Overview
GraphQL is a query language for APIs that allows clients to request exactly the data they need, making APIs more efficient and flexible.
Core Concepts
Schema
- Defines available data and operations
- Strongly typed with SDL (Schema Definition Language)
- Self-documenting API
Queries
- Read operations to fetch data
- Declarative data fetching
- Nested and related data in single request
Mutations
- Write operations to modify data
- Similar to queries but for changes
- Return modified data
Subscriptions
- Real-time data updates
- WebSocket-based communication
- Push-based data flow
Schema Definition
Types
type User {
id: ID!
name: String!
email: String!
posts: [Post!]!
}
type Post {
id: ID!
title: String!
content: String!
author: User!
publishedAt: DateTime!
}Queries
type Query {
users: [User!]!
user(id: ID!): User
posts(limit: Int): [Post!]!
}Mutations
type Mutation {
createUser(input: CreateUserInput!): User!
updateUser(id: ID!, input: UpdateUserInput!): User!
deleteUser(id: ID!): Boolean!
}Query Examples
Basic Query
query {
user(id: "123") {
name
email
}
}Nested Query
query {
user(id: "123") {
name
posts {
title
publishedAt
}
}
}Query with Arguments
query {
posts(limit: 10) {
title
author {
name
}
}
}Mutation
mutation {
createUser(input: {
name: "John Doe"
email: "john@example.com"
}) {
id
name
email
}
}Advantages over REST
Precise Data Fetching
- No over-fetching: Get exactly what’s needed
- No under-fetching: Single request for related data
- Reduced network overhead
Single Endpoint
- All operations through
/graphql - Versioning through schema evolution
- Simplified client-server communication
Strong Typing
- Compile-time query validation
- Better IDE support and tooling
- Self-documenting APIs
Real-time Capabilities
- Built-in subscriptions for live data
- WebSocket transport for real-time updates
Implementation
Popular Libraries
- Apollo Server (Node.js)
- GraphQL Yoga (Node.js)
- Strawberry (Python)
- Graphene (Python)
- Hot Chocolate (.NET)
Schema Stitching
- Combine multiple GraphQL schemas
- Federation for microservices
- Schema composition
Best Practices
Schema Design
- Use descriptive field names
- Implement proper pagination
- Handle errors consistently
- Version schema evolution
Security
- Query complexity limits
- Depth limiting
- Authentication and authorization
- Rate limiting
Performance
- Dataloader for batching
- Caching strategies
- Query optimization
- Monitoring and metrics
Detailed Topics
Schema Design
- Schema Design - Designing effective GraphQL schemas with types, interfaces, unions, and best practices
Resolvers
- Resolvers - Implementing resolver functions, data loading patterns, error handling, and performance optimization
Federation
- Federation - Schema federation for microservices, entity composition, and cross-service data management
Subscriptions
- Subscriptions - Real-time GraphQL with WebSocket connections, pub/sub patterns, and live data updates