N1 Check

What the source does

• FilesystemNone observedNo reads or writes in the source
• NetworkNone observedNo outbound calls in the source
• ShellNone observedNo commands run in the source
• DependenciesPinnedNothing floats
• SecretsNone foundNo keys in source

Five audit layers

Gates applied: no behavioural pass.

Audit 0.4.1 · source sha 492f17636999 · 18 Oct 2026Report an issue or request a re-scan

• Publisheroliver-kriska GitHub userOwner of the repository this skill is read from
• Source folderoliver-kriska/claude-elixir-phoenix/plugins/elixir-phoenix/skills/n1-checkThe exact folder we audited
• LicenceMITAs the repository states it
• Commit pinned for this verdict492f17636999A new audit runs when the source changes
• Repository statusNot archivedLast push 2 days ago
• Sandboxed runNot runSkills are read, not executed; layer L4 is skipped

Its description: Detect N+1 query anti-patterns specifically — Repo calls inside Enum/for loops, missing preloads on associations. Use when N+1 is explicitly suspected, NOT for unrelated Ecto questions or wider database performance.

---
name: n1-check
description: "Detect N+1 query anti-patterns specifically — Repo calls inside Enum/for loops, missing preloads on associations. Use when N+1 is explicitly suspected, NOT for unrelated Ecto questions or wider database performance."
effort: medium
---

# 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 (`for`, `Enum`) in `lib/**/*.ex`.

## Analysis Command

Use Grep to find all `Repo.` calls in a context module, then verify each query has appropriate preloads.

## References

For detailed patterns, see:

- `${CLAUDE_SKILL_DIR}/references/preload-patterns.md` - Efficient preloading strategies
- `${CLAUDE_SKILL_DIR}/references/query-optimization.md` - Query batching techniques

Excerpt, first 2,147 characters of SKILL.md, verbatim from the audited commit. It is text from someone else’s repository, quoted so you can judge it before your agent reads it.

git clone https://github.com/oliver-kriska/claude-elixir-phoenix
git -C claude-elixir-phoenix checkout 492f17636999

Works in

1. 2026-10-18
   ✓SAFE B 89 / 100

   first audit · source 492f17636999

Questions about N1 Check

• github.com/oliver-kriska/claude-elixir-phoenix/tree/main/plugins — the audited source at commit 492f17636999 and every finding aboveObserved · 18 Oct 2026

Spotted something wrong? Report a correction · Methodology