mmgerald/relay

A toolset for creating Relay.js compatible GraphQL servers in dotnet.

GraphQL.Relay

A collection of classes, tools, and utilities for creating Relay.js compatible GraphQL servers in dotnet.

Usage

Setup

Add the Nuget package:

$> dotnet add package GraphQL.Relay

Ensure your resolver for GraphQL can resolve:

• ConnectionType<>
• EdgeType<>
• NodeInterface
• PageInfoType

If you're using the resolver from MVC (IServiceProvider), that might look like this:

services.AddTransient(typeof(ConnectionType<>));
services.AddTransient(typeof(EdgeType<>));
services.AddTransient<NodeInterface>();
services.AddTransient<PageInfoType>();

GraphTypes

Included are a few GraphQL types and helpers for creating Connections, Mutations, and Nodes

QueryGraphType

A top level Schema query type, which defines the required node root query;

public class StarWarsQuery : QueryGraphType
{
  public StarWarsQuery() {
    Field<DroidType>(
      "hero",
      resolve: context => new Droid { DroidId = "1", Name = "R2-D2" }
    );
  }
}

public class StarWarsSchema : Schema
{
  public StarWarsSchema() {
    Query = new StarWarsQuery();
  }
}

NodeGraphType<TSource, TOut>, NodeGraphType<TSource>, NodeGraphType

NodeTypes, are ObjectGraphTypes that implement the NodeInterface and provide a GetById method, which allows Relay (via the node() Query) to refetch nodes when it needs to.

Nodes, also provide a convenient Id() method for defining global id fields, derived from the type Name and Id. If your underlying type has a name conflict on the field id, the "local" Id will be prefixed with the type name, e.g. Droid.Id -> droidId

public class Droid
{
  public string DroidId { get; set; }
  public string Name { get; set; }
}

public class DroidType : NodeGraphType<Droid>
{
  public DroidType()
  {
    Name = "Droid";

    Id(d => d.DroidId); // adds an id Field as well as the `Droid` id field

    Field<StringGraphType>("name", "The name of the droid.");
  }

  public override Droid GetById(string droidId) {
    return StarWarsData.GetDroidByIdAsync(droidId);
  }
}

Mutations

Relay mutations specify a few constraints on top of the general GraphQL mutations. To accompodate this, there are mutation specific GraphTypes provided.

MutationGraphType

The top level mutation type attached to the GraphQL Schema

public class StarWarsMutation : MutationGraphType
{
  public StarWarsMutation() {

    Mutation<CreateDroidInput, CreateDroidPayload>("createDroid");
    Mutation<DeleteDroidInput, DeleteDroidPayload>("deleteDroid");
  }
}

public class StarWarsSchema : Schema
{
  public StarWarsSchema() {
    Query = new StarWarsQuery();
    Mutation = new StarWarsMutation();
  }
}

MutationInputGraphType

An simple base class that defines a clientMutationId field. functionally identical to InputObjectGraphType otherwise

MutationPayloadGraphType<TSource, TOut>, MutationPayloadGraphType<TSource>, MutationPayloadGraphType

The output ObjectGraphType containing the mutation payload, functionally similar to an ObjectGraphType with the addition of requiing a MutateAndGetPayload() method used to resolve the payload from the inputs.

public class CreateDroidPayload : MutationPayloadGraphType<DroidPayload, Task<DroidPayload>>
{
  public CreateDroidPayload()
  {
    Name = "CreateDroidPayload";

    Field(
      name: "droid",
      type: typeof(Droid));
  }

  public override async Task<DroidPayload> MutateAndGetPayload(MutationInputs inputs)
  {
    string name = inputs.Get<string>("name");

    Droid newDroid = await StarWarsData.CreateDroidAsync(name)

    return new DroidPayload {
      Droid = newDroid
    };
  }
}

Connections

Luckily GraphQL-dotnet already provides helpful utilities for creating connection fields, on GraphTypes. In addition included here are a few more helpful methods for creating relay compatible Connections from IEnumerables.

Connection.ToConnection(IEnumerable items, ResolveConnectionContext context)

Creates a connection from an existing list of objects.

public class Droid
{
  public string DroidId { get; set; }
  public string Name { get; set; }
  public IEnumerable<Droid> Friends { get; set; }
}

public class DroidType : ObjectGraphType<Droid>
{
  public DroidType()
  {
    Name = "Droid";

    Field<StringGraphType>("name", "The name of the droid.");

    Connection<DroidType>()
      .Name("friends")
      .Resolve(context =>
        Connection.ToConnection(c.Source.Friends, context));
  }
}

Connection.ToConnection(IEnumerable items, ResolveConnectionContext context, int sliceStartIndex, int totalCount)

Similar to the above, but creates a connection with the correct cursors, when you only have a slice of the entire set of items. Windowing the items based on the arguments.

Connection.CursorToOffset(string cursor)

Convert a connection item cursor to the int index of the item in the set.

Connection.OffsetToCursor(int offset)

Convert an index offset to a connection cursor.