GraphQL on C# (.NET): Complete Guide to Building Modern APIs

This book is a comprehensive guide to building modern, flexible, and efficient APIs using GraphQL on the C# (.NET) platform. Whether you are already familiar with REST but want to move to the next level of performance and convenience in client-server interaction, or are just starting your journey in backend development, this edition will become your reliable assistant.

What is this book about?

The book begins with the fundamental concepts of GraphQL: what schemas, types, queries, mutations, and subscriptions are. You will understand how GraphQL differs from REST and in which projects its use provides maximum effect. Next, the author immerses the reader in practical implementation on C#.NET using the popular Hot Chocolate library.

You will step by step create a full-fledged GraphQL server: from project setup and data type definition to integration with Entity Framework Core and databases. Special attention is paid to:

• Schema design: how to properly design a type graph so that the API is intuitive and scalable.
• Performance optimization: solving the N+1 problem, using DataLoader, batch data loading.
• Authentication and authorization: protecting endpoints, access policies at the field and type level.
• Error handling and validation: clear error messages, custom filters, and middleware.
• Testing: writing unit tests and integration tests for GraphQL resolvers.
• Real-world cases: pagination, filtering, sorting, working with files, and real-time subscriptions (WebSockets).

Who is this book for?

• .NET developers (from junior to senior) who want to master a modern approach to building APIs.
• Backend engineers who want to increase the flexibility of their services and reduce the number of client requests.
• Technical leaders and architects evaluating the implementation of GraphQL into existing infrastructure.
• Anyone interested in C# and .NET who wants to expand their technology stack with a sought-after tool.

What will you learn?

• How to set up Hot Chocolate from scratch and integrate it with ASP.NET Core.
• How to design complex graph schemas with inheritance, interfaces, and union types.
• How to efficiently work with databases via Entity Framework Core and avoid performance issues.
• How to implement real-time functionality using GraphQL subscriptions.
• How to write clean, testable resolver and middleware code.
• How to document APIs using built-in tools (Banana Cake Pop, GraphiQL).

The book contains many code examples ready to use in your projects. Each chapter ends with practical tasks to reinforce the material. This is not just theory — it is a tool that will allow you to start writing more performant and convenient APIs in C# as early as tomorrow.

From the author: "GraphQL is not just an alternative to REST. It is a philosophy that puts the client at the center of interaction. In this book, I share not only syntax but also patterns that will help you avoid typical