SQLAlchemy ORM – Models & Tables

 

What is ORM?

ORM (Object Relational Mapping) lets you map:

  • Database Tables → Python Classes
  • Rows → Objects

Step 1: Setup Base Class

from sqlalchemy.orm import declarative_base

Base = declarative_base()

Step 2: Define a Model

from sqlalchemy import Column, Integer, String

class User(Base):
    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    name = Column(String)
    email = Column(String)

What’s Happening Here?

Code    Meaning
    __tablename__            Table name
    ColumnTable column
    IntegerData type
    primary_key=TrueUnique ID

Step 3: Create Database & Tables

from sqlalchemy import create_engine

engine = create_engine('sqlite:///example.db')

Base.metadata.create_all(engine)

This automatically creates:

CREATE TABLE users (
    id INTEGER PRIMARY KEY,
    name VARCHAR,
    email VARCHAR
);

Step 4: Create Session
from sqlalchemy.orm import sessionmaker

Session = sessionmaker(bind=engine)
session = Session()

Full Working Example
from sqlalchemy import Column, Integer, String, create_engine
from sqlalchemy.orm import declarative_base, sessionmaker

Base = declarative_base()

class User(Base):
    __tablename__ = 'users'
    
    id = Column(Integer, primary_key=True)
    name = Column(String)
    email = Column(String)

engine = create_engine('sqlite:///example.db')
Base.metadata.create_all(engine)

Session = sessionmaker(bind=engine)
session = Session()
Real-World Tip
Use separate files:
models.py
database.py
main.py
Common Mistakes
  • Forgetting Base.metadata.create_all()

  • Not setting primary key

  • Wrong data types

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