React Query Update Cache Strategies For Better Data Handling

Managing server state in React apps can get tricky, but React Query simplifies the process. It handles data fetching, caching, and updates, so you don’t have to manage everything manually.

This blog breaks down how to update the React Query cache using key concepts like query keys, mutation responses, and cached data. You’ll also learn about advanced techniques, including cache management, handling multiple mutations, and using optimistic updates.

React Query for State Management

React Query leverages a query cache mechanism to store data fetched from the server and uses a query key to uniquely identify each data entry. Developers can create a custom hook that encapsulates this logic, ensuring that different components across a page can interact with the same cached data without unnecessary refetches.

Key Hooks and Their Responsibilities

Hook	Responsibility	Example Usage
useQuery	Fetches and caches data using a unique query key	useQuery('todos', fetchTodos)
useMutation	Manages the mutation response and mutation state	const mutation = useMutation(updateTodo)

Note: The empty array is often used as a default value for the cache if no data is available.

Sample Code: Fetching Data in a Component

1import React from 'react';
2import { useQuery } from 'react-query';
3
4function Todos() {
5  // The query key 'todos' uniquely identifies this cached query
6  const { data = [], error, isLoading } = useQuery('todos', async () => {
7    // Simulate an async request to a database
8    const response = await fetch('/api/todos');
9    return response.json();
10  });
11
12  if (isLoading) return <div>Loading...</div>;
13  if (error) return <div>Error loading todos.</div>;
14
15  return (
16    <ul>
17      {data.map((todo) => (
18        <li key={todo.id}>{todo.title}</li>
19      ))}
20    </ul>
21  );
22}

​

In this example, React Query automatically handles the query cache with the query key 'todos', ensuring that cached data is available to any component that needs it. Developers should assume that if data is not present, the value defaults to an empty array.

Handling Mutation Responses and Optimistic Updates

React Query simplifies the process of updating server state by offering powerful tools like useMutation . This hook not only handles mutation responses but also supports optimistic updates to instantly reflect changes on the screen.

Optimistic Update Strategy

When performing a mutation, React Query allows you to modify the cache directly before receiving the final response from the server. This is achieved using callbacks like onMutate and the onSuccess callback (onSuccess) as the last argument in the configuration object.

1. onMutate: Modify the cache immediately.

2. onError: Roll back the cached data if the mutation fails.

3. onSuccess: Execute a callback when the mutation response is successful.

4. onSettled: Trigger query invalidation to refresh the server state.

Sample Code: Optimistic Update with useMutation

1import React from 'react';
2import { useMutation, useQueryClient } from 'react-query';
3
4function UpdateTodo({ newTodo }) {
5  const queryClient = useQueryClient();
6
7  const mutation = useMutation(updateTodo, {
8    // onMutate is called before the mutation function executes.
9    onMutate: async (newTodo) => {
10      // Cancel any outgoing refetches (so they don't overwrite our optimistic update)
11      await queryClient.cancelQueries('todos');
12      const previousTodos = queryClient.getQueryData('todos') || [];
13
14      // Modify the cache directly by appending the newTodo to the cached data array.
15      queryClient.setQueryData('todos', (old) => [...old, newTodo]);
16      console.log('Optimistic update applied', newTodo);
17      // Return context with the previous value
18      return { previousTodos };
19    },
20    onError: (err, newTodo, context) => {
21      // Roll back the cache if mutation fails.
22      queryClient.setQueryData('todos', context.previousTodos);
23      console.error('Mutation failed, rolled back changes');
24    },
25    // The onSuccess callback ensures any post-mutation response logic is executed.
26    onSuccess: (data) => {
27      console.log('Mutation response received:', data);
28    },
29    // onSettled invalidates the query to ensure the cached data is in sync with the server state.
30    onSettled: () => {
31      queryClient.invalidateQueries('todos');
32    },
33  });
34
35  // Return useMutation instance for further use
36  return (
37    <div>
38      <form
39        onSubmit={(e) => {
40          e.preventDefault();
41          // Use the mutate method to trigger the mutation
42          mutation.mutate(newTodo);
43        }}
44      >
45        <input type="text" name="title" placeholder="Todo title" required />
46        <button type="submit">Submit</button>
47      </form>
48    </div>
49  );
50}

​

In this example, the developer demonstrates a complete use case where a component submits a post to update a database. The mutation function uses several callbacks:

• onMutate to update the query cache immediately,

• onError to revert changes if an error occurs,

• onSuccess as a callback to log the mutation response, and

• onSettled to perform query invalidation.

This logic ensures that cached data is updated optimistically, giving the user immediate feedback while maintaining the integrity of the server state.

Advanced Cache Management Techniques

The React Query cache (or QueryCache) is a core part of React Query's design. It holds the cached data, meta information, and the status of each query. Advanced techniques focus on updating this cache immutably and efficiently without causing unnecessary refetches.

Immutability in Cache Updates

Using methods like setQueryData requires that the cached data be updated in an immutable manner. This ensures that React Query can properly detect changes and update the component views accordingly. Here’s an example:

1// Updating the cache in one line while ensuring immutability
2queryClient.setQueryData('todos', (oldData = []) =>
3  oldData.map((todo) =>
4    todo.id === updatedTodo.id ? { ...todo, ...updatedTodo } : todo
5  )
6);

​

Note: Always log the context when performing such operations to verify that variables and arguments are processed correctly.

Flow of Mutation and Cache Update

This diagram outlines the logic flow where:

• A user action triggers the mutation,

• The cache is updated optimistically (using multiple mutations if needed),

• The server returns a mutation response,

• The React Query cache is updated immutably, and

• Query invalidation is performed to sync with the database.

The Bottom Line!

To build a smooth and responsive application, developers should focus on:

• Efficient state management using React Query with clear query keys.

• Leveraging optimistic updates and mutation responses to update the cache directly.

• Implementing custom hooks that import and encapsulate React Query logic for different components.

• Using callbacks like onMutate, onSuccess, and onSettled as the last argument to handle mutation events.

• Ensuring cached data is updated immutably to avoid bugs, particularly when dealing with an empty array or undefined values.

• Understanding the use case of handling async data fetches and post requests that modify the server state.

By integrating these strategies, you can create components that not only fetch and display data effectively on the screen but also log important details, manage error states, and maintain a consistent client state across the page. This approach keeps your application efficient, user-friendly, and robust.

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