Reading records is about querying the database.

Basic lookups

user = User.query.get(1)

user = User.query.get(1)

• Returns the user with primary key 11 or NoneNone

Filter by column

user = User.query.filter_by(username="ravi").first()

user = User.query.filter_by(username="ravi").first()

• first()first() returns one row or NoneNone

Get all rows

users = User.query.all()

users = User.query.all()

Ordering

users = User.query.order_by(User.username.asc()).all()

users = User.query.order_by(User.username.asc()).all()

Common pattern: 404 if not found

In routes, you often want “not found” to return a 404.

Flask-SQLAlchemy provides:

user = User.query.get_or_404(user_id)

user = User.query.get_or_404(user_id)

That’s very convenient for web apps.

Performance note

all()all() loads everything into memory.

For very large tables, use pagination (limit/offset) or streaming approaches.