RTK Query

RTK Query is a library built into Redux Toolkit (RTK) that provides developers with a set of tools to simplify data fetching and caching. It's an abstraction over the Redux store that automatically manages caching, re-fetching, and state updates related to remote data fetching. Before RTK Query, developers would often manually manage asynchronous actions, reducers, and state for API requests using a combination of redux-thunk or redux-saga with the base Redux Toolkit functions. RTK Query aims to reduce the boilerplate and complexity associated with this.

Here's a breakdown of RTK Query's main features and benefits:

1. Automatic Caching: RTK Query will cache your data by default. This means that if you fetch the same data again, RTK Query will serve it from the cache rather than making a redundant API call.
2. Automatic Re-fetching: You can configure RTK Query to automatically re-fetch data at certain intervals or when the application refocuses.
3. Automatic State Management: RTK Query auto-generates reducers and actions for your API calls, so you don't have to write any Redux boilerplate.
4. Optimistic Updates: It supports optimistic updates, which can provide a faster perceived loading time for users by updating the UI before the API call resolves.
5. Polling: You can easily set up polling for endpoints that need to refresh data at regular intervals.
6. Hooks Integration: RTK Query provides React hooks out of the box, making it easy to fetch, cache, and update data in your components.
7. Request Lifecycle: RTK Query defines the lifecycle of a request, including actions for when a request starts, succeeds, or fails. This makes it easy to handle loading states and errors in your UI.
8. Normalization: While not built directly into RTK Query, it's designed to work seamlessly with normalized data and integrates well with libraries like normalizr.

Basic Example:

Suppose you want to fetch a list of todos from an API. Here's how you could set it up with RTK Query:

Create an API Slice:

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import { createApi, fetchBaseQuery } from '@reduxjs/toolkit/query/react';

export const api = createApi({
  baseQuery: fetchBaseQuery({ baseUrl: '/api' }),
  endpoints: (builder) => ({
    getTodos: builder.query<Array<Todo>, void>({
      query: () => 'todos',
    }),
  }),
});

export const { useGetTodosQuery } = api;

Use the Generated Hook in a Component:

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import React from 'react';
import { useGetTodosQuery } from './todosApiSlice';

const TodoList = () => {
  const { data: todos, isLoading, isError } = useGetTodosQuery();

  if (isLoading) return <div>Loading...</div>;
  if (isError) return <div>Error loading todos</div>;

  return (
    <ul>
      {todos?.map(todo => (
        <li key={todo.id}>{todo.title}</li>
      ))}
    </ul>
  );
};

In this example, by defining an endpoint in the createApi call, RTK Query auto-generates a hook (useGetTodosQuery) that we can use directly in our components to fetch data, handle loading states, and more.