Data Normalization in Redux — React: Redux Toolkit

Most applications work with data that has a nested structure. For example, blog posts have an author and comments. Comments also have authors and can have likes.

const blogPosts = [
  {
    id: 'post1',
    author: { username: 'user1', name: 'User 1' },
    body: '......',
    comments: [
      {
        id: 'comment1',
        author: { username: 'user2', name: 'User 2' },
        comment: '.....'
      },
      {
        id: 'comment2',
        author: { username: 'user3', name: 'User 3' },
        comment: '.....'
      }
    ]
  },
];

Working directly with such a structure is difficult for several reasons:

• It duplicates data inside it, such as author. This makes it difficult to update
• Reducer logic gets more complicated the more nesting there is

The correct approach when working with Redux is to think of it as a relational database. The data inside the store must be normalized. In this way, each slice working with a set of entities can be seen as a separate table in the database.

The basic principles of organizing data in the store:

• Each entity is stored in its own reducer.
• A collection of entities of the same type is stored as an object, where the keys are object identifiers and the values are the objects themselves.
• The order of data in this object is defined by a separate array consisting only of identifiers.
• Data refer to each other only by identifiers.

{
  posts: {
    entities: {
      post1: {
        id: 'post1',
        author: 'user1',
        body: '......',
        comments: ['comment1', 'comment2'],
      },
      post2: {
        id: 'post2',
        author: 'user2',
        body: '......',
        comments: [],
      },
    },
    ids: ['post1', 'post2'],
  },
  comments: {
    entities: {
      comment1: {
        id: 'comment1',
        author: 'user2',
        comment: '.....',
      },
      comment2: {
        id: 'comment2',
        author: 'user3',
        comment: '.....',
      },
    },
    ids: ['comment1', 'comment2'],
  },
  users: {
    entities: {
      user1: {
        id: 'user1',
        username: 'user1',
        name: 'User 1',
      },
      user2: {
        id: 'user2',
        username: 'user2',
        name: 'User 2',
      },
      user3: {
        id: 'user3',
        username: 'user3',
        name: 'User 3',
      },
    },
    ids: ['user1', 'user2', 'user3'],
  }
}

The data are now normalized. Each entity is stored in its own reducer. The entities object stores the entities themselves and the ids store the identifiers. What advantages have we gained?

• The data aren't repeated, which means that if you want to make a change, you only need to do so in one place.
• Reducers are not nested
• Data in this form are easy to retrieve and modify

Now let's see what it looks like inside the slices:

const slice = createSlice({
  name: 'users',
  initialState: {
    ids: [],
    entities: {},
  },
  reducers: {
    addUser(state, action) {
      const { user } = action.payload;

      state.entities[user.id] = user;
      state.ids.push(user.id);
    },
    removeUser(state, action) {
      const { userId } = action.payload;

      delete state.entities[userId];
      state.ids = state.ids.filter((id) => id !== userId);
    },
    updateUser(state, action) {
      const { userId, data } = action.payload;

      Object.assign(state.entities[userId], data);
    }
  },
});

dispatch(addUser({ user }));
dispatch(removeUser({ userId }));
dispatch(updateUser({ userId, data }));

normalizr

The data that come from the backend isn't usually normalized, as it's convenient for the frontend. Therefore, before adding them to the store, you must first carry out normalization. This can be done either by manually traversing the collection and converting it to the desired object, or by using the normalizr library.

Recommended materials

1. Normalizing State Shape

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