Introduction to Apollo Client

Apollo Client is a comprehensive state management library for JavaScript that enables you to manage both local and remote data with GraphQL. It provides a set of features that make it easy to fetch, cache, and modify application data, improving the efficiency of your React applications.

Getting Started

  {`npm install @apollo/client graphql`}

Defining GraphQL Queries

Using Apollo Client, you can define your queries succinctly with GraphQL. Here’s an example of a simple query to fetch user data:

  {`import { gql, useQuery } from '@apollo/client';

  const GET_USER = gql\`
    query GetUser($id: ID!) {
      user(id: $id) {
        id
        name
        email
      }
    }
  \`;

  function User({ userId }) {
    const { loading, error, data } = useQuery(GET_USER, {
      variables: { id: userId },
    });

    if (loading) return 
Loading...
;
    if (error) return 
Error :(\
;

    return (
      

        
{data.user.name}
        
{data.user.email}
      
    );
  }`}

Using Mutations in Apollo Client

Mutations allow you to modify server-side data. Here’s an example of a mutation that adds a new user:

  {`import { gql, useMutation } from '@apollo/client';

  const ADD_USER = gql\`
    mutation AddUser($name: String!, $email: String!) {
      addUser(name: $name, email: $email) {
        id
        name
      }
    }
  \`;

  function AddUserForm() {
    let nameInput, emailInput;
    const [addUser, { data }] = useMutation(ADD_USER);

    return (
      

        
 {
          e.preventDefault();
          addUser({ variables: { name: nameInput.value, email: emailInput.value } });
          nameInput.value = '';
          emailInput.value = '';
        }}>
           {
              nameInput = node;
            }}
            type="text"
            placeholder="Name"
          />
           {
              emailInput = node;
            }}
            type="text"
            placeholder="Email"
          />
          Add User
        
      
    );
  }`}

Subscription Example

Subscriptions allow you to listen to real-time updates from the server. Here’s an example of a subscription to get notifications:

  {`import { gql, useSubscription } from '@apollo/client';

  const NOTIFICATIONS_SUBSCRIPTION = gql\`
    subscription OnNotificationAdded {
      notificationAdded {
        id
        message
      }
    }
  \`;

  function Notifications() {
    const { data, loading } = useSubscription(NOTIFICATIONS_SUBSCRIPTION);

    if (loading) return 
Loading...
;

    return (
      

        {data.notificationAdded.map(notification => (
          
{notification.message}
        ))}
      
    );
  }`}

Comprehensive Example

Below is a comprehensive example that integrates the above queries, mutations, and subscriptions.

  {`import React from 'react';
  import { ApolloProvider, ApolloClient, InMemoryCache, HttpLink, split } from '@apollo/client';
  import { WebSocketLink } from '@apollo/client/link/ws';
  import { getMainDefinition } from '@apollo/client/utilities';

  const httpLink = new HttpLink({
    uri: 'http://localhost:4000/graphql',
  });

  const wsLink = new WebSocketLink({
    uri: 'ws://localhost:4000/graphql',
    options: {
      reconnect: true
    }
  });

  const splitLink = split(
    ({ query }) => {
      const definition = getMainDefinition(query);
      return (
        definition.kind === 'OperationDefinition' &&
        definition.operation === 'subscription'
      );
    },
    wsLink,
    httpLink,
  );

  const client = new ApolloClient({
    link: splitLink,
    cache: new InMemoryCache()
  });

  function App() {
    return (
      
        
Apollo Client Example
        
        
        
      
    );
  }

  export default App;`}

With Apollo Client, managing your GraphQL data in React applications has never been this straightforward and efficient.

Hash: 4b28cc17a12e931ceb500e40d55a69069684edc0f1b1a43a9ebbd5d972b11660