Integrating C# with GraphQL: A Guide for Developers

Integrating C# with GraphQL: A Guide for Developers


GraphQL, a query language for APIs, and runtime for executing those queries, has gained significant popularity due to its efficiency and flexibility. It offers a more precise and powerful alternative to traditional REST APIs. C# can be used to implement GraphQL APIs.

This post explores how C# developers can integrate GraphQL into their applications, enhancing data retrieval and manipulation capabilities.

Understanding GraphQL and Its Advantages

Before diving into the integration, it’s essential to understand what GraphQL is and why it’s beneficial. GraphQL allows clients to request only the data they need, reducing over-fetching and under-fetching issues common in REST APIs.

This efficiency is crucial for performance, especially in complex applications or those with limited bandwidth.

Setting Up GraphQL in a C# Environment

To integrate GraphQL with a C# application, you will need a GraphQL server. Popular choices include GraphQL.NET and Hot Chocolate. These libraries enable you to define a GraphQL schema and set up a server in your C# application.

  1. Install the GraphQL Library: Use NuGet package manager to install a GraphQL library like GraphQL.NET.
  2. Define Your Schema: Create types and fields that represent your data model.
  3. Set Up the GraphQL Server: Configure the server to handle GraphQL requests.

GraphQL.NET is a popular library for working with GraphQL in the C# programming environment.

Here’s a brief overview of how GraphQL.NET integrates with C#:

  1. Defining a Schema: In GraphQL.NET, the schema is defined using C#. This schema specifies the types available in the data graph, along with the queries and mutations (operations to fetch and modify data, respectively) that can be performed. The schema is central to a GraphQL API, acting as a contract between the server and the client.
  2. Creating Types: You define object types that correspond to the data you want to expose. Each type can include fields, and these fields can return simple scalars (like int or string), complex objects, lists, etc. These types mirror the structure of the data in your backend (like database entities) and determine what the client can query.
  3. Resolvers: For each field in your types, you need to define resolvers. A resolver is a piece of logic that knows how to fetch or compute the value for that field. In C#, this often involves writing methods that might, for instance, query a database or call another service.
  4. Handling Queries and Mutations: Clients send queries to request data and mutations to modify data. In GraphQL.NET, you’ll define query and mutation classes, which are collections of fields. The fields correspond to the operations clients can perform, and each field has a resolver.
  5. Integration with ASP.NET Core: GraphQL.NET can be integrated with ASP.NET Core, providing a way to host your GraphQL API. The integration allows for features like middleware support, dependency injection, and more, making it seamless to incorporate GraphQL into modern web applications.
  6. Execution: When a request is made to a GraphQL server, the GraphQL.NET library parses the query, validates it against the schema, and executes it by calling the appropriate resolvers. The result is then returned to the client in the requested format, typically JSON.
  7. Tooling and Extensions: GraphQL.NET supports various tools and extensions, such as graphical UIs for testing queries (like GraphiQL or Playground), subscription support for real-time data updates, and integration with popular ORMs like Entity Framework for database interactions.
  8. Performance Considerations: One of the challenges in implementing a GraphQL API is efficiently handling queries, especially when they involve complex data fetching and nested queries. GraphQL.NET offers features like DataLoader to batch and cache requests, minimizing database roundtrips.

Let’s dive into a more detailed explanation of GraphQL.NET with example code snippets to illustrate how it’s used in a C# environment. GraphQL.NET provides a way to define a GraphQL schema and serve it over HTTP, typically within an ASP.NET Core application.

Setting Up the Project

First, you need to add the GraphQL.NET NuGet package to your C# project. You can do this via the NuGet Package Manager or the command line:

dotnet add package GraphQL 
dotnet add package GraphQL.Server.Ui.Playground

Defining a Schema

In GraphQL.NET, you define your schema in C#. Here’s a simple example:

public class StarWarsSchema : Schema 

    public StarWarsSchema(IServiceProvider provider) : base(provider
        Query = provider.GetRequiredService<StarWarsQuery>(); 

public classStarWarsQuery : ObjectGraphType 

    public StarWarsQuery() 
        Field<StringGraphType>("hero", resolve: context => "R2-D2"); 

This code defines a basic schema with one query type, StarWarsQuery, which has a single field hero that resolves to a string.

Creating Object Types

Suppose you have a Droid type in your data model. You would define it like this:

public class DroidType : ObjectGraphType<Droid> 

    public DroidType() 
        Field(x => x.Id).Description("The id of the droid."); 
        Field(x => x.Name).Description("The name of the droid."); 

public class Droid 

    public string Idgetset; } 
    public string Namegetset; } 
    // Other properties... 

Expanding the Query Class

You can expand the StarWarsQuery class to include more complex queries:

public class StarWarsQuery : ObjectGraphType 

    public StarWarsQuery() 
        argumentsnew QueryArguments(new QueryArgument<StringGraphType> 
        resolve: context => 

            var id = context.GetArgument<string>("id"); 
            return new Droid { Id = id, Name"R2-D2" }; 

Setting Up a GraphQL Endpoint in ASP.NET Core

In your Startup.cs, you need to set up the GraphQL endpoint:

public void ConfigureServices(IServiceCollection services
    services.AddGraphQL((options, provider) => 
      var logger = provider.GetRequiredService<ILogger<Startup>>(); 
      options.UnhandledExceptionDelegate = ctx => logger.LogError("{Error} occurred",   ctx.OriginalException.Message); 

public void Configure(IApplicationBuilder app, IWebHostEnvironment env
    app.UseGraphQLPlayground(optionsnew GraphQLPlaygroundOptions()); 

Executing a Query

Clients can now send a GraphQL query to your endpoint to fetch data. For example, a query to get the name of a droid by its ID might look like this:

    droid(id"1") { name } 

The server will execute this query against your StarWarsSchema, resolving the droid field by calling the corresponding resolver in StarWarsQuery.


Integrating GraphQL with C# enhances your application’s data handling capabilities, providing a more efficient and flexible way to work with APIs. By following the steps outlined, developers can set up a GraphQL server in a C# environment, create effective queries and mutations, and ensure their API is robust and performant.

Remember, the key to a successful implementation is thorough testing and optimisation. Paying attention to these points will lead to a more reliable and efficient GraphQL API in your C# applications.


Hi, my name is Stephen Finchett. I have been a software engineer for over 30 years and worked on complex, business critical, multi-user systems for all of my career. For the last 15 years, I have been concentrating on web based solutions using the Microsoft Stack including ASP.Net, C#, TypeScript, SQL Server and running everything at scale within Kubernetes.