ecton1-check

# N+1 Query Detection Identify and fix N+1 query anti-patterns in Ecto/Phoenix applications. ## Iron Laws - Never Violate These 1. **Never access associations without preload** - Always preload before `Enum.map` 2. **No Repo calls inside loops** - Restructure to batch queries 3. **Preload at context boundary** - Load associations in context, not controllers/views 4. **Use joins for filtering** - Use `join` + `preload` when filtering by association ## Detection Patterns ### Pattern 1: Enum.map with Repo ```elixir # BAD: N+1 queries users |> Enum.map(fn user -> Repo.get(Order, user.order_id) end) # GOOD: Single query with preload users |> Repo.preload(:orders) ``` ### Pattern 2: Association Access Without Preload ```elixir # BAD: Lazy loading triggers N queries for user <- users do user.posts # Triggers query for each user! end # GOOD: Eager load first users = Repo.all(User) |> Repo.preload(:posts) for user <- users do user.posts # Already loaded end ``` ### Pattern 3: Nested Association Access ```elixir # BAD: N+1 for nested associations user.posts |> Enum.map(fn post -> post.comments end) # GOOD: Nested preload Repo.preload(user, posts: :comments) ``` ## Quick Detection Commands Use Grep with context lines (`-B 5 -A 5`) to find `Enum.map` near `Repo.` calls in `lib/**/*.ex`. Use Grep to find association access patterns (`.posts`, `.comments`, `.orders`) in `lib/**/*.ex`. Use Grep with context (`-B 3`) to find `Repo.get` or `Repo.one` near loop patterns (`...