Part 75: Updating React Query Cache: Seamlessly Synchronize UI State After Login

[Pages] React Query

[Pages] React Query

In modern web applications, ensuring that the UI accurately reflects the current state of the user's session is crucial for maintaining a seamless user experience. One common challenge developers face is updating UI components after a user logs in, especially when cached data is involved. In this blog post, we'll explore how to use React Query's caching mechanism to update UI components immediately after a login event, without unnecessary network requests.

The Problem: Stale Cache Data

Imagine you're building an application where the user needs to log in to access personalized features. After implementing the login functionality using React Query's useMutation, you notice a peculiar issue: the NavBar doesn't immediately reflect the user's logged-in state. Instead, it shows the user as logged out until the page is refreshed or the cache expires. This happens because the user data is cached with a staleTime, causing the NavBar to use outdated data.

The Solution: Direct Cache Manipulation

To solve this issue, we can directly manipulate the React Query cache using the useQueryClient hook. This allows us to update the cached data immediately after a successful login, ensuring the NavBar reflects the correct user state without waiting for the cache to expire or requiring a page reload.

Implementing Cache Updates in SignInPage

Let's see how we can modify the SignInPage component to update the user cache after a successful login:

// File: pages/sign-in.js

import { useRouter } from 'next/router';
import { useState } from 'react';
import { useMutation, useQueryClient } from 'react-query';
import Button from '../components/Button';
import Field from '../components/Field';
import Input from '../components/Input';

function SignInPage() {
  const router = useRouter();
  const [email, setEmail] = useState('');
  const [password, setPassword] = useState('');
  const queryClient = useQueryClient();

  const mutation = useMutation(() => fetchJson('/api/login', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ email, password }),
  }));

  const handleSubmit = async (event) => {
    event.preventDefault();
    try {
      const user = await mutation.mutateAsync();
      queryClient.setQueryData('user', user);
      console.log('signed in:', user);
      router.push('/');
    } catch (err) {
      // Handle error
    }
  };

  return (
    <form onSubmit={handleSubmit}>
      <Field label="Email">
        <Input
          typeemail"
          value={email}
          onChange={(event) => setEmail(event.target.value)}
        />
      </Field>
      <Field label="Password">
        <Input
          type="password"
          value={password}
          onChange={(event) => setPassword(event.target.value)}
        />
      </Field>
      {mutation.isError && (
        <p className="text-red-700">
          Invalid credentials
        </p>
      )}
      {mutation.isLoading ? (
        <p>Loading...</p>
      ) : (
        <Button type="submit">Sign In</Button>
      )}
    </form>
  );
}

export default SignInPage;

Key Changes and Benefits

1. Using useQueryClient: By importing and using the useQueryClient hook, we gain access to the query client instance, which allows us to manipulate the cache directly.

2. Updating Cache with setQueryData: After a successful login, we call queryClient.setQueryData('user', user). This updates the cache with the new user data, ensuring that any component using this data reflects the updated state immediately.

3. No Additional Network Requests: By updating the cache, we avoid making additional requests to the user API route, leveraging the data returned by the login request instead.

Testing the Changes

To confirm the effectiveness of these changes, follow these steps:

1. Sign Out: Ensure that you are signed out.

2. Sign In: Use the correct credentials to sign in.

3. Observe the NavBar: Notice how the NavBar immediately reflects the logged-in state without additional requests to the user API.

Conclusion

By directly manipulating the React Query cache, you can ensure that your application's UI remains up-to-date with the latest user session state, providing a seamless experience. This approach eliminates unnecessary network requests, optimizes performance, and enhances the user experience. With these techniques, you'll be well-equipped to handle similar challenges in your own React applications.