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Entity Adapter React: Redux Toolkit

A big part of any web application comes down to operations on entities, adding, changing, deleting, and reading them. For example, in every Hexlet lesson, you can find a discussion section and ask some questions. This section of the front end handles posts, comments, authors, and likes. Thanks to data normalization, the code for processing these entities looks identical:

const addPost = (state, post) => {
  state.entities[] = post;

const addLike = (state, like) => {
  state.entities[] = like;

We will use the same code for all other entities. Is there any way to reuse it? Of course! Redux Toolkit does this using the Entity Adapter mechanism. It provides a set of ready-made reducers and selectors for basic entity operations. First, an example:

import {
} from '@reduxjs/toolkit';

const usersAdapter = createEntityAdapter();

// By default: { ids: [], entities: {} }
const initialState = usersAdapter.getInitialState();

const slice = createSlice({
  name: 'users',
  reducers: {
    addUser: usersAdapter.addOne,
    addUsers: usersAdapter.addMany,
    removeUser: usersAdapter.removeOne,
    updateUser: usersAdapter.updateOne,

// Somewhere in the application

// By convention, the passed data must have an `id` in it to properly work
// The data are transmitted in this format: { id, changes }
dispatch(updateUser({ id:, changes: data }));
// It's enough to pass the identifier

Just four lines in the reducers brought us a full implementation of standard operations on the user. But that is not all. Besides ready-made reducers, Entity Adapter gives us a set of ready-made selectors to retrieve data from the store. To do this, they must be generated and exported from the file with the slice:

// file: usersSlice.js

// Callback defines a basic selector that extracts the desired part of the state from Redux
// For the `usersSlice`, it's `state.users`
export const selectors = usersAdapter.getSelectors((state) => state.users);

Example of its use in the application:

import { useSelector, useDispatch } from 'react-redux';

import { selectors } from '../slices/usersSlice.js';

const MyComponent = (props) => {
  // Retrieving all users as an array
  // The data from `state.users.entities` is selected internally
  // And it is sorted by `state.users.ids`
  const users = useSelector(selectors.selectAll);

  // Here's the logic of the output

In addition to the selectAll(state) we get:

  • selectIds(state) – returns ids
  • selectEntities(state) – returns entities
  • selectTotal(state) – returns the total amount
  • selectById(state, id) – returns a specific entity or undefined if it found nothing

    // The `id` is some identifier
    const user = useSelector((state) => selectors.selectById(state, id));

Recommended materials

  1. What is CRUD?
  2. The documentation of `createEntityAdapter`
  3. Creating Your Own Selectors

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