Generate TypeScript types from GraphQL schema for modular use throughout the codebase

[mattfsourcecode]

Current Situation

• Schema types are defined in src/graphql/schema/typeDefs.ts using gql from graphql-tag.
• Tests in src/__tests__/serverIntegration.test.ts use manually defined interfaces for response types.
• No shared type definitions across the application, leading to inconsistencies and duplication.

Proposed Solution

Implement @graphql-codegen/cli to generate shared TypeScript types from the GraphQL schema, ensuring type safety and consistency throughout the application.

Use Cases for Generated Types:

1. GraphQL Resolvers
   • Type-safe resolver functions with automatic parameter and return type validation.
2. Service Layer
   • Typed data manipulation and transformation operations.
3. Database Layer
   • Type alignment between the GraphQL schema and database models for safer queries and updates.
4. Middleware
   • Typed request/response handling and structured error scenarios.
5. Integration Testing
   • Type-safe test assertions and mock data generation.
6. Client-Side Code (if applicable)
   • Shared types for frontend API calls, aligning client and server logic.

Benefits

• Establishes a single source of truth for types across the application.
• Automatically generates and updates types from the GraphQL schema.
• Enhances IDE support with autocompletion and type safety.
• Reduces maintenance by eliminating manual type definitions.
• Facilitates easier refactoring with compile-time error detection.
• Improves developer productivity and reduces type-related bugs.

References

• GraphQL Code Generator Docs
• TypeScript Generator Plugin
• Resolver Plugins