platform/packages/graphql/graphql_server

graphql_server

Base package for implementing GraphQL servers. You might prefer package:angel_graphql, the fastest way to implement GraphQL backends in Dart.

package:graphql_server does not require any specific framework, and thus can be used in any Dart project.

Ad-hoc Usage

The actual querying functionality is handled by the GraphQL class, which takes a schema (from package:graphql_schema). In most cases, you'll want to call parseAndExecute on some string of GraphQL text. It returns either a Stream or Map<String, dynamic>, and can potentially throw a GraphQLException (which is JSON-serializable):

try {
    var data = await graphQL.parseExecute(responseText);

    if (data is Stream) {
        // Handle a subscription somehow...
    } else {
        response.send({'data': data});
    }
} on GraphQLException catch(e) {
    response.send(e.toJson());
}

Consult the API reference for more: https://pub.dartlang.org/documentation/graphql_server/latest/graphql_server/GraphQL/parseAndExecute.html

If you're looking for functionality like graphQLHttp in graphql-js, that is not included in this package, because it is typically specific to the framework/platform you are using. The graphQLHttp implementation in package:angel_graphql is a good example: https://github.com/angel-dart/graphql/blob/master/angel_graphql/lib/src/graphql_http.dart

Subscriptions

GraphQL queries involving subscription operations can return a Stream. Ultimately, the transport for relaying subscription events to clients is not specified in the GraphQL spec, so it's up to you.

Note that in a schema like this:

type TodoSubscription {
    onTodo: TodoAdded!
}

type TodoAdded {
    id: ID!
    text: String!
    isComplete: Bool
}

Your Dart schema's resolver for onTodo should be a Map containing an onTodo key:

field(
  'onTodo',
  todoAddedType,
  resolve: (_, __) {
    return someStreamOfTodos()
            .map((todo) => {'onTodo': todo});
  },
);

For the purposes of reusing existing tooling (i.e. JS clients, etc.), package:graphql_server rolls with an implementation of Apollo's subscriptions-transport-ws spec.

NOTE: At this point, Apollo's spec is extremely out-of-sync with the protocol their client actually expects. See the following issue to track this: https://github.com/apollographql/subscriptions-transport-ws/issues/551

The implementation is built on package:stream_channel, and therefore can be used on any two-way transport, whether it is WebSockets, TCP sockets, Isolates, or otherwise.

Users of this package are expected to extend the Server abstract class. Server will handle the transport and communication, but again, ultimately, emitting subscription events is up to your implementation.

Here's a snippet from graphQLWS in package:angel_graphql. It runs within the context of one single request:

var channel = IOWebSocketChannel(socket);
var client = stw.RemoteClient(channel.cast<String>());
var server =
    _GraphQLWSServer(client, graphQL, req, res, keepAliveInterval);
await server.done;

See graphQLWS in package:angel_graphql for a good example: https://github.com/angel-dart/graphql/blob/master/angel_graphql/lib/src/graphql_ws.dart

Introspection

Introspection of a GraphQL schema allows clients to query the schema itself, and get information about the response the server expects. The GraphQL class handles this automatically, so you don't have to write any code for it.

However, you can call the reflectSchema method to manually reflect a schema: https://pub.dartlang.org/documentation/graphql_server/latest/introspection/reflectSchema.html

Mirrors Usage

By default, dart:mirrors is not required, but it can be optionally used.

The mirrorsFieldResolver can resolve fields from concrete objects, instead of you first having to serialize them: https://pub.dartlang.org/documentation/graphql_server/latest/graphql_server.mirrors/mirrorsFieldResolver.html

You can also use convertDartType to convert a concrete Dart type into a GraphQLType. However, the ideal choice is package:graphql_generator.

• https://pub.dartlang.org/documentation/graphql_server/latest/graphql_server.mirrors/convertDartType.html
• https://pub.dartlang.org/packages/graphql_generator