Creating Database Models

A model is a Python class that represents a database table.

Example: User model

python

from flask_sqlalchemy import SQLAlchemy
 
db = SQLAlchemy()
 
 
class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)
 
    def __repr__(self):
        return f"<User {self.username}>"

Key concepts

• User maps to a table (by default: user)
• each attribute maps to a column
• each instance maps to a row

Naming tables explicitly

python

class User(db.Model):
    __tablename__ = "users"
    # columns...

This avoids surprises, especially in bigger projects.

Nullable vs required

• nullable=False means the DB will reject NULLs

In practice:

• validate in forms (nice UX)
• enforce at database level too (data integrity)

Visualize it

Here’s the relationship between the two models: one User can own many Post rows.

diagram User and Post models mermaid

  classDiagram
  class User {
    id
    username
    email
  }
  class Post {
    id
    title
    body
    user_id
  }
  User "1" --> "*" Post

One-to-many relationship between User and Post

🧪 Try It Yourself

Exercise 1 – Create a Flask App

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Exercise 2 – Dynamic Route

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Exercise 3 – Return JSON

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