GraphQL

    GraphQL: {
      typeDefs: `
        """Soccer Player"""
        type Player implements Node {
          id: ID!
          email: String!
          name: String!
          photoURL: String
          position: String
          """A team player belongs to"""
          team: Team
        }

        extend type Query {
          """Current Player"""
          viewer: Player
          player(id: ID!): Player
        }

        extend type Subscription {
          playerMessage: String!
          playerUpdated: Player
        }
      `,

      resolvers: {

        Player: {

          team: {
            call: {
              action: "team.get",
              params: {
                id: "@source.teamId",
              },
            },
          },

          position: `({ source, args, context, info }) => source.position.toUpperCase()`,
`

          // be noted that special field __isTypeOf got only three arguments
          __isTypeOf: `({ source, context, info }) => return source.someSpecialFieldForThisType != null`,

          // be noted that special field __resolveType got only three arguments
          __resolveType: `
            ({ source, context, info }) => {
              if (source.someSpecialFieldForThisType != null) {
                return "TypeA";
              } else {
                return "TypeB";
              }
            }
          `,
        },

        Query: {
          viewer: {
            call: {
              action: "player.get",
              params: {
                id: "@context.user.player.id[]",
              },
            },
          },
          player: {
            call: {
              action: "player.get",
              params: {
                id: "@args.id[]",
              },
            },
          },
        },

query {
  viewer {
    id
    email
  }
  one: player(id: 1) {
    id
    email
  }
  two: player(id: 2) {
    id
    email
  }
  three: player(id: 3) {
    id
    email
  }
}

        Subscription: {
          playerMessage: {
            subscribe: {
              events: ["player.message"],
            },
          },

          playerMessage: {
            subscribe: {
              events: ["player.message"],
              map: `({ source, args, context, info }) => source.payload.message`,
            },
          },
        },
      },
    },