Column types and constraints in Flask - Mini Project: Build & Apply

Column types and constraints

📖 Scenario: You are building a simple Flask app to manage a library's book collection. You need to create a database model to store book details with correct column types and constraints.

🎯 Goal: Create a Flask SQLAlchemy model called Book with columns that have specific types and constraints to store book information correctly.

📋 What You'll Learn

Create a Book model class inheriting from db.Model

Add a primary key column id with integer type

Add a title column with string type and maximum length 100, not nullable

Add an author column with string type and maximum length 50, not nullable

Add a published_year column with integer type

Add a isbn column with string type and maximum length 13, unique constraint

💡 Why This Matters

🌍 Real World

Defining database models with correct column types and constraints is essential for building reliable web applications that store and manage data accurately.

💼 Career

Understanding how to use Flask SQLAlchemy models with proper column types and constraints is a fundamental skill for backend web developers working with Python and Flask.

1

Set up the Book model with id column

Create a Flask SQLAlchemy model class called Book inheriting from db.Model. Add an integer column called id as the primary key.

Flask

from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy()

# Create Book model with id column
# Your code here

Need a hint?

Define a class named Book that inherits from db.Model. Use db.Column with db.Integer and primary_key=True for the id column.

2

Add title and author columns with constraints

Add a title column with string type, maximum length 100, and not nullable. Add an author column with string type, maximum length 50, and not nullable.

Flask

from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy()

class Book(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    # Add title and author columns below
    # Your code here

Need a hint?

Use db.String with the length inside parentheses. Add nullable=False to make the columns required.

3

Add published_year column with integer type

Add a column called published_year with integer type to store the year the book was published.

Flask

from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy()

class Book(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(100), nullable=False)
    author = db.Column(db.String(50), nullable=False)
    # Add published_year column below
    # Your code here

Need a hint?

Use db.Column(db.Integer) to define the published_year column.

4

Add isbn column with unique constraint

Add a column called isbn with string type, maximum length 13, and a unique constraint to ensure no duplicate ISBNs.

Flask

from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy()

class Book(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(100), nullable=False)
    author = db.Column(db.String(50), nullable=False)
    published_year = db.Column(db.Integer)
    # Add isbn column below
    # Your code here

Need a hint?

Use db.String(13) and add unique=True to the isbn column.