relayObjectType.js

const {
  GraphQLObjectType,
} = require('graphql');
const {
  fromGlobalId,
  nodeDefinitions,
} = require('graphql-relay');

const modelsRegistry = {};

const { nodeInterface, nodeField } = nodeDefinitions(
  findObjectByGlobalId, objectToGraphQLType);

function findObjectByGlobalId(globalId, { loaders }) {
  const { type, id } = fromGlobalId(globalId);
  return loaders.get(type).load(id);
}

function objectToGraphQLType(obj) {
  if (obj && obj.constructor) {
    const { modelName } = obj.constructor;
    return modelsRegistry[modelName] || null;
  }

  return null;
}

const registerModel = (graphQLObjectTypeConfig) => {
  const { name, interfaces } = graphQLObjectTypeConfig;
  if (modelsRegistry[name] === undefined) {
    modelsRegistry[name] = new GraphQLObjectType(Object.assign({},
      graphQLObjectTypeConfig, {
      interfaces: [nodeInterface].concat(interfaces || []),
    }));
  }

  return modelsRegistry[name];
};

module.exports = {
  nodeField,
  nodeInterface,
  registerModel,
};