Using GraphQL with .NET

Introduction

GraphQL is a query language for APIs that allows clients to request only the data they need. In this tutorial, we will explore how to use GraphQL with .NET to build efficient and flexible APIs.

Prerequisites

Before we begin, ensure you have the following:

• .NET SDK installed
• Visual Studio or Visual Studio Code (optional)
• Basic understanding of C# and ASP.NET Core

Setting Up the Project

Create a new ASP.NET Core project and configure GraphQL.

dotnet new webapi -n GraphQLDemo
cd GraphQLDemo
dotnet add package GraphQL.Server.Transports.AspNetCore
dotnet add package GraphQL.Server.Ui.Playground

Defining GraphQL Schema

Define a GraphQL schema that specifies types and queries.

Example GraphQL Schema

// GraphQL/Schema.cs
public class GraphQLSchema : Schema
{
    public GraphQLSchema(IServiceProvider provider) : base(provider)
    {
        Query = provider.GetRequiredService<GraphQLQuery>();
        // Mutation = provider.GetRequiredService<GraphQLMutation>(); // Uncomment for mutations
    }
}

Implementing GraphQL Queries

Create GraphQL queries to fetch data.

Example GraphQL Query

// GraphQL/Queries/GraphQLQuery.cs
public class GraphQLQuery : ObjectGraphType
{
    public GraphQLQuery()
    {
        Field<StringGraphType>(
            "hello",
            resolve: context => "world"
        );
    }
}

Configuring GraphQL Middleware

Add GraphQL middleware to the ASP.NET Core pipeline.

Example Middleware Configuration

// Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddSingleton<GraphQLQuery>();
    services.AddSingleton<GraphQLSchema>();
    services.AddGraphQL(options =>
    {
        options.EnableMetrics = true;
        options.ExposeExceptions = true;
    })
    .AddSystemTextJson();
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    // other configurations
    app.UseRouting();
    app.UseEndpoints(endpoints =>
    {
        endpoints.MapControllers();
        endpoints.MapGraphQL();
    });
}

Testing GraphQL Queries

Test GraphQL queries using tools like GraphQL Playground.

Conclusion

In this tutorial, we explored how to use GraphQL with .NET to build efficient and flexible APIs. We defined a GraphQL schema, implemented GraphQL queries, configured GraphQL middleware in an ASP.NET Core application, and tested GraphQL queries. By adopting GraphQL, you can simplify API development and improve client-server interactions in your .NET applications.