React Query's useMutation hook

How to Use React Query's useMutation Hook: A Detailed Guide

React Query is an excellent library for managing server-side state in your React application. One of the most powerful hooks React Query offers is the useMutation hook, used for handling side effects like POST and DELETE requests. In this guide, we’ll walk through the process of setting up and using the useMutation hook with detailed code snippets to make sure you're comfortable integrating it into your projects.

Setting Up Basic Functions

Before we dive into the useMutation hook, let’s create placeholder functions that will handle our mutation logic. In this case, we’ll create three key functions: getExistingTour, generateTourResponse, and createNewTour.

export const getExistingTour = ({ city, country }) => {
    return null;  // Placeholder for checking existing tours in the database
};

export const generateTourResponse = ({ city, country }) => {
    return null;  // Placeholder for generating a tour response
};

export const createNewTour = ({ tour }) => {
    return null;  // Placeholder for creating and saving a new tour
};

        

These functions are initially placeholders, returning null just for the example

Integrating the useMutation Hook

Now that we have our basic functions, let’s start integrating the useMutation hook. First, we'll need to import useMutation and useQueryClient from React Query. These will handle our mutation and manage the client-side cache.

import { useMutation, useQueryClient } from 'react-query';
import { getExistingTour, generateTourResponse, createNewTour } from './utils';

const queryClient = useQueryClient();

const { mutate, isPending } = useMutation(async (destination) => {
    const newTour = await generateTourResponse(destination);
    
    if (newTour) {
        return newTour;  // Return the newly created tour
    } else {
        throw new Error('No matching city found');
    }
}, {
    onSuccess: () => {
        queryClient.invalidateQueries('tours');  // Invalidate and refetch the tours data
    },
    onError: (error) => {
        console.error(error.message);
    }
});

        

In this example, we're using useMutation to generate a new tour response. If successful, we return the tour data; otherwise, an error is thrown. On success, the invalidateQueries function is used to refresh the cached tours data, ensuring our UI stays updated.

Handling the Mutation Response

Once the mutation function has executed, we can manage its state (pending, success, or failure) using the isPending flag and other response handlers. Here's how we can toggle UI behavior based on the mutation's progress.

const handleSubmit = (destination) => {
    mutate(destination);
};

return (
    < div >
        {isPending ? (
            < span className="loading">Loading...< /span >
        ) : (
            < form onSubmit={handleSubmit}>
                < input type="text" placeholder="Enter city" / >
                < button type="submit">Generate Tour< /button>
            < /form >
        )}
    < /div >
);

        

In this case, while the mutation is pending, we display a loading indicator. Once the mutation is completed, we either show the form again or handle the new tour data accordingly.

Advanced Logic and Error Handling

In practice, you’ll often need more complex logic within your mutation. You can use additional checks to determine whether a new tour already exists in the database before proceeding. Here's a more advanced example:

const mutationFunction = async (destination) => {
    const existingTour = await getExistingTour(destination);

    if (existingTour) {
        return existingTour;
    } else {
        const newTour = await createNewTour(destination);
        return newTour;
    }
};

        

This setup checks if a tour already exists before creating a new one, streamlining your mutation logic and avoiding unnecessary database entries.

Important: Always remember to handle errors gracefully when using useMutation. You can use error states or toast notifications to inform users about issues like invalid inputs or server errors.

Final Thoughts

The useMutation hook is incredibly powerful for handling side effects in your React Query-powered applications. By properly managing your functions, responses, and UI, you can create a seamless user experience even when dealing with asynchronous operations.

As you expand your use of React Query, continue to explore its capabilities with hooks like useQuery and useQueryClient for an optimized data-fetching experience.