Subqueries & EXISTS

How to express SQL subqueries, EXISTS, and NOT EXISTS correctly in ActiveRecord, and why naive translations often return incorrect results.

N+1 Isn’t a Rails Problem: It’s a Query-Shaping Problem

Copied SQL into Rails and still got N+1? Rewrote in ActiveRecord and still got N+1? The fix is a set-based mental model: where N+1 really comes from, how to verify it, and the AR patterns that eliminate it safely.

December 22, 2025 5 min read

Why ActiveRecord Exists: The SQL Mental Model That Breaks in Rails

If you know SQL, ActiveRecord can feel pointless—until it saves you from consistency bugs. Here’s the mental model: where SQL alone breaks app invariants, and how to use AR without losing performance.

December 21, 2025 5 min read