React Query is a powerful library for managing state and data fetching in React applications. One of its key features is its ability to handle asynchronous data fetching and caching. In this blog post, we’ll explore how React Query simplifies data fetching by providing a convenient state management solution. This article was inspired and informed by the following post: Thinking in React Query.

The Basics

At its core, React Query is a state manager. It doesn’t make web requests itself but rather relies on promises to handle data fetching. This means that you can use React Query with any web request package as long as it returns a promise, such as Axios.

One of the main advantages of using React Query is that it allows you to maintain a single source of truth for your data. There’s no need to store the fetched data in additional state variables. React Query takes care of caching the data and ensuring that it’s always up to date.

Managing Data Staleness

React Query introduces the concept of data staleness, which is the amount of time before data is considered outdated. You can set the staleTime option to define the duration after which data is considered stale. By default, React Query performs a new network request only if the data is stale. Otherwise, it uses the cached data without making another query.

Here’s an example of using React Query with Axios to fetch and cache data:

import { useQuery } from 'react-query';
import axios from 'axios';

const fetchUser = () => axios.get('/api/user');

function UserProfile() {
  const { data } = useQuery('user', fetchUser, { staleTime: 30000 });

  return (
    <div>
      <h1></h1>
      <p></p>
      <!-- Display user profile -->
    </div>
  );
}

In this example, the useQuery hook is used to fetch the user data using the fetchUser function. The ‘user’ argument is the query key, which uniquely identifies this query and is used for caching purposes.

The { staleTime: 30000 } option specifies that the data will be considered stale after 30 seconds (30,000 milliseconds). If the data is stale, React Query will automatically trigger a new network request to refresh the data.

Managing Query Dependencies

React Query allows you to specify additional query parameters by adding them to the query key. This makes the parameters dependencies, ensuring that different parameter values are stored with different keys in the cache. If a dependency changes, React Query will refresh the cache and perform a new network request.

Consider the following example:

import { useQuery } from 'react-query';
import axios from 'axios';

const fetchPosts = (userId) => axios.get(`/api/posts?userId=${userId}`);

function UserPosts({ userId }) {
  const { data } = useQuery(['posts', userId], () => fetchPosts(userId));

  return (
    <div>
      <!-- Display user posts -->
    </div>
  );
}

In this case, the query key [‘posts’, userId] includes both the ‘posts’ identifier and the userId parameter. React Query ensures that different userId values are stored with different keys in the cache. If the userId changes, React Query will automatically update the cache and perform a new network request.

Conclusion

React Query simplifies data fetching and state management in React applications. By leveraging promises and caching mechanisms, React Query provides a convenient solution for handling asynchronous data.