A Beginner’s Guide to RTK Query in Redux Toolkit

RTK Query is a modern data-fetching and caching tool that’s built into Redux Toolkit to make working with server-side data in web applications much simpler than writing your own async logic and Redux boilerplate. It’s designed to eliminate a lot of the repetitive code you’d otherwise write for fetching data, tracking loading and error states, caching responses, and updating data on the server.

At its core, RTK Query lets you define an API slice that specifies how your app should talk to a backend. From this definition it automatically generates hooks (for React), manages caching and request deduplication, and keeps your UI state in sync with server state with minimal setup.

Here’s an overview of what RTK Query is and how it works.

What RTK Query Solves

Most web apps need to fetch data from a server: loading lists of items, fetching individual records, submitting updates, etc. Traditionally in Redux you’d handle this by writing action creators, async thunks, reducers to store the data, and selectors to extract data from state. On top of that, you’d need to manage loading and error states yourself.

RTK Query abstracts all that away. You define API endpoints once and it takes care of:

Making HTTP requests to your server

Tracking loading status and errors

Caching responses and sharing cached data between components

Avoiding duplicate requests when multiple components ask for the same data

Invalidating or refetching data after mutations

All of this significantly reduces the amount of code you need to write for typical data-loading scenarios.

Defining an API with createApi

RTK Query revolves around the createApi function. You call it once to define an API slice, giving it a base URL and a set of endpoints that describe how to fetch or mutate data. For most apps you’ll use the React-specific entry point so that RTK Query generates hooks you can use directly in your components.

A basic API slice looks something like this:

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

// Create an API slice with a base URL and endpoints
export const myApi = createApi({
  reducerPath: 'myApi',
  baseQuery: fetchBaseQuery({ baseUrl: '/api' }),
  endpoints: (builder) => ({
    getItems: builder.query({
      query: () => 'items',
    }),
  }),
})

// Export the auto-generated React hook for the query
export const { useGetItemsQuery } = myApi

In this example we define a getItems endpoint that fetches from /api/items. RTK Query automatically generates a React hook useGetItemsQuery that you can call inside components to start the fetch and receive the response.

Connecting RTK Query to the Store

An API slice isn’t complete without adding it to your Redux store. The API slice includes both a reducer and middleware that manage cached data and request lifecycles. Your Redux configuration needs to look something like this:

import { configureStore } from '@reduxjs/toolkit'
import { myApi } from './services/myApi'

export const store = configureStore({
  reducer: {
    [myApi.reducerPath]: myApi.reducer,
  },
  middleware: (getDefaultMiddleware) =>
    getDefaultMiddleware().concat(myApi.middleware),
})

You also need to set up listeners so that features like refetching on reconnect work properly. RTK Query provides a helper function for that.

Using Queries in Components

Once your API slice and store are set up, using data in UI components is straightforward. Call the hook RTK Query generated for a query endpoint and it returns an object containing the data, loading status, error information, and more:

function ItemsList() {
  const { data, error, isLoading } = useGetItemsQuery()
  
  if (isLoading) return <p>Loading...</p>
  if (error) return <p>Error loading items</p>

  return (
    <ul>
      {data.map(item => (
        <li key={item.id}>{item.name}</li>
      ))}
    </ul>
  )
}

Behind the scenes RTK Query fetches the data on mount, caches it, and reruns the query only when necessary (for example when the component mounts again or arguments change).

Caching and Request Deduplication

One of the key advantages of RTK Query is its automatic caching. If multiple components request the same data, RTK Query makes only one network request and serves the cached result to all consumers. It keeps that cache updated as needed and automatically removes stale entries.

Mutations: Sending Data to the Server

In addition to queries for fetching data, RTK Query lets you define mutation endpoints for POST, PUT, DELETE, or other operations that update server data. From a mutation endpoint RTK Query generates a trigger function that you call to send the request and receive status information in return.

Using RTK Query Without React

Although most users work with the React hooks version, RTK Query’s core is UI-agnostic. You can use it with other frameworks or even plain JavaScript by dispatching thunk actions created by the API slice and subscribing to store changes manually.

When to Use RTK Query

RTK Query shines in applications that talk to an API and need to read, cache, and mutate data. If you’re already using Redux for global state, RTK Query is a natural way to handle server state too. It reduces the amount of custom code and makes data fetching more consistent and reliable.

At the same time, if your app doesn’t use Redux at all, or if your data needs are extremely simple, you might consider other libraries aimed at data fetching like React Query or SWR. RTK Query’s close integration with Redux makes it especially powerful for apps that already use Redux Toolkit.

Summary

RTK Query simplifies the process of fetching and managing server data in Redux applications. It lets you define a central API slice, automatically generates hooks for use in your UI, handles caching and request logic for you, and integrates seamlessly with Redux Toolkit. By taking the guesswork out of data fetching and reducing boilerplate, it lets developers focus more on building features and less on wiring up API logic.