Alembic Installation and Setup

🔍 Why Alembic?

Currently, if we want to make changes to our database tables (for example, adding a column), we would have to:

• Delete the existing table in SQLite, MySQL, or PostgreSQL.

• Rerun the application so SQLAlchemy can recreate the table.

• Unfortunately, this deletes all existing data.

Alembic solves this problem by allowing us to modify tables without losing data. It manages migrations efficiently, even in production.

💻 Installing Alembic

First, we need to install Alembic in our project.

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Make sure Virtual Environment is active and You are in TodoApp

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Terminal Command:

pip install alembic

This will download and install Alembic along with all required dependencies.

⚡ Initializing Alembic

Once Alembic is installed, we need to initialize it for our project:

alembic init alembic

After running this command, Alembic will create:

• Alembic version information

• Alembic scripts and environment

• alembic/ directory

• alembic.ini configuration file

• README file

📁 Understanding the Alembic Project Structure

1. alembic.ini

This configuration file contains information about:

• Database connection URL (sqlalchemy.url)

• Migration script locations

• Time zone and other Alembic options

In future sessions, we will update the SQLAlchemy URL to point to our project database.

2. alembic/ Directory

The alembic/ directory contains all the environmental scripts and migration files. Key components include:

• Versions folder – stores upgrade and downgrade migration scripts

• env.py – contains environment setup for Alembic; we’ll modify this for our project database

• README – generic information about Alembic environment

• script.py.mako – template for migration scripts (optional; mostly for reference)

This directory is where all migration history is maintained, ensuring your database can evolve without losing data.