a unit of work — track changes, commit, rollback. One per request.
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3
Relationships & joins
ForeignKey + relationship() lets you walk from a User to their Models with no SQL.
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4
Schema & migrations
init_db() runs CREATE TABLE IF NOT EXISTS on startup. For schema changes, use Alembic.
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5
Indexes
Speed up WHERE clauses at the cost of slower writes. Add to columns you filter on.
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