Add GraphQL API for batch user queries to reduce N+1 problems

Feature Request: GraphQL API

Problem

Our REST API has N+1 query problems when clients need related data:

// ❌ Current: N+1 queries (1 + 10 users = 11 queries)


const recommendations = await fetch('/api/recommendations?limit=10');
for (const rec of recommendations) {
  const user = await fetch(`/api/users/${rec.userId}`);  // N queries
}

Solution

Implement GraphQL API with DataLoader pattern:

query GetRecommendationsWithUsers {
  recommendations(limit: 10) {
    id
    score
    user {
      id
      name
      avatar
    }
  }
}

Benefits:

• Single query instead of N+1
• DataLoader batching (10 user queries → 1 batch query)
• p99 latency: Expected 412ms → 180ms

Implementation Plan

1. Add graphql-python dependency
2. Create schema with User and Recommendation types
3. Implement DataLoader for user batching
4. Add GraphQL endpoint /graphql
5. Migrate iOS app to use GraphQL

Related

• Blocks: #21 (closed) (p99 latency optimization)
• Related: acme-corp/mobile-section/ios-devs/ios-app#12 (closed) (iOS performance)