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Apollo Client (React)

Overview

You can use Apollo Client to connect to your Realm app’s exposed GraphQL API from a React application. Apollo Client runs queries and mutations, maintains a client-side data cache, and integrates into your app with idiomatic React components and hooks.

See a Working Demo Application

Check out the MongoDB Realm GraphQL - Apollo (React) repository on GitHub to see a fully set-up React & Apollo application that’s ready to connect to your own MongoDB Realm app. It uses the sample_mflix.movies collection that’s included in the MongoDB Atlas sample data sets.

If you don’t want to clone the repository, the demo application is also available in-browser in the Realm GraphQL CodeSandbox.

Set Up Apollo Client

1

Install Dependencies

As in any MongoDB Realm project, you’ll need to install the Realm Web SDK to authenticate users and requests.

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npm install realm-web

Apollo bundles the core components that you need to create a client in a package called @apollo/client. It also requires the graphql package to parse GraphQL queries.

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npm install @apollo/client graphql

2

Create an Apollo GraphQL Client

Create a new ApolloClient object that points to your Realm app’s GraphQL API endpoint. You generate the endpoint URL based on your Realm App ID or find it on the GraphQL page of the Realm UI.

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import * as Realm from "realm-web";
import { ApolloClient, HttpLink, InMemoryCache } from "@apollo/client";

export const APP_ID = "<Your App ID>";
const graphql_url = `https://realm.mongodb.com/api/client/v2.0/app/${APP_ID}/graphql`;

const client = new ApolloClient({
  link: new HttpLink({ uri: graphql_url }),
  cache: new InMemoryCache(),
});

3

Set Up User Authentication

The ApolloClient is configured to send requests to your app. However, all Realm GraphQL requests must include a valid user access token to authenticate requests, so right now any operations sent from Apollo will fail.

To authenticate requests, you need to add an Authorization header with a valid Realm user access token to each GraphQL request.

You can authenticate a user and get their access token with the Realm Web SDK. The Apollo HttpLink object allows you to add custom headers to every request by defining a custom fetch function.

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// Connect to your MongoDB Realm app
const app = new Realm.App(APP_ID);

// Get a valid Realm user access token to authenticate requests
async function getValidAccessToken() {
  if (!app.currentUser) {
    // If no user is logged in, log in an anonymous user
    await app.logIn(Realm.Credentials.anonymous());
  } else {
    // The logged in user's access token might be stale,
    // Refreshing custom data also refreshes the access token
    await app.currentUser.refreshCustomData();
  }
  // Get a valid access token for the current user
  return app.currentUser.accessToken;
}

const client = new ApolloClient({
  link: new HttpLink({
    uri: graphql_url,
    fetch: async (uri, options) => {
      const accessToken = await getValidAccessToken();
      options.headers.Authorization = `Bearer ${accessToken}`;
      return fetch(uri, options);
    },
  }),
  cache: new InMemoryCache()
});

4

Add the Apollo Client to Your App

The Apollo client object is now configured to send authenticated GraphQL requests to your MongoDB Realm app. All that’s left to do is make it available to the rest of your React application.

The @apollo/client package exports an ApolloProvider component that makes the client available to any Apollo hooks that you call from child components. Wrap your app in an ApolloProvider and pass the client object to the provider.

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import React from "react";
import { render } from "react-dom";
import App from "./App";
import {
  ApolloProvider,
  ApolloClient,
  HttpLink,
  InMemoryCache
} from "@apollo/client";

// ... code to create the GraphQL client

render(
  <ApolloProvider client={client}>
    <App />
  </ApolloProvider>,
  document.getElementById("root"),
);

Run Queries and Mutations

The @apollo/client package includes a set of declarative React hooks that connect your components to the GraphQL API and handle query and mutation execution.

To define queries and mutations that you can pass to the hooks, install graphql-tag:

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npm install graphql-tag

Apollo Hooks Must Have An ApolloProvider

Components that call the query and mutation hooks must be descendants of the ApolloProvider that you configured for your MongoDB Realm app. The hooks call the query and mutation methods on the provided client object.

Run a Query

Apollo Client includes two hooks for executing queries. The hooks accept identical parameters but differ in when they execute the query:

• useQuery() runs automatically when its component mounts. It also returns a callback that re-runs the query whenever you call it.
• useLazyQuery() returns a callback function that executes the query whenever you call it. It does not run the query on component mount.

Both hooks accept a query definition and additional options, including variables that Apollo passes to the query. They also both return information about the query’s current execution status and data returned from the most recent execution.

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import React from "react";
import { useQuery } from "@apollo/client";
import gql from "graphql-tag";
import MovieList from "./MovieList"

// Must be rendered inside of an ApolloProvider
export default function Movies() {
  const { loading, error, data } = useQuery(gql`
    query AllMovies {
      movies {
        _id
        title
        year
        runtime
      }
    }
  `);
  if(loading) {
    return <div>loading</div>
  }
  if(error) {
    return <div>encountered an error: {error}</div>
  }
  return <MovieList movies={data.movies} />
}

Run a Mutation

The useMutation() hook accepts a mutation definition and an optional configuration object. The most common option you’ll need to pass is a variables object that maps to GraphQL variables in the mutation definition.

The hook returns several objects in an array:

• a callback function that executes the mutation
• an object that includes information on the mutation’s execution status and data returned from the most recent execution.

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import React from "react";
import { useMutation } from "@apollo/client";
import gql from "graphql-tag";

// Must be rendered inside of an ApolloProvider
export default function MovieList({ movies }) {
  const [updateMovieTitle] = useMutation(gql`
    mutation UpdateMovieTitle($oldTitle: String!, $newTitle: String!) {
      updateOneMovie(query: { title: $oldTitle }, set: { title: $newTitle }) {
        title
        year
      }
    }
  `);
  return (
    <ul>
      {movies.map((movie) => (
        <li key={movie._id}>
          <div>{movie.name}</div>
          <button
            onClick={() =>
              updateMovieTitle({
                variables: {
                  oldTitle: movie.title,
                  newTitle: "Some New Title",
                },
              })
            }
          >
            Update Title
          </button>
        </li>
      ))}
    </ul>
  );
}

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