Network Layer

In order to know how to access your GraphQL server, Relay Modern requires developers to provide an object implementing the NetworkLayer interface when creating an instance of a Relay Environment. The environment uses this network layer to execute queries, mutations, and (if your server supports them) subscriptions. This allows developers to use whatever transport (HTTP, WebSockets, etc) and authentication is most appropriate for their application, decoupling the environment from the particulars of each application's network configuration.

Currently the easiest way to create a network layer is via a helper from the relay-runtime package:

import {
  Environment,
  Network,
  RecordSource,
  Store,
} from 'relay-runtime';

// Define a function that fetches the results of an operation (query/mutation/etc)
// and returns its results as a Promise:
function fetchQuery(
  operation,
  variables,
  cacheConfig,
  uploadables,
) {
  return fetch('/graphql', {
    method: 'POST',
    headers: {
      // Add authentication and other headers here
      'content-type': 'application/json'
    },
    body: JSON.stringify({
      query: operation.text, // GraphQL text from input
      variables,
    }),
  }).then(response => {
    return response.json();
  });
}

// Create a network layer from the fetch function
const network = Network.create(fetchQuery);
const store = new Store(new RecordSource())

const environment = new Environment({
  network,
  store
  // ... other options
});

export default environment;

Note that this is a basic example to help you get started. This example could be extended with additional features such as request/response caching (enabled e.g. when cacheConfig.force is false) and uploading form data for mutations (the uploadables parameter).

Caching

Relay modern makes no assumptions about what to cache and will garbage collect any data that is no longer referenced.

You have to implement your own cache strategy. A simple solution is to use QueryResponseCache (an in-memory cache):

import {
  Environment,
  Network,
  QueryResponseCache,
  RecordSource,
  Store,
} from 'relay-runtime';

const oneMinute = 60 * 1000;
const cache = new QueryResponseCache({ size: 250, ttl: oneMinute });

function fetchQuery(
  operation,
  variables,
  cacheConfig,
) {
  const queryID = operation.text;
  const isMutation = operation.operationKind === 'mutation';
  const isQuery = operation.operationKind === 'query';
  const forceFetch = cacheConfig && cacheConfig.force;

  // Try to get data from cache on queries
  const fromCache = cache.get(queryID, variables);
  if (
    isQuery &&
    fromCache !== null &&
    !forceFetch
  ) {
    return fromCache;
  }

  // Otherwise, fetch data from server
  return fetch('/graphql', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      query: operation.text,
      variables,
    }),
  }).then(response => {
    return response.json();
  }).then(json => {
    // Update cache on queries
    if (isQuery && json) {
      cache.set(queryID, variables, json);
    }
    // Clear cache on mutations
    if (isMutation) {
      cache.clear();
    }

    return json;
  });
}

const environment = new Environment({
  network: Network.create(fetchQuery),
  store: new Store(new RecordSource()),
});

export default environment;

Custom open-source implementations

react-relay-network-modern on npm - is a Network Layer for Relay Modern which has built-in highly customizable middlewares for commonly used scenarios: batching query requests, caching, authentication, request retrying, logging. Moreover, you may write your own middlewares with custom logic.