Splitting our Redux Store into Multiple Slices using the createSlice Method
The Redux Toolkit has helped codify the notion that instead of splitting up your redux store into various reducer files, action files, and selector files it should be split into slices. Each slice needs to own the shape of its part of the data and is generally responsible for owning any reducers, selectors or thunks that primarily access or manipulate that information.
It's important that the shape of the data for each slice is clearly defined at the top of the file. With TypeScript this is done with an interface. With plain JavaScript you can still indicate the shape of the data by fully filling out your initialState. Even when the data is null you can add a small comment indicating the expected shape.
RTK's createSlice method simplifies the way reducers are created. Reducers are the place where the redux state gets updated (or actually replaced). An action is passed in to our redux store and each of our reducers has a chance to respond to that action with a new state. Redux reducers without RTK usually feature giant switch statements looking for different action types. With RTK you define reducer methods and the actions and action types associated with those methods are automatically generated.
In store.ts we take all of the reducers generated by these slices and combine them back together into a single redux store with each slice of data owning one key on the main data store object.
Jamund Ferguson: [0:00] In order to manage our data effectively, we're going to split up our Redux store into multiple slices.
[0:05] Slices are a fairly new concept in Redux, but they're just the way to keep your data organized. A single slice file, we usually export a reducer and any actions or selectors associated with that data. Each of our main features cart and products are going to have their own slices of the Redux store.
[0:21] First, inside of cart, create a new file called cartSlice.ts. Inside of cartSlice, type import { createSlice } from "@reduxjs/toolkit". Below that, type export interface CartState. For that, we're going to have a key of items, and it's going to have an object that has a key, which is a productID of type string and a value, which will be a number.
[0:46] An interface is the most common way to define the shape of an object with TypeScript. Here, we've defined the CartState interface, which describes what the data is going to look like in this slice of our store. This syntax right here is used to tell TypeScript to expect that our items property will be an object where the keys are productID strings and the values are numbers.
[1:06] Below that const initialState of type CartState = items with an empty object. Now type const cartSlice = createSlice. Pass in an object. First, it takes a name which we'll just call this "cart". Then we'll pass in the initialState and we can also pass in an empty reducers object, which we'll fill out later. Finally, let's export default cartSlice.reducer.
[1:28] In Redux, a reducer function processes actions passed into the Redux store, and potentially returns an updated version of the state. When we break out our store into slices, each slice gets its own reducer that handles updates for that part of the data.
[1:42] Go into your products folder and add a new file called productsSlice.ts. Inside there import { createSlice } from "@reduxjs/toolkit". We're also going to import { Product } from "../../app/api". If you remember in api.ts we make a definition for the product type based on what gets returned from our products that JSON call.
[2:07] Type export interface ProductsState { products: { [id: string] and for the value it's going to be an object of type Product. Underneath that, create your initial state with the type of ProductState, and that's going to equal an object with a key of products and a value of empty object.
[2:28] Now, type const productsSlice = createSlice. Pass in an object. First it will have a name, we'll call it products, and then we'll pass in the initialState and an empty reducers object, which we will fill out more later. Lastly, we can export default productsSlice.reducer.
[2:48] Let's go back in the store.ts and import cartReducer from "../features/cart/cartSlice" and import productsReducer from "../features/products/products Slice". Now that we've got those two reducers, we can pass them into our reducer object by typing cart: cartReducer and products: productsReducer.
[3:09] Now, even though we've split up our data into slices, we can still interact with it as one single data store.
Why don't we store the items in an array instead of an object. In a realistic app, wouldn't we store them in an array?