Skip to content
onwardpg

SQLAlchemy and Alembic

Alembic can render the upgrade from base to the current head without connecting to a database. This works well when the full revision chain can build a clean database.

Terminal window
alembic upgrade head --sql

Create an exporter that removes Alembic’s runtime revision table from the desired application schema:

#!/usr/bin/env bash
set -euo pipefail


alembic upgrade head --sql
printf '%s\n' 'DROP TABLE IF EXISTS alembic_version;'

Route log output to stderr in alembic.ini or env.py; stdout must contain SQL only.

[targets.app]
schema_command = ["bash", "scripts/export-alembic-schema"]
dev_database_env = "ONWARDPG_DEV_DATABASE_URL"
scratch_database_env = "ONWARDPG_SCRATCH_DATABASE_URL"
dev_mode = "workspace"

If the project has multiple Alembic heads, use heads or merge the branches intentionally. If offline rendering cannot execute a custom migration, use the Django-style adapter instead: apply alembic upgrade head to a fresh disposable PostgreSQL database and pg_dump --schema-only --no-owner --no-privileges the result.

Data migrations and dialect-dependent Python must remain deterministic from empty. As with every framework adapter, the output describes the destination; onwardpg generates the compatibility route.