capsulflask

Python Flask web application for capsul.org

postgres database schema management

capsulflask has a concept of a schema version. When the application starts, it will query the database for a table named schemaversion that has one row and one column (version). If the version it finds is not equal to the desiredSchemaVersion variable set in db.py, it will run migration scripts from the schema_migrations folder one by one until the schemaversion table shows the correct version.

For example, the script named 02_up_xyz.sql should contain code that migrates the database from schema version 1 to schema version 2. Likewise, the script 02_down_xyz.sql should contain code that migrates from schema version 2 back to schema version 1.

IMPORTANT: if you need to make changes to the schema, make a NEW schema version. DO NOT EDIT the existing schema versions.

In general, for safety, schema version upgrades should not delete data. Schema version downgrades will simply throw an error and exit for now.

how to run locally

Ensure you have the pre-requisites for the psycopg2 Postgres database adapter package

sudo apt-get install python3-dev libpq-dev
pg_config --version

Create python virtual environment and install packages

python3 -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt

Run an instance of Postgres (I used docker for this, point is its listening on localhost:5432)

docker run -it -e POSTGRES_PASSWORD=dev -p 5432:5432 postgres

Run the app

FLASK_APP=capsulflask flask run