N+1 problem, DataLoader, persisted queries, federation.

GraphQL — Queries, Mutations, Subscriptions, and Schema Design

GraphQL is a query language and runtime where clients specify exactly the data they need. Single endpoint, strongly typed schema, no over/under-fetching. Queries (read), Mutations (write), Subscriptions (real-time). The N+1 problem: resolving a list of N users then N separate DB queries for each user's posts. DataLoader solves this by batching and caching. Schema federation (Apollo Federation, GraphQL Mesh) composes schemas from multiple services.

Interactive Pipeline Flow

UnderstandImplementOptimise

📐 Schema — SDL type definitions

Schema (SDL): type User { id: ID!, name: String!, posts: [Post!]! }. type Post { id: ID!, title: String!, author: User! }. type Query { user(id: ID!): User }. This is the contract.

Architecture Diagrams

Federated schema composition from multiple subgraphs.

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Key Design Decisions

📦DataLoader is mandatory for any list resolver

Every resolver returning a list of items where sub-fields require additional queries MUST use DataLoader. Without it, a query for 100 users with their posts fires 101 DB queries. With DataLoader: 2.

📐GraphQL schema is your team contract

The SDL schema is the source of truth for what the API can do. Use Schema-first development: design the schema, generate types, then implement resolvers. Type-safe everywhere.

💾Persisted queries for security and performance

Persisted queries prevent arbitrary query execution (security) and reduce request size from thousands of characters to a short hash. Required for production mobile apps.

Discussion