activerecord

When a child record changes, you often want the parent cache key to change too. touch: true is a clean primitive for that. It keeps fragment caching sane without complex dependency graphs.

Normalize before validation to avoid “same email, different casing/whitespace” bugs. Keep normalization deterministic and small; put it in the model so imports, consoles, and controllers all behave the same.

When rendering JSON, the serializer layer can silently trigger extra queries. Force “preload then serialize” so your JSON rendering path is deterministic. This pattern scales well in Rails APIs.

Sometimes raw SQL is the cleanest approach—just keep it safe. Use exec_query with bind params instead of interpolating values. You get both safety and correctness with types.

Tagging systems can be expensive. For quick “top tags” features, compute from the join table with group and count. Avoid loading full taggable records.

Authorization filters often become string-SQL soup. Use Arel to build composable scopes that are still readable and safe. This snippet shows a “visible_to(member)” scope with a join and a condition that can evolve without turning into interpolated SQL

Inventory systems are concurrency systems. Lock the row, verify available quantity, then write the reservation in the same transaction. It’s the simplest correct starting point.

Avoid writing rows when nothing changed—especially in batch jobs. Check changed? or compute the would-be update and skip if identical. This reduces bloat and autovacuum pressure.

If multiple admins edit the same record, use lock_version. Rails will raise on conflicting updates, and you can show a friendly “this changed underneath you” message. It prevents subtle lost updates.

Race conditions happen. The correct “find or create” in production uses a unique constraint and a retry on conflict, not a naive check-then-insert. Let the database serialize the race.

Avoid loading whole records when you only need to know if something exists. exists? is good; for complex joins, a scoped select(1).limit(1) can be clearer and keeps the DB workload low.

I stopped doing row-by-row imports once they started hammering the DB. In Migration (unique index), I added a real uniqueness guarantee on provider + uid, because bulk writes only stay correct if the database can enforce constraints. Then, in Bulk ups