Antipattern: Migration Smells

The smells

• Referencing app models (User.find_each ...) — the model schema today is not the schema at migration time
• Irreversible change blocks doing execute "UPDATE ..." or destructive transforms
• Schema + data in the same migration — long UPDATEs during a deploy lock tables
• Missing indexes on foreign keys — joins get slower as data grows
• No null: false / default on add_column for required fields, leading to a follow-up "fix" migration

Why it hurts

• Fresh-environment setup (CI, new dev machine) becomes fragile as the model evolves
• Production deploys lock tables for minutes
• Rollbacks are impossible
• Joins on un-indexed FKs slow down at scale