Active Record Patterns

Iron Laws

1. Use decimal or integer cents for money.
2. Prevent N+1 queries with intentional preload strategy.
3. Put invariants inside transactions and use locks when races matter.
4. Prefer after_commit for external side effects.
5. Keep schema constraints aligned with application validations.

Default Moves

• use foreign keys and indexes deliberately
• choose includes, preload, or eager_load intentionally
• use find_each for large backfills and batch work
• use optimistic or pessimistic locking where correctness depends on it
• make migrations reversible and production-safe