Migration Gotchas

GeneralManager integrates tightly with Django migrations. Keep the following tips in mind to avoid unexpected issues.

Import order

Always import manager modules in apps.py (inside AppConfig.ready()). If Django does not evaluate your interfaces, it cannot generate migrations for the derived models.

Model renames

When you rename a manager attribute or interface field, update existing migrations accordingly. Django may consider it a field deletion plus addition otherwise.

Measurement fields

MeasurementField stores value and unit columns. When you change the base unit, create a data migration that rescales stored values to the new unit to avoid inconsistent data.

Read-only interfaces

Read-only data synchronises _data entries during startup. If you remove entries, they are soft-deleted (Meta.use_soft_delete = True is forced for read-only managers). Write data migrations when you need permanent removal.

Historical data

Database interfaces integrate with django-simple-history. When you backfill migrations, ensure history tables are populated before managers expect them.

Rolling back

Because managers call full_clean() during operations, old migrations can fail if data violates new validation rules. Plan rollback steps by capturing export snapshots before applying schema changes.