Rails Best Practices Core

Use this as the default baseline for Rails work. Distilled from 37signals codebases (Campfire, Fizzy) and DHH's review patterns.

Core Defaults

• Prefer clear, explicit code over clever abstractions. Abstractions must earn their keep; if you can't point to 3+ variations that need it, inline it.
• Keep controllers thin and put domain behavior in models.
• Prefer Rails conventions and built-ins before adding gems.
• Model state and behavior with domain concepts, not ad-hoc flags.
• Scope tenant/user data through ownership boundaries.
• Favor database constraints for hard invariants; only validate in AR when you need user-facing error messages.
• Keep interfaces small; don't add public methods that aren't used anywhere.
• Prefer write-time computation over expensive read-time composition (counter caches, delegated types, precomputed roll-ups, dependent: :delete_all when no callbacks needed).
• Use params.expect(...) for strong params in modern Rails.
• Let it crash: bang methods (create!), handle exceptions at boundaries. Only use ! when a non-bang counterpart exists.
• Fix root causes, not symptoms (e.g. enqueue_after_transaction_commit over retry logic for races).
• Ship tests in the same PR as behavior changes.