Subscriptions

Relay exposes the following APIs to create subscriptions.

import { requestSubscription } from 'react-relay';

type Variables = {[name: string]: any};

type Disposable = {
  dispose(): void,
};

requestSubscription(
  environment: Environment,
  config: {
    subscription: GraphQLTaggedNode,
    variables: Variables,
    onCompleted?: ?() => void,
    onError?: ?(error: Error) => void,
    onNext?: ?(response: ?Object) => void,
    updater?: ?(store: RecordSourceSelectorProxy, data: SelectorData) => void,
    configs?: Array<DeclarativeMutationConfig>,
    cacheConfig?: CacheConfig,
  },
) => Disposable;

The function returns a Disposable on which you could call dispose() to cancel the refetch.

Now let's take a closer look at the config:

• subscription: the graphql tagged subscription query.
• variables: an object that contains the variables needed for the subscription.
• onCompleted: a callback function executed when the subscription is closed by the peer without error.
• onError: a callback function executed when Relay or the server encounters an error processing the subscription.
• onNext: a callback function executed each time a response is received from the server, with the raw GraphQL response payload.
• updater: an optional function that can supply custom logic for updating the in-memory Relay store based on the server response.
• configs: an array containing the updater configurations. It is the same as configs in commitMutation.
• cacheConfig?: Optional object containing a set of cache configuration options

Example

In a simple subscription, you only need subscription and variables. This is appropriate when you are only changing the properties of existing records that can be identified by their id:

import {
  requestSubscription,
  graphql,
} from 'react-relay';

const subscription = graphql`
  subscription MarkReadNotificationSubscription(
    $storyID: ID!
  ) {
    markReadNotification(storyID: $storyID) {
      notification {
        seenState
      }
    }
  }
`;

const variables = {
  storyID,
};

requestSubscription(
  yourEnvironment, // see Environment docs
  {
    subscription,
    variables,
    // optional but recommended:
    onCompleted: () => {
      // server closed the subscription
    },
    onError: error => console.error(error),
  }
);

Configure Network

You will need to Configure your Network layer to handle subscriptions.

Usually GraphQL subscriptions are communicated over WebSockets, here's an example using graphql-ws:

import {
    ...
    Network,
    Observable
} from 'relay-runtime';
import { createClient } from 'graphql-ws';

const wsClient = createClient({
  url:'ws://localhost:3000',
});

const subscribe = (operation, variables) => {
  return Observable.create((sink) => {
    return wsClient.subscribe(
      {
        operationName: operation.name,
        query: operation.text,
        variables,
      },
      sink,
    );
  });
}

const network = Network.create(fetchQuery, subscribe);

Alternatively, the legacy subscriptions-transport-ws library can be used too:

import {
    ...
    Network,
    Observable
} from 'relay-runtime';
import { SubscriptionClient } from 'subscriptions-transport-ws';

...

const subscriptionClient = new SubscriptionClient('ws://localhost:3000', {
    reconnect: true,
});

const subscribe = (request, variables) => {
    const subscribeObservable = subscriptionClient.request({
        query: request.text,
        operationName: request.name,
        variables,
    });
    // Important: Convert subscriptions-transport-ws observable type to Relay's
    return Observable.from(subscribeObservable);
};

const network = Network.create(fetchQuery, subscribe);

...

or if your server uses graphql-ws, this is how you would use the client in Relay:

import {
  Network,
  Observable,
  RequestParameters,
  Variables,
} from 'relay-runtime';
import { createClient } from 'graphql-ws';

const wsClient = createClient({
  url: 'wss://relayis.awesome/graphql',
});

// you can also perform queries and mutations besides the subscriptions
// through websocket, if you server allows them of course
function fetchOrSubscribe(operation: RequestParameters, variables: Variables) {
  return Observable.create((sink) => {
    if (!operation.text) {
      return sink.error(new Error('Operation text cannot be empty'));
    }
    return wsClient.subscribe(
      {
        operationName: operation.name,
        query: operation.text,
        variables,
      },
      sink
    );
  });
}

export const network = Network.create(fetchOrSubscribe, fetchOrSubscribe);

Updating the client on each response

For more complex use-cases, you may wish to perform custom logic to update Relay's in-memory cache when each subscription response is received. To do so, pass an updater function:

import { ConnectionHandler } from 'relay-runtime';

requestSubscription(
  environment,
  {
    subscription,
    variables,
    updater: store => {
      // Get the notification
      const rootField = store.getRootField('markReadNotification');
      const notification = rootField.getLinkedRecord('notification');
      // Add it to a connection
      const viewer = store.getRoot().getLinkedRecord('viewer');
      const notifications =
        ConnectionHandler.getConnection(viewer, 'notifications');
      const edge = ConnectionHandler.createEdge(
        store,
        notifications,
        notification,
        '<TypeOfNotificationsEdge>',
      );
      ConnectionHandler.insertEdgeAfter(notifications, edge);
    },
  },
);