dotnet GraphQL Query generator

Given a GraphQL schema file (or a GraphQL endpoint where we can do a schema introspection), this tool will generate interfaces and classes to enable strongly typed querying from C# to a GraphQL API.

Example GraphQL schema

schema {
    query: Query
    mutation: Mutation
}

scalar Date

type Query {
	actors: [Person]
	directors: [Person]
	movie(id: Int!): Movie
	movies: [Movie]
}

type Movie {
	id: Int
	name: String
	genre: Int
	released: Date
	actors: [Person]
	writers: [Person]
	director: Person
	rating: Float
}

type Person {
	id: Int
	dob: Date
	actorIn: [Movie]
	writerOf: [Movie]
	directorOf: [Movie]
	died: Date
	age: Int
	name: String
}

type Mutation {
    addPerson(dob: Date!, name: String!): Person
}

Query Generator Command

To generate from a graphql schema file:
    dotnet run -- schema.graphql -m Date=DateTime

To generate from a live GraphQL server (note: introspection may not be supported or enabled on your server):
    dotnet run -- http://myapi.app/gql -m Date=DateTime -h "Authorization=Bearer eyAfd..."

For all command line options, use --help or -?

Both commands will generate the files GraphQLClient.cs and GeneratedTypes.cs.

GeneratedTypes.cs

Based on the example schema.graphql the GeneratedTypes.cs file will have the following content:

public interface RootQuery
{
    [GqlFieldName("actors")]
    List<Person> Actors();

    [GqlFieldName("actors")]
    List<TReturn> Actors<TReturn>(Expression<Func<Person, TReturn>> selection);

    [GqlFieldName("directors")]
    List<Person> Directors();

    [GqlFieldName("directors")]
    List<TReturn> Directors<TReturn>(Expression<Func<Person, TReturn>> selection);

    [GqlFieldName("movie")]
    Movie Movie();

    [GqlFieldName("movie")]
    TReturn Movie<TReturn>(int id, Expression<Func<Movie, TReturn>> selection);

    [GqlFieldName("movies")]
    List<Movie> Movies();

    [GqlFieldName("movies")]
    List<TReturn> Movies<TReturn>(Expression<Func<Movie, TReturn>> selection);
}

public interface Movie
{
    [GqlFieldName("id")]
    int Id { get; }
    [GqlFieldName("name")]
    string Name { get; }
    [GqlFieldName("genre")]
    int Genre { get; }
    [GqlFieldName("released")]
    DateTime Released { get; }
    [GqlFieldName("actors")]
    List<Person> Actors();
    [GqlFieldName("actors")]
    List<TReturn> Actors<TReturn>(Expression<Func<Person, TReturn>> selection);
    [GqlFieldName("writers")]
    List<Person> Writers();
    [GqlFieldName("writers")]
    List<TReturn> Writers<TReturn>(Expression<Func<Person, TReturn>> selection);
    [GqlFieldName("director")]
    Person Director();
    [GqlFieldName("director")]
    TReturn Director<TReturn>(Expression<Func<Person, TReturn>> selection);
    [GqlFieldName("rating")]
    double Rating { get; }
}

public interface Person
{
    [GqlFieldName("id")]
    int Id { get; }
    [GqlFieldName("dob")]
    DateTime Dob { get; }
    [GqlFieldName("actorIn")]
    List<Movie> ActorIn();
    [GqlFieldName("actorIn")]
    List<TReturn> ActorIn<TReturn>(Expression<Func<Movie, TReturn>> selection);
    [GqlFieldName("writerOf")]
    List<Movie> WriterOf();
    [GqlFieldName("writerOf")]
    List<TReturn> WriterOf<TReturn>(Expression<Func<Movie, TReturn>> selection);
    [GqlFieldName("directorOf")]
    List<Movie> DirectorOf();
    [GqlFieldName("directorOf")]
    List<TReturn> DirectorOf<TReturn>(Expression<Func<Movie, TReturn>> selection);
    [GqlFieldName("died")]
    DateTime Died { get; }
    [GqlFieldName("age")]
    int Age { get; }
    [GqlFieldName("name")]
    string Name { get; }
}

public interface Mutation
{
    [GqlFieldName("addPerson")]
    TReturn AddPerson<TReturn>(DateTime dob, string name, Expression<Func<Person, TReturn>> selection);
}

GraphQLClient.cs

The generated GraphQLClient class instance acts as a session to send GraphQL requests.

var httpClient = new HttpClient { BaseAddress = new Uri("http://myapi.app/gql") };
var client = new GraphQLClient(httpClient);

For custom headers like Authorization, configure them in the HttpClient. These will be used during the requests.

var httpClient = new HttpClient { BaseAddress = new Uri("http://myapi.app/") };
httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", "eyAf3s...");

var client = new GraphQLClient(new Uri("gql", UriKind.Relative), httpClient);

To use the GraphQLClient, copy the following files into your project. These will all be in the output folder:

1. GraphQLClient.cs - a simple client you can modify or extend
2. GeneratedResultTypes.cs - generated types from the schema
3. GeneratedQueryTypes.cs - extensions to allow the linq style querying
4. BaseGraphQLClient.cs - a base client that GraphQLClient inherits from
5. GqlFieldNameAttribute.cs - required by the generated code

Ideally move this to a dependency style library and tool in the future.

Request Methods

GraphQLClient exposes 2 methods:

• Query
  async Task<GqlResult<TQuery>> QueryAsync<TQuery>(Expression<Func<RootQuery, TQuery>> query)
• Mutation
  async Task<GqlResult<TQuery>> MutateAsync<TQuery>(Expression<Func<Mutation, TQuery>> query)

Query

// queries
var result = await client.QueryAsync(q => new {
    Movie = q.Movie(2, m => new {
        m.Id,
        m.Name,
        ReleaseDate = m.Released,
        Director = m.Director(d => new {
            d.Name
        })
    }),
    Actors = q.Actors(a => new {
        a.Name,
        a.Dob
    })
});

This looks similar to the GraphQL. And now result.Data is a strongly type object with the expected types.

If a field in the schema is an object (can have a selection performed on it) it will be exposed in the generated code as a method where you pass in any field arguments first and then the selection.

The GraphQL created by the above will look like this:

{
    query {
        Movie: movie(id: 2) {
            Id: id
            Name: name
            ReleaseDate: released
            Director: director {
                Name: name
            }
        }
        Actors: actors {
            Name: name
            Dob: dob
        }
    }
}

Mutations

Mutations look very similar to the above query, just as they do in GraphQL. The above schema had one mutation that can be called like so

// mutations
var mutationResult = await client.MutateAsync(m => new {
    NewPerson = m.AddPerson(new DateTime(1801, 7, 3), "John Johny", p => new { p.Id })
});

m is the Mutation type interface and lets you call any of the mutations generated from the schema. Like a query, you create a new anonymous object and call as many mutations as you wish. Each mutation method has all their arguments and the last one is a selection query on the mutation's return type.

The above has mutationResult strongly typed. E.g. mutationResult.Data.NewPerson will only have an Id field.

Input types

Any input types are generated as actual classes as the are used as arguments. The -m Date=DateTime tells the tool that the scalar type Date should be the DateTime type in C#. You can use this to support any other custom scalar types. E.g. -m Date=DateTime;Point=PointF, just comma separate a GqlScalar=DotnetType list.