generate-migration

name	generate-migration
description	Generate Django database migrations for Sentry. Use when creating migrations, adding/removing columns or tables, adding indexes, or resolving migration conflicts.

Generate Django Database Migrations

Commands

Generate migrations automatically based on model changes:

sentry django makemigrations

For a specific app:

sentry django makemigrations <app_name>

Generate an empty migration (for data migrations or custom work):

sentry django makemigrations <app_name> --empty

After Generating

1. If you added a new model, ensure it's imported in the app's __init__.py
2. Review the generated migration for correctness
3. Run sentry django sqlmigrate <app_name> <migration_name> to verify the SQL
4. Apply the migration locally with sentry django migrate <app_name> — Sentry's migration framework runs its safety checks on apply, so this catches unsafe ops (missing is_post_deployment, unsafe column changes, etc.) before CI does.

When editing a generated migration (e.g. swapping DeleteModel for SafeDeleteModel), leave the auto-generated is_post_deployment comment block in place. It documents a non-obvious flag with concrete guidance for future migration authors — useful context, not fluff. Only remove a comment if it's stale or contradicts the code.

Guidelines

Adding Columns

• Use db_default=<value> instead of default=<value> for columns with defaults
• Nullable columns: use null=True
• Not null columns: must have db_default set

Adding Indexes

For large tables, set is_post_deployment = True on the migration as index creation may exceed the 5s timeout.

Deleting Columns

1. Make column nullable (null=True) if not already
2. Remove all code references
3. Replace RemoveField with SafeRemoveField(..., deletion_action=DeletionAction.MOVE_TO_PENDING)
4. Deploy, then create second migration with SafeRemoveField(..., deletion_action=DeletionAction.DELETE)

Removing a Model (and eventually its table)

Two-phase process — the historical_silo_assignments entry must be added in phase 1.

Phase 1 — Remove the model class (MOVE_TO_PENDING)

1. Remove all code references
2. Replace DeleteModel with SafeDeleteModel(..., deletion_action=DeletionAction.MOVE_TO_PENDING)
3. Add the table to historical_silo_assignments in src/sentry/db/router.py (or getsentry/db/router.py for getsentry models). Pick the silo the model used — usually SiloMode.CELL.
4. Deploy

Phase 2 — Drop the table (DELETE)

After phase 1 has deployed, create a second migration with SafeDeleteModel(..., deletion_action=DeletionAction.DELETE). Leave the historical entry in place — the table-drop migration relies on it to resolve the silo.

Renaming Columns/Tables

Don't rename in Postgres. Use db_column or Meta.db_table to keep the old name.

Resolving Merge Conflicts

If migrations_lockfile.txt conflicts:

bin/update-migration <migration_name>

This renames your migration, updates dependencies, and fixes the lockfile.