Ecto Query Analysis

Skill: ecto-query-analysis

INVOKE BEFORE writing/reviewing queries, migrations, or Repo calls.

Use when

• Lists are slow; possible N+1.
• Adding associations or migrations.
• Reviewing Repo usage inside LiveView or GenServer.

Checklist

• Preload associations explicitly; avoid query-time N+1.
• Add DB indexes for foreign keys and common filters.
• Prefer select with fields needed; avoid loading blobs.
• Use Repo.transaction/1 for multi-step mutations.
• In LiveView, keep Repo calls out of handle_event unless throttled.
• Validate changesets in context/resource layer, not controllers.

Quick patterns

• Batch preload: Repo.preload(records, [:assoc]).
• Windowing/pagination: limit/2, offset/2, or keyset paging libs.
• Concurrency: wrap in Task.async_stream/5 only for read-heavy workloads; never inside Repo transactions.

Warnings to emit

• Repo calls in render.
• Queries inside Enum.map leading to N+1.
• Missing unique/foreign key indexes after migrations.