Tutorial

In this tutorial, we will build a game using GraphQL mutations. The goal of the game is to find a hidden treasure in a grid of 9 squares. We will give players three tries to find the treasure. This should give us an end-to-end look at Relay – from the GraphQL schema on the server, to the React application on the client.

Warm up #

Let's start a project using the Relay Starter Kit as a base.

git clone https://github.com/relayjs/relay-starter-kit.git relay-treasurehunt
cd relay-treasurehunt
npm install

A simple database #

We need a place to hide our treasure, a way to check hiding spots for treasure, and a way to track our turns remaining. For the purposes of this tutorial, we'll hide these data in memory.

/**
 * ./data/database.js
 */

// Model types
export class Game {}
export class HidingSpot {}

// Mock data
const game = new Game();
game.id = '1';

const hidingSpots = [];
(function() {
  let hidingSpot;
  const indexOfSpotWithTreasure = Math.floor(Math.random() * 9);
  for (let i = 0; i < 9; i++) {
    hidingSpot = new HidingSpot();
    hidingSpot.id = `${i}`;
    hidingSpot.hasTreasure = (i === indexOfSpotWithTreasure);
    hidingSpot.hasBeenChecked = false;
    hidingSpots.push(hidingSpot);
  }
})();

let turnsRemaining = 3;

export function checkHidingSpotForTreasure(id) {
  if (hidingSpots.some(hs => hs.hasTreasure && hs.hasBeenChecked)) {
    return;
  }
  turnsRemaining--;
  const hidingSpot = getHidingSpot(id);
  hidingSpot.hasBeenChecked = true;
}
export function getHidingSpot(id) {
  return hidingSpots.find(hs => hs.id === id);
}
export function getGame() { return game; }
export function getHidingSpots() { return hidingSpots; }
export function getTurnsRemaining() { return turnsRemaining; }

What we have written here is a mock database interface. We can imagine hooking this up to a real database, but for now let's move on.

Authoring a schema #

A GraphQL schema describes your data model, and provides a GraphQL server with an associated set of resolve methods that know how to fetch data. We will use graphql-js and graphql-relay-js to build our schema.

Let's open up the starter kit's schema, and replace the database imports with the ones we just created:

/**
 * ./data/schema.js
 */

/* ... */

import {
  Game,
  HidingSpot,
  checkHidingSpotForTreasure,
  getGame,
  getHidingSpot,
  getHidingSpots,
  getTurnsRemaining,
} from './database';

At this point, you can delete everything up until queryType in ./data/schema.js.

Next, let's define a node interface and type. We only need to provide a way for Relay to map from an object to the GraphQL type associated with that object, and from a global ID to the object it points to:

const {nodeInterface, nodeField} = nodeDefinitions(
  (globalId) => {
    const {type, id} = fromGlobalId(globalId);
    if (type === 'Game') {
      return getGame(id);
    } else if (type === 'HidingSpot') {
      return getHidingSpot(id);
    } else {
      return null;
    }
  },
  (obj) => {
    if (obj instanceof Game) {
      return gameType;
    } else if (obj instanceof HidingSpot) {
      return hidingSpotType;
    } else {
      return null;
    }
  }
);

Next, let's define our game and hiding spot types, and the fields that are available on each.

const gameType = new GraphQLObjectType({
  name: 'Game',
  description: 'A treasure search game',
  fields: () => ({
    id: globalIdField('Game'),
    hidingSpots: {
      type: hidingSpotConnection,
      description: 'Places where treasure might be hidden',
      args: connectionArgs,
      resolve: (game, args) => connectionFromArray(getHidingSpots(), args),
    },
    turnsRemaining: {
      type: GraphQLInt,
      description: 'The number of turns a player has left to find the treasure',
      resolve: () => getTurnsRemaining(),
    },
  }),
  interfaces: [nodeInterface],
});

const hidingSpotType = new GraphQLObjectType({
  name: 'HidingSpot',
  description: 'A place where you might find treasure',
  fields: () => ({
    id: globalIdField('HidingSpot'),
    hasBeenChecked: {
      type: GraphQLBoolean,
      description: 'True if this spot has already been checked for treasure',
      resolve: (hidingSpot) => hidingSpot.hasBeenChecked,
    },
    hasTreasure: {
      type: GraphQLBoolean,
      description: 'True if this hiding spot holds treasure',
      resolve: (hidingSpot) => {
        if (hidingSpot.hasBeenChecked) {
          return hidingSpot.hasTreasure;
        } else {
          return null;  // Shh... it's a secret!
        }
      },
    },
  }),
  interfaces: [nodeInterface],
});

Since one game can have many hiding spots, we need to create a connection that we can use to link them together.

const {connectionType: hidingSpotConnection} =
  connectionDefinitions({name: 'HidingSpot', nodeType: hidingSpotType});

Now let's associate these types with the root query type.

const queryType = new GraphQLObjectType({
  name: 'Query',
  fields: () => ({
    node: nodeField,
    game: {
      type: gameType,
      resolve: () => getGame(),
    },
  }),
});

With the queries out of the way, let's start in on our only mutation: the one that spends a turn by checking a spot for treasure. Here, we define the input to the mutation (the id of a spot to check for treasure) and a list of all of the possible fields that the client might want updates about after the mutation has taken place. Finally, we implement a method that performs the underlying mutation.

const CheckHidingSpotForTreasureMutation = mutationWithClientMutationId({
  name: 'CheckHidingSpotForTreasure',
  inputFields: {
    id: { type: new GraphQLNonNull(GraphQLID) },
  },
  outputFields: {
    hidingSpot: {
      type: hidingSpotType,
      resolve: ({localHidingSpotId}) => getHidingSpot(localHidingSpotId),
    },
    game: {
      type: gameType,
      resolve: () => getGame(),
    },
  },
  mutateAndGetPayload: ({id}) => {
    const localHidingSpotId = fromGlobalId(id).id;
    checkHidingSpotForTreasure(localHidingSpotId);
    return {localHidingSpotId};
  },
});

Let's associate the mutation we just created with the root mutation type:

const mutationType = new GraphQLObjectType({
  name: 'Mutation',
  fields: () => ({
    checkHidingSpotForTreasure: CheckHidingSpotForTreasureMutation,
  }),
});

Finally, we construct our schema (whose starting query type is the query type we defined above) and export it.

export const Schema = new GraphQLSchema({
  query: queryType,
  mutation: mutationType
});

Processing the schema #

Before going any further, we need to serialize our executable schema to JSON for use by the Relay.QL transpiler, then start up the server. From the command line:

npm run update-schema
npm start

Writing the game #

Let's tweak the file ./js/routes/AppHomeRoute.js to anchor our game to the game root field of the schema:

export default class extends Relay.Route {
  static queries = {
    game: () => Relay.QL`query { game }`,
  };
  static routeName = 'AppHomeRoute';
}

Next, let's create a file in ./js/mutations/CheckHidingSpotForTreasureMutation.js and create subclass of Relay.Mutation called CheckHidingSpotForTreasureMutation to hold our mutation implementation:

import Relay from 'react-relay';

export default class CheckHidingSpotForTreasureMutation extends Relay.Mutation {
  static fragments = {
    game: () => Relay.QL`
      fragment on Game {
        id,
        turnsRemaining,
      }
    `,
    hidingSpot: () => Relay.QL`
      fragment on HidingSpot {
        id,
      }
    `,
  };
  getMutation() {
    return Relay.QL`mutation{checkHidingSpotForTreasure}`;
  }
  getCollisionKey() {
    return `check_${this.props.game.id}`;
  }
  getFatQuery() {
    return Relay.QL`
      fragment on CheckHidingSpotForTreasurePayload @relay(pattern: true) {
        hidingSpot {
          hasBeenChecked,
          hasTreasure,
        },
        game {
          turnsRemaining,
        },
      }
    `;
  }
  getConfigs() {
    return [{
      type: 'FIELDS_CHANGE',
      fieldIDs: {
        hidingSpot: this.props.hidingSpot.id,
        game: this.props.game.id,
      },
    }];
  }
  getVariables() {
    return {
      id: this.props.hidingSpot.id,
    };
  }
  getOptimisticResponse() {
    return {
      game: {
        turnsRemaining: this.props.game.turnsRemaining - 1,
      },
      hidingSpot: {
        id: this.props.hidingSpot.id,
        hasBeenChecked: true,
      },
    };
  }
}

Finally, let's tie it all together in ./js/components/App.js:

import CheckHidingSpotForTreasureMutation from '../mutations/CheckHidingSpotForTreasureMutation';
import React from 'react';
import Relay from 'react-relay';

class App extends React.Component {
  _getHidingSpotStyle(hidingSpot) {
    let color;
    if (this.props.relay.hasOptimisticUpdate(hidingSpot)) {
      color = 'lightGrey';
    } else if (hidingSpot.hasBeenChecked) {
      if (hidingSpot.hasTreasure) {
        color = 'blue';
      } else {
        color = 'red';
      }
    } else {
      color = 'black';
    }
    return {
      backgroundColor: color,
      cursor: this._isGameOver() ? null : 'pointer',
      display: 'inline-block',
      height: 100,
      marginRight: 10,
      width: 100,
    };
  }
  _handleHidingSpotClick(hidingSpot) {
    if (this._isGameOver()) {
      return;
    }
    this.props.relay.commitUpdate(
      new CheckHidingSpotForTreasureMutation({
        game: this.props.game,
        hidingSpot,
      })
    );
  }
  _hasFoundTreasure() {
    return (
      this.props.game.hidingSpots.edges.some(edge => edge.node.hasTreasure)
    );
  }
  _isGameOver() {
    return !this.props.game.turnsRemaining || this._hasFoundTreasure();
  }
  renderGameBoard() {
    return this.props.game.hidingSpots.edges.map(edge => {
      return (
        <div
          key={edge.node.id}
          onClick={this._handleHidingSpotClick.bind(this, edge.node)}
          style={this._getHidingSpotStyle(edge.node)}
        />
      );
    });
  }
  render() {
    let headerText;
    if (this.props.relay.getPendingTransactions(this.props.game)) {
      headerText = '\u2026';
    } else if (this._hasFoundTreasure()) {
      headerText = 'You win!';
    } else if (this._isGameOver()) {
      headerText = 'Game over!';
    } else {
      headerText = 'Find the treasure!';
    }
    return (
      <div>
        <h1>{headerText}</h1>
        {this.renderGameBoard()}
        <p>Turns remaining: {this.props.game.turnsRemaining}</p>
      </div>
    );
  }
}

export default Relay.createContainer(App, {
  fragments: {
    game: () => Relay.QL`
      fragment on Game {
        turnsRemaining,
        hidingSpots(first: 9) {
          edges {
            node {
              hasBeenChecked,
              hasTreasure,
              id,
              ${CheckHidingSpotForTreasureMutation.getFragment('hidingSpot')},
            }
          }
        },
        ${CheckHidingSpotForTreasureMutation.getFragment('game')},
      }
    `,
  },
});

A working copy of the treasure hunt can be found in the relay-examples repository.

Now that we've gone through this tutorial, let's dive into what it means to build a GraphQL client framework and how this compares to clients for more traditional REST systems.