@apollo/client

Fetching data with useQuery

This feature allows you to fetch data from a GraphQL server. The useQuery hook is used to execute a GraphQL query and handle loading, error, and result states.

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

const GET_LAUNCHES = gql`
  query GetLaunches {
    launches {
      id
      mission_name
    }
  }
`;

function Launches() {
  const { loading, error, data } = useQuery(GET_LAUNCHES);

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

  return data.launches.map(({ id, mission_name }) => (
    <div key={id}>
      <p>{mission_name}</p>
    </div>
  ));
}

Updating data with useMutation

This feature enables you to update data on a GraphQL server. The useMutation hook is used to execute a mutation, allowing you to create, update, or delete data.

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

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

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

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

Managing local state

This feature allows you to manage local state using Apollo Client. You can read and write to the cache as if it were a local database, enabling you to manage client-side state alongside remote data.

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

const GET_LOCAL_STATE = gql`
  query GetLocalState {
    isLoggedIn @client
  }
`;

function LoginButton() {
  const client = useApolloClient();
  const data = client.readQuery({ query: GET_LOCAL_STATE });
  const isLoggedIn = data.isLoggedIn;

  return (
    <button onClick={() => {
      client.writeQuery({
        query: GET_LOCAL_STATE,
        data: { isLoggedIn: !isLoggedIn }
      });
    }}>
      {isLoggedIn ? 'Log out' : 'Log in'}
    </button>
  );
}