GRAPHQL Schema Designer

Overview

Designs complete, production-ready GraphQL schemas including type definitions (scalar, object, input, enum, interface, union), queries, mutations, subscriptions, resolver patterns, solutions to the N+1 problem (DataLoader), pagination (cursor-based), error handling via union types or extensions, and guidance on schema-first vs code-first, stitching vs federation.

When to Use This Skill

• Building a new GraphQL API or refactoring an existing one.
• User describes data model or operations ("users can query their orders with line items and status history").
• Choosing between REST and GraphQL or improving an existing GraphQL schema.

Prerequisites

• GraphQL server (Apollo Server, Yoga, Pothos, Nexus, or codegen-based).
• Database or data sources the resolvers will call.
• For advanced: DataLoader, Redis for caching, understanding of federation.

Steps

1. Schema-first vs code-first decision:

   • Schema-first: SDL + resolvers (good for collaboration with frontend).
   • Code-first: TypeScript classes/decorators or builder (better DX, type safety).

2. Core type system:

   • Scalars (ID, String, Int, Float, Boolean, custom DateTime, JSON).
   • Enums for status fields.
   • Input types for mutations.
   • Interfaces and unions for polymorphism.

3. Query design:

   • Root queries should be specific (not generic "node" unless using Relay).
   • Always think about what the client actually needs (avoid over-fetching by design).

4. N+1 problem & DataLoader:

   • Identify batchable loads (e.g., user for each post).
   • Create DataLoader per type.
   • Use in resolvers: loader.load(id).

5. Pagination:

   • Prefer cursor-based (Relay connection spec or simple after + first).
   • Provide edges + pageInfo or a simpler items + hasMore.
   • Offset pagination only for admin/internal use cases.

6. Mutations & input validation:

   • One mutation per action.
   • Return the mutated entity or a payload type.
   • Use input objects.

7. Error handling:

   • Use union error types (e.g., CreatePostResult = Post | ValidationError | Unauthorized).
   • Or GraphQL errors with extensions.

8. Subscriptions (real-time):

   • Use graphql-ws or Apollo subscriptions.
   • Pub/sub backend (Redis, in-memory for dev).

9. Output:

   • Complete SDL or code-first schema.
   • Resolver map or class.
   • DataLoader setup example.
   • Pagination helper.
   • Example queries/mutations in the response.

Examples

Full schema for a blog + comments + users (with DataLoader, cursor pagination, and union error types) is provided, along with resolver skeleton and subscription example.

Edge Cases & Error Handling

• Circular references: Use lazy loading or interfaces.
• Authorization: Perform auth checks inside resolvers or with middleware/directives.
• Rate limiting & complexity: Use graphql-query-complexity or persisted queries.
• Schema evolution: Deprecate fields instead of removing; use versioning or federation for major changes.

Verification

1. Load the schema in GraphQL Playground / Apollo Studio / Insomnia.
2. Run example queries and mutations — they return expected shapes.
3. Enable DataLoader batching and confirm single DB query for lists.
4. Test pagination cursors with real data.
5. Subscriptions fire on mutation.
6. Success: Schema is expressive, performant (no N+1), type-safe on both sides, and easy to evolve.

References

• GraphQL.js
• Apollo Server
• Relay Cursor Connections Spec
• DataLoader
• Pothos GraphQL or Nexus
• GraphQL Error Best Practices