Antipattern: N+1 Queries (especially in views)

The smell

• Iterating a collection that calls .author, .comments.count, or other associations per row
• 50+ "SELECT ... WHERE id = ?" queries in dev log for one page render
• Bullet gem warnings
• .count inside a loop (where counter_cache or aggregation would do)

Why it hurts

• Latency scales linearly with rows
• DB connection pressure
• Slow in dev, catastrophic in prod
• Often invisible until production data shape changes

The fix

• Eager-load in the controller or scope: Post.includes(:author).recent
• Define a preloaded scope that bundles the standard eager-loads for that model — call it everywhere the view is rendered (Gierd convention from rails-models)
• For counts, use counter_cache or LEFT JOIN ... GROUP BY aggregation rather than .count in a loop
• Verify with Bullet in dev or assert_queries(N) in tests