Apollo

How to use Apollo

Apollo is a powerful tool for building GraphQL clients that provides many features out of the box. Here are some steps to get started with using Apollo:

1. Install the necessary packages: To get started, you will need to install both the

   @apollo/client
   and
   graphql
   packages. You can do this using npm, yarn or any other package manager.

2. Set up a client instance: Once you have installed the necessary packages, you can create an instance of the Apollo Client in your application. This client will be responsible for handling all of your GraphQL queries and caching the results.

Here is how you can create a new client instance:

import { ApolloClient, InMemoryCache } from '@apollo/client';

const client = new ApolloClient({
  uri: 'https://example.com/graphql',
  cache: new InMemoryCache()
});

In the above code, we are creating a new client instance using

. We are passing in a few options including the URI of our GraphQL server and an instance of which is the default caching mechanism for Apollo Client.

1. Query the server: With a client instance created, you can start making GraphQL queries. Apollo provides several ways to execute queries such as using the
   useQuery
   hook or calling the
   client.query
   method directly.

Here's an example of using the

hook to fetch a list of todos:

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

const GET_TODOS = gql`
  query {
    todos {
      id
      text
      completed
    }
  }
`;

function TodoList() {
  const { loading, error, data } = useQuery(GET_TODOS);

  if (loading) return <p>Loading...</p>;
  if (error) return <p>Error :(</p>;

  return data.todos.map(({ id, text, completed }) => (
    <div key={id}>
      <p>{text}</p>
      <p>{completed ? 'Complete' : 'Incomplete'}</p>
    </div>
  ));
}

In the above code, we are defining a GraphQL query using the

tag and then passing it to the hook from Apollo Client. The hook returns an object with the , , and properties which can be used to handle the state of the request.

1. Update data: In addition to querying data, you can also use Apollo Client to mutate data on the server. Similar to querying, there are several ways to mutate data such as using the
   useMutation
   hook or calling the
   client.mutate
   method directly.

Here's an example of using the

hook to add a new todo:

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

const ADD_TODO = gql`
  mutation AddTodo($text: String!) {
    addTodo(text: $text) {
      id
      text
      completed
    }
  }
`;

function TodoForm() {
  let input;
  const [addTodo, { data }] = useMutation(ADD_TODO);

  return (
    <form onSubmit={e => {
      e.preventDefault();
      addTodo({ variables: { text: input.value } });
      input.value = '';
    }}>
      <input ref={node => {
        input = node;
      }} />
      <button type="submit">Add Todo</button>
    </form>
  );
}

In the above code, we are defining a mutation using the

tag and then passing it to the hook from Apollo Client. The hook returns a function that can be called to execute the mutation. When the form is submitted, we call the function with the input value and reset the input field.

Conclusion: Apollo Client is a powerful tool for building GraphQL clients that provides many useful features out of the box. With Apollo, you can easily query and mutate data on the server and handle the state of your requests using hooks and cache updates.