Implement GraphQL

Use this skill when designing, implementing, or reviewing GraphQL APIs in a Rails application with the graphql-ruby gem.

Quick Reference

HARD-GATE

Tests gate implementation — write specs before resolver code (see write-tests).
Before shipping a resolver/mutation slice, ALL of the following must be true:
- N+1 Prevention: use `dataloader.with(Source, Model).load(id)` — NEVER `object.association`
- Authorization: sensitive fields have field-level guards (not type-level alone).
- Type Conventions: paginated collections use Types::*Type.connection_type, not plain arrays.
- Schema safeguards: AppSchema disables introspection in production and sets max_depth / max_complexity.
- TESTING.md: specs in `spec/graphql/` use `AppSchema.execute`. Never use HTTP controller dispatch for GraphQL specs.
- Error Handling: mutations return `{ result, errors }` with rescue blocks — no unhandled exceptions.
- Documentation: `description:` on every field in every type.
- Resolver Structure: dedicated resolver classes, not inline field blocks.
- Dataloader Priming: collection resolvers prime records for association fields that will call dataloader.

Core Process

1. SPEC: Write failing spec (happy path + auth + validation error case) — see TESTING.md.
2. TYPE: Define arguments and return types. Use connection_type for pagination shapes. Do not leak internal model names.
3. IMPLEMENT: Create resolver/mutation class delegating to a service object. Use dedicated classes instead of inline field blocks.
4. N+1 CHECK: Ensure dataloader is used on every association load. For list resolvers, prime the dataloader with the records returned by the relation before fields resolve associated objects. Use bullet and db-query-matchers in specs.

   # ✅ batches loads across all records
   def buyer
     dataloader.with(Sources::RecordById, Buyer).load(object.buyer_id)
   end

5. AUTH CHECK: Apply field-level guards where data is sensitive using Pundit or custom context guards.

   field :internal_notes, String, null: true do
     guard -> (_obj, _args, ctx) { ctx[:current_user]&.admin? }
   end

6. FINAL CHECK: Verify every HARD-GATE item is met. Ensure your mutations return { result, errors } shapes on failure.

   rescue ActiveRecord::RecordInvalid => e
     { order: nil, errors: e.record.errors.full_messages }

7. RUN: Ensure the full test suite is green before PR.

DO NOT proceed to step 3 before step 1 is written and failing.

Extended Resources (Progressive Disclosure)

Load these files only when their specific content is needed:

• TESTING.md — For the spec template, paths, and checklist (happy path, unauthenticated, unauthorized, validation errors, N+1 counts, limits).
• EXAMPLES.md — For detailed code examples of dataloaders, mutations, and types.

Output Style

When implementing GraphQL, your output MUST include:

1. Schema contract — Types, fields, arguments, nullability, descriptions, and connection shape.
2. Resolver/mutation structure — Dedicated class names and service-object delegation points.
3. N+1 prevention — Dataloader source and every association load it protects.
4. Authorization and limits — Field-level guards, Pundit checks, introspection/depth/complexity decisions.
5. Error shape — Mutation { result, errors } or equivalent structured failure behavior.
6. Verification — spec/graphql/ commands covering happy path, auth, validation errors, N+1 counts, and schema limits.
7. Hard-gate checklist — Explicitly verify all hard-gate items, including resolver structure, type conventions, and dataloader priming.
8. Language — Must be in English unless explicitly requested otherwise.

Integration