Optimizing Data Fetching with React Query InitialData

React Query is a powerful library for managing server state in React applications. It provides hooks for fetching, caching, and updating asynchronous data without touching any global state. React Query's ability to work with initial data is one feature that makes it stand out.

What is Initial Data in React Query?

Initial data in React Query refers to the default data a query starts with before any actual data fetching occurs. This feature is handy when displaying placeholder or cached data while the fresh data is fetched from the server. React Query can render components with this data immediately by providing initial data, improving user experiences by reducing perceived loading times.

How to Use React Query InitialData

To provide initial data to a React Query hook, you can use the initialData option. This option accepts a function that returns the initial data you want to use for your query. Here is a basic example of how to use initialData:

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1import { useQuery } from 'react-query';
2import axios from 'import axios';
3
4const fetchTodo = async () => {
5  const { data } = await axios.get('/todos/1');
6  return data;
7};
8
9function TodoComponent() {
10  const { data } = useQuery('todo', fetchTodo, {
11    initialData: () => {
12      return {
13        id: 1,
14        title: 'Placeholder Title',
15      };
16    },
17  });
18
19  return <div>{data.title}</div>;
20}
21

In the above code, before the fetchTodo function is called to fetch the real data, React Query will use the object returned by the initialData function as the data for the query.

The Benefits of Using Initial Data

Using initial data can significantly enhance the performance of React applications by allowing components to render immediately with the initial data, thus improving user experiences. This is especially beneficial when the same data is being fetched multiple times, as it can be cached and reused as initial data for subsequent queries.

Managing Cached Data with React Query

React Query's sophisticated caching mechanism allows developers to manage cached data effectively. The cache is not just a simple storage; it is smart enough to handle stale data, background updates, and even provides timestamps like dataUpdatedAt to track when the data was fetched.

Here's an example of how React Query manages caching:

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1import { QueryClient, QueryClientProvider } from 'react-query';
2
3const queryClient = new QueryClient();
4
5function App() {
6  return (
7    <QueryClientProvider client={queryClient}>
8      <TodoComponent />
9    </QueryClientProvider>
10  );
11}
12

In this example, QueryClientProvider wraps the TodoComponent, allowing it to use the caching features provided by React Query.

React Query and State Management

React Query can also be considered a state management solution but primarily focuses on the server state. It allows you to manage your queries' loading, error, and data states without creating a complex state management infrastructure.

Handling Errors and Loading States

When fetching data, handling loading states and errors gracefully is essential. React Query provides built-in states for these scenarios. Here's an example of how to handle loading and error states:

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1function TodoComponent() {
2  const { data, error, isLoading } = useQuery('todo', fetchTodo, {
3    initialData: () => {
4      return {
5        id: 1,
6        title: 'Placeholder Title',
7      };
8    },
9  });
10
11  if (isLoading) {
12    return <span>Loading...</span>;
13  }
14
15  if (error) {
16    return <span>An error occurred: {error.message}</span>;
17  }
18
19  return <div>{data.title}</div>;
20}
21

In the above component, isLoading and error render different UIs based on the query's status.

Advanced Usage: Initial Query Data and QueryClient

The QueryClient can set initial query data for more advanced scenarios. This allows you to provide initial data for a query before the query is even created. Here's how you can set initial query data with QueryClient:

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1const queryClient = new QueryClient();
2
3queryClient.setQueryData('todo', {
4  id: 1,
5  title: 'Persisted Todo Title',
6});
7

Using setQueryData, you can pre-populate the cache with initial data that can be used immediately by any component that uses the todo query key.

Conclusion

React Query's initial data feature is a powerful tool for improving React applications' performance and user experience. By pre-populating queries with initial data, you can render components immediately, manage cached data effectively, and handle loading and error states gracefully. Whether you are fetching, updating, or caching data.