anomepani/DotNetGraphQLQueryGen

Generate dotnet interfaces/classes from a GraphQL schema to perform type-safe querying from dotnet

dotnet GraphQL Query generator

Given a GraphQL schema file, this tool will generate interfaces and classes to enable strongly typed querying from C# to a GraphQL API.

Example, given the following 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
}

Running dotnet run -- schema.graphql -m Date=DateTime will generate the following

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);
}

It also generates a GraphQLClient class that will work for an unauthenticated API. You can modify that class to implement the authentication you may need. GraphQLClient exposes 2 methods, async Task<GqlResult<TQuery>> QueryAsync<TQuery>(Expression<Func<RootQuery, TQuery>> query) for queries and async Task<GqlResult<TQuery>> MutateAsync<TQuery>(Expression<Func<Mutation, TQuery>> query) for mutations.

Example usage

var client = new GraphQLClient();
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 protected on to 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 anaoymous 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 seperate a GqlScalar=DotnetType list.