What is the difference between useQuery and useMutation hooks in React Query, and what scenarios are they suitable for?

In React Query, useQuery and useMutation are two core hooks with distinct purposes and use cases:

useQuery

Functionality: Used for performing read-only operations, such as fetching data.

Suitable scenarios:

• Fetching list data (e.g., user lists, product lists)
• Fetching detail data (e.g., user details, order details)
• Any scenario where you need to read data from the server without modifying it

Features:

• Automatically caches data
• Supports data invalidation and background refreshing
• Returns data, loading state, error state, etc.
• Can configure retry strategies

Basic usage:

javascript
const { data, isLoading, error } = useQuery('todos', fetchTodos);

useMutation

Functionality: Used for performing write operations, such as creating, updating, or deleting data.

Suitable scenarios:

• Submitting form data
• Updating user information
• Deleting resources
• Any scenario where you need to modify server data

Features:

• Supports optimistic updates
• Can configure success/failure callbacks
• Supports request cancellation
• Can trigger refetching of related queries

Basic usage:

javascript
const mutation = useMutation(addTodo, {
  onSuccess: () => {
    // Success callback, e.g., refetch data
    queryClient.invalidateQueries('todos');
  },
});

// Calling method
mutation.mutate(newTodo);

Core differences

1. Operation type: useQuery for read operations, useMutation for write operations
2. Caching behavior: useQuery automatically caches data, useMutation doesn't cache results
3. Calling method: useQuery executes automatically (configurable), useMutation requires manual call to mutate method
4. Return values: useQuery returns data and states, useMutation returns mutation function and states

Using these two hooks correctly can effectively manage data fetching and modification operations in your application, improving development efficiency and user experience.