This repository contains the source code examples for the second edition of my O'Reilly book Flask Web Development.

The commits and tags in this repository were carefully created to match the sequence in which concepts are presented in the book. Please read the section titled "How to Work with the Example Code" in the book's preface for instructions.

The code examples for the first edition of the book were moved to a different repository: https://github.com/miguelgrinberg/flasky-first-edition.

This fork now adopts a pip-tools based workflow.

Layered files:

1. *.in (e.g. requirements/base.in, dev.in, docker.in, heroku.in, prod.in) list direct dependencies (unpinned, may include -r base.in).
2. *.txt are generated lock files (exact versions + provenance comments) via pip-compile and are what you install from.

Common commands:

Generate / refresh all locks:

Option 1 (script):

./scripts/update_locks.sh            # all
./scripts/update_locks.sh dev        # only dev
U=1 ./scripts/update_locks.sh base   # upgrade base deps
UPKG=Flask,SQLAlchemy ./scripts/update_locks.sh base dev
HASHES=1 ./scripts/update_locks.sh   # include hashes

Option 2 (Makefile):

make lock-all
make lock TARGETS="base dev"
U=1 make lock TARGETS="base"

Install (dev):

pip install -r requirements/dev.txt

Install (production):

pip install -r requirements/prod.txt

Install (Heroku / docker images respectively):

pip install -r requirements/heroku.txt
pip install -r requirements/docker.txt

Exact env sync (will uninstall anything not in the files):

pip install pip-tools
pip-sync requirements/prod.txt      # or dev.txt etc.
# OR via Makefile
make sync FILE=requirements/dev.txt

Upgrade strategies (via script / Makefile):

• All packages (base): U=1 ./scripts/update_locks.sh base (or U=1 make lock TARGETS="base")
• Single package upgrade (example Flask): UPKG=Flask ./scripts/update_locks.sh base
• Multiple specific packages: UPKG=Flask,SQLAlchemy ./scripts/update_locks.sh base
• Add hashes for stronger supply‑chain guarantees: HASHES=1 ./scripts/update_locks.sh (combine flags, e.g. U=1 HASHES=1 ./scripts/update_locks.sh base)

Direct pip-compile commands remain possible if you prefer manual control; the script simply wraps them with sensible defaults.

Recommended workflow:

1. Edit a *.in (add/remove direct deps).
2. Re-run selective pip-compile (only affected stacks) or the full batch.
3. Run tests, lint, security scan.
4. Commit changed *.in + corresponding *.txt together.

Legacy constraints*.txt snapshots have been superseded by the generated *.txt lock files.

This Flask application supports both MySQL and PostgreSQL databases.

• Python Library: mysqlclient
• Connection String: mysql://username:password@host:port/database
• Docker Service: Available in docker-compose.yml

• Python Library: psycopg2-binary
• Connection String: postgresql://username:password@host:port/database
• Alternative Format: postgres://username:password@host:port/database

Set the DATABASE_URL in your .env file:

# MySQL example
DATABASE_URL=mysql://flasky:password@localhost:3306/flasky

# PostgreSQL example
DATABASE_URL=postgresql://flasky:password@localhost:5432/flasky

# Install MySQL server
sudo apt-get install mysql-server

# Create database and user
mysql -u root -p
CREATE DATABASE flasky;
CREATE USER 'flasky'@'localhost' IDENTIFIED BY 'password';
GRANT ALL PRIVILEGES ON flasky.* TO 'flasky'@'localhost';
FLUSH PRIVILEGES;

For production/remote access:

CREATE SCHEMA `flasky` DEFAULT CHARACTER SET utf8mb4;
CREATE USER 'flasky'@'%' IDENTIFIED BY 'flasky.2025';
GRANT ALL PRIVILEGES ON flasky . * TO 'flasky'@'%';

# Install PostgreSQL server
sudo apt-get install postgresql postgresql-contrib

# Create database and user
sudo -u postgres psql
CREATE DATABASE flasky;
CREATE USER flasky WITH PASSWORD 'password';
GRANT ALL PRIVILEGES ON DATABASE flasky TO flasky;

For production setup:

CREATE USER flasky WITH PASSWORD 'flasky.2025';
CREATE DATABASE flasky OWNER flasky;
GRANT ALL PRIVILEGES ON DATABASE flasky TO flasky;

Connect to PostgreSQL:

psql -h 127.0.0.1 -U flasky

Use the provided docker-compose.yml which includes MySQL service:

docker-compose up -d

For PostgreSQL with Docker, modify docker-compose.yml to use postgres image instead of mysql.

After setting up your database:

# Initialize migration repository (first time only)
flask db init

# Create migration
flask db migrate -m "Initial migration"

# Apply migration
flask db upgrade

The application includes database tests. Run them with:

python -m pytest tests/

• MySQL: Use mysqlclient for better performance in production
• PostgreSQL: Use psycopg2 (compiled) instead of psycopg2-binary for production
• Connection Pooling: Consider using connection pooling for high-traffic applications
• SSL: Enable SSL connections in production environments