Application: Movie Reviews
We will create an API that presents a movie and its reviews. In GraphQL, queries are used to read data, and mutations are used to create, update and delete data. To explore the CRUD operations on data, we will create two GraphQL operations as follows:
Query to fetch a movie by its identifier.Mutation to add a review to a movie.
I will not cover GraphQL Subscriptions which are a way to create and maintain a real-time connection with the GraphQL server. This feature enables the server to push instant information about related events to the client. You can read more about Subscriptions on the Apollo docs website.
Source Code
For reference, the source code of the application is available in my GitHub repository.
Set Up ASP.NET Core API Project
Create an ASP.NET Core Web Application (.NET Core) project named MovieReviews using Visual Studio or the following command:
dotnet new webapi -n MovieReviews
Let’s add the required NuGet packages to add support for GraphQL, Entity Framework Core, and Autofac in our project. For simplicity, I will use an in-memory database for persisting the movie data. You can use any database supported by Entity Framework for this purpose.
dotnet add package GraphQL
dotnet add package GraphQL.SystemTextJson
dotnet add package GraphQL.Server.Transports.AspNetCore
dotnet add package GraphQL.Server.Ui.Altair
dotnet add package Autofac
dotnet add package Microsoft.EntityFrameworkCore
dotnet add package Microsoft.EntityFrameworkCore.InMemory
We will now update the CreateHostBuilder in the class Program to use Autofac as the service provider responsible for dependency injection (DI).
public static IHostBuilder CreateHostBuilder(string[] args)
{
return Host.CreateDefaultBuilder(args)
.UseServiceProviderFactory(new AutofacServiceProviderFactory())
.ConfigureWebHostDefaults(webBuilder => { webBuilder.UseStartup<Startup>(); });
}
Create API Models
We will now define the Movie and Review models/entities for our project. Create a folder named Models and create a class file named Review in it as follows:
public class Review
{
public int Id { get; set; }
public Guid MovieId { get; set; }
public string Reviewer { get; set; }
public int Stars { get; set; }
}
Similarly, create a class file named Movie as follows:
public class Movie
{
public IList<Review> Reviews { get; set; }
public Guid Id { get; set; }
public string Name { get; set; }
public void AddReview(Review review)
{
Reviews.Add(review);
}
}
We will configure Entity Framework to operate with these entities next.
Database Setup
We will now set up the connection with the database. As I previously said, we will use the InMemory database with Entity Framework Core.
Create a folder named Database in the project, and create a class file named MovieContext in the folder. Define the code in MovieContext as follows:
public class MovieContext : DbContext
{
public MovieContext(DbContextOptions<MovieContext> options) : base(options)
{
}
public DbSet<Movie> Movie { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Movie>().OwnsMany(m => m.Reviews).HasData(
new Review
{
Id = 1,
Reviewer = "A",
Stars = 4,
MovieId = new Guid("72d95bfd-1dac-4bc2-adc1-f28fd43777fd")
},
new Review
{
Id = 2,
Reviewer = "B",
Stars = 5,
MovieId = new Guid("72d95bfd-1dac-4bc2-adc1-f28fd43777fd")
},
new Review
{
Id = 3,
Reviewer = "A",
Stars = 4,
MovieId = new Guid("c32cc263-a7af-4fbd-99a0-aceb57c91f6b")
},
new Review
{
Id = 4,
Reviewer = "D",
Stars = 5,
MovieId = new Guid("c32cc263-a7af-4fbd-99a0-aceb57c91f6b")
},
new Review
{
Id = 5,
Reviewer = "E",
Stars = 3,
MovieId = new Guid("c32cc263-a7af-4fbd-99a0-aceb57c91f6b")
},
new Review
{
Id = 6,
Reviewer = "F",
Stars = 5,
MovieId = new Guid("c32cc263-a7af-4fbd-99a0-aceb57c91f6b")
},
new Review
{
Id = 7,
Reviewer = "A",
Stars = 2,
MovieId = new Guid("7b6bf2e3-5d91-4e75-b62f-7357079acc51")
},
new Review
{
Id = 8,
Reviewer = "B",
Stars = 1,
MovieId = new Guid("7b6bf2e3-5d91-4e75-b62f-7357079acc51")
},
new Review
{
Id = 9,
Reviewer = "G",
Stars = 3,
MovieId = new Guid("7b6bf2e3-5d91-4e75-b62f-7357079acc51")
},
new Review
{
Id = 10,
Reviewer = "H",
Stars = 4,
MovieId = new Guid("7b6bf2e3-5d91-4e75-b62f-7357079acc51")
}
);
modelBuilder.Entity<Movie>().HasData(
new Movie
{
Id = new Guid("72d95bfd-1dac-4bc2-adc1-f28fd43777fd"),
Name = "Superman and Lois"
},
new Movie
{
Id = new Guid("c32cc263-a7af-4fbd-99a0-aceb57c91f6b"),
Name = "Game of Thrones"
},
new Movie
{
Id = new Guid("7b6bf2e3-5d91-4e75-b62f-7357079acc51"),
Name = "Avengers: Endgame"
}
);
}
}
Note that we added a few movies and ratings as seed data in the database. We will now register our DbContext with the application. Navigate to the Startup class and add the following code to the ConfigureServices method:
public void ConfigureServices(IServiceCollection services)
{
services
.AddEntityFrameworkInMemoryDatabase()
.AddDbContext<MovieContext>(context => { context.UseInMemoryDatabase("MovieDb"); });
}
The previous code fragment instructs Entity Framework to create an in-memory database named MovieDb. In-memory databases are great for tests, and an in-memory database will be sufficient to service our demo application.
Let’s implement the repository pattern that uses the database context to fetch a movie and add a movie review. Create an interface named IMovieRepository in the Database folder as follows.
public interface IMovieRepository
{
Task<Movie> GetMovieByIdAsync(Guid id);
Task<Movie> AddReviewToMovieAsync(Guid id, Review review);
}
Let’s implement this interface in a class named MovieRepository as follows:
public class MovieRepository : IMovieRepository
{
private readonly MovieContext _context;
public MovieRepository(MovieContext context)
{
_context = context;
_context.Database.EnsureCreated();
}
public Task<Movie> GetMovieByIdAsync(Guid id)
{
return _context.Movie.Where(m => m.Id == id).AsNoTracking().FirstOrDefaultAsync();
}
public async Task<Movie> AddReviewToMovieAsync(Guid id, Review review)
{
var movie = await _context.Movie.Where(m => m.Id == id).FirstOrDefaultAsync();
movie.AddReview(review);
await _context.SaveChangesAsync();
return movie;
}
}
We will set up dependency injection using Autofac at the end, which will make the constructor injection code functional. Let’s now start adding GraphQL support to our API, beginning with the GraphQL middleware.
GraphQL Middleware
We have already added the relevant GraphQL NuGet packages to our application. One of the packages that we installed is GraphQL.Server.Ui.Altair which provides a GraphQL UI client that helps you debug GraphQL queries and mutations. We will add the Altair UI to our application by adding the app.UseGraphQLAltair() middleware in the Configure method of the Startup class as follows:
// Enables Altair UI at path /
app.UseGraphQLAltair(new GraphQLAltairOptions {Path = "/"});
The middleware will make the Altair UI available at the default (/) endpoint.
Let’s configure the required GraphQL services in our application. Add the following code to the ConfigureServices method in the Startup class:
services
.AddGraphQL(
(options, provider) =>
{
// Load GraphQL Server configurations
var graphQLOptions = Configuration
.GetSection("GraphQL")
.Get<GraphQLOptions>();
options.ComplexityConfiguration = graphQLOptions.ComplexityConfiguration;
options.EnableMetrics = graphQLOptions.EnableMetrics;
// Log errors
var logger = provider.GetRequiredService<ILogger<Startup>>();
options.UnhandledExceptionDelegate = ctx =>
logger.LogError("{Error} occurred", ctx.OriginalException.Message);
})
// Adds all graph types in the current assembly with a singleton lifetime.
.AddGraphTypes()
// Add GraphQL data loader to reduce the number of calls to our repository. https://graphql-dotnet.github.io/docs/guides/dataloader/
.AddDataLoader()
.AddSystemTextJson();
GraphQL.NET SDK uses the builder pattern to configure the required GraphQL services. The AddGraphQL method configures certain global settings, such as the maximum depth of a query. We also configured the logger to capture and log any unhandled GraphQL exceptions.
The AddGraphTypes method scans the application’s assembly to detect the types (schema, queries, and mutations) and registers them in the DI container with a singleton lifetime.
The AddDataLoader method optimizes the calls to our repository so that data is served with as few database requests as possible. You can read more about this feature on the GraphQL.NET documentation.
GraphQL.NET supports JSON serialization of requests and responses through both System.Text.JSON and Newtonsoft.JSON. The AddSystemTextJson method instructs it to use System.Text.JSON to serialize requests and responses.
GraphQL Query
We defined the Movie and Review classes against which we want to execute a query and a mutation. However, we can’t directly use a query or a mutation on these classes. To make these classes queryable, we need to create a new type and inherit it from ObjectGraphType<T> where <T> is the type of the object that the graph represents: Movie or Review.
Create a folder named GraphQL and create another folder named Types in it. Add the MovieObject class files to the folder.
public sealed class MovieObject : ObjectGraphType<Movie>
{
public MovieObject()
{
Name = nameof(Movie);
Description = "A movie in the collection";
Field(m => m.Id).Description("Identifier of the movie");
Field(m => m.Name).Description("Name of the movie");
Field(
name: "Reviews",
description: "Reviews of the movie",
type: typeof(ListGraphType<ReviewObject>),
resolve: m => m.Source.Reviews);
}
}
Next, add the ReviewObject class file to the folder as follows:
public sealed class ReviewObject : ObjectGraphType<Review>
{
public ReviewObject()
{
Name = nameof(Review);
Description = "A review of the movie";
Field(r => r.Reviewer).Description("Name of the reviewer");
Field(r => r.Stars).Description("Star rating out of five");
}
}
Next, we will create the GraphQL schema. A schema defines the server’s API, informing the clients about the operations (query, mutation, and subscription) that the server can perform. To define our schema, create a class file named MovieReviewSchema in the GraphQL folder and populate it with the following code:
public class MovieReviewSchema : Schema
{
public MovieReviewSchema(QueryObject query, MutationObject mutation, IServiceProvider sp) : base(sp)
{
Query = query;
Mutation = mutation;
}
}
We will define the mutation operation later. Let’s begin with defining the query which is encapsulated in the QueryObject class. Create a class file named QueryObject in the GraphQL folder as follows:
public class QueryObject : ObjectGraphType<object>
{
public QueryObject(IMovieRepository repository)
{
Name = "Queries";
Description = "The base query for all the entities in our object graph.";
FieldAsync<MovieObject, Movie>(
"movie",
"Gets a movie by its unique identifier.",
new QueryArguments(
new QueryArgument<NonNullGraphType<IdGraphType>>
{
Name = "id",
Description = "The unique GUID of the movie."
}),
context => repository.GetMovieByIdAsync(context.GetArgument("id", Guid.Empty)));
}
}
We defined a query named movie that takes a GUID identifier as input, and the query resolver uses the repository’s GetMovieByIdAsync method to fetch the movie object.
GraphQL Mutation
To define a mutation operation that adds a movie review, add another graph type named ReviewInputObject in the Types folder with the following code:
public sealed class ReviewInputObject : InputObjectGraphType<Review>
{
public ReviewInputObject()
{
Name = "ReviewInput";
Description = "A review of the movie";
Field(r => r.Reviewer).Description("Name of the reviewer");
Field(r => r.Stars).Description("Star rating out of five");
}
}
Next, let’s define the mutation operation, which is encapsulated in the MutationObject graph type. Create a class file named MutationObject in the GraphQL folder as follows:
public class MutationObject : ObjectGraphType<object>
{
public MutationObject(IMovieRepository repository)
{
Name = "Mutations";
Description = "The base mutation for all the entities in our object graph.";
FieldAsync<MovieObject, Movie>(
"addReview",
"Add review to a movie.",
new QueryArguments(
new QueryArgument<NonNullGraphType<IdGraphType>>
{
Name = "id",
Description = "The unique GUID of the movie."
},
new QueryArgument<NonNullGraphType<ReviewInputObject>>
{
Name = "review",
Description = "Review for the movie."
}),
context =>
{
var id = context.GetArgument<Guid>("id");
var review = context.GetArgument<Review>("review");
return repository.AddReviewToMovieAsync(id, review);
});
}
}
Finally, we will register the schema- MovieReviewSchema using the GraphQL middleware. Please navigate to the Configure method in the Startup class and add the following code snippet to it:
app.UseGraphQL<MovieReviewSchema>();
You might have noticed that we haven’t yet defined any API controller or HTTP handler to process an incoming GraphQL request. Custom handlers are not required because the GraphQL middleware handles the incoming HTTP requests to the GrapQL endpoint. The default path to the GraphQL endpoint is /graphql. You can specify an alternate path as an argument to the UseGraphQL<T> method.
Autofac Dependency Injection Container
Finally, let’s tie everything together by configuring dependency injection in the Startup class. Create a method named ConfigureContainer, a special method used to register dependencies directly with Autofac. You don’t need to build the dependency container as it is built automatically by the AutofacServiceProviderFactory instance specified in the Program class.
public virtual void ConfigureContainer(ContainerBuilder builder)
{
builder.RegisterType<HttpContextAccessor>().As<IHttpContextAccessor>().SingleInstance();
builder.RegisterType<MovieRepository>().As<IMovieRepository>().InstancePerLifetimeScope();
builder.RegisterType<DocumentWriter>().AsImplementedInterfaces().SingleInstance();
builder.RegisterType<QueryObject>().AsSelf().SingleInstance();
builder.RegisterType<MovieReviewSchema>().AsSelf().SingleInstance();
}
Debugging
Let’s start the GraphQL server and use Altair to debug the API. Press F5 use the command dotnet run. Navigate to the base URL of your application to open the Altair UI, as shown in the figure below.
Let’s try to fetch the details of a movie using the following query:
query {
movie(id: "72d95bfd-1dac-4bc2-adc1-f28fd43777fd") {
id
name
reviews {
reviewer
stars
}
}
}
Let’s now execute the following mutation operation to add a review to the movie:
mutation addReview($review: ReviewInput!) {
addReview(id: "72d95bfd-1dac-4bc2-adc1-f28fd43777fd", review: $review) {
id
name
reviews {
reviewer
stars
}
}
}
We require a variable named review of type ReviewInput for this operation. Let’s declare the variable as follows:
{
"review": {
"reviewer": "Rahul",
"stars": 5
}
}
Execute the operation to fetch the updated movie record.
Conclusion
In this article, we covered the basics of setting up a GraphQL API with ASP.NET Core. We defined the schema using the code-first approach, defined the graph types, and wrote query/mutation resolvers to set up the API. We used the GraphQL NuGet package for .NET, which did the heavy lifting with minimal setup. We used Autofac and the repository pattern to decouple individual components and adhere to the Single Responsibility Principle (SRP). Finally, we used the Altair UI to debug the API.
I encourage you to extend the types of supported operations to output a list of movies and explore subscriptions to push new reviews to the client.
As always, I’d love to hear from you. Send in your questions or feedback in the comments section or on Twitter @rahulrai_in.
