Overview

GraphQL follows a layered architecture where a query from the client is executed against a schema, resolved through functions, and mapped to underlying data sources.

Core Components

1. Client
   • Sends queries/mutations
   • Defines required data shape
   • Example: iOS app using a GraphQL client
2. Schema
   • Defines available types, fields, and operations
   • Acts as a contract between client and server
3. Resolvers
   • Functions that fetch/compute data for each field
   • Connect schema fields to actual data sources
4. Execution Engine
   • Parses and validates queries
   • Calls resolvers
   • Constructs response
5. Data Sources
   • Database (SQL/NoSQL)
   • REST APIs
   • External services

Request Flow

1. Client sends query
2. Server parses query → converts to AST
3. Validates query against schema
4. Execution engine calls resolvers
5. Resolvers fetch data from sources
6. Response is assembled and returned

Example Flow

Query