Angular Ngrx store with multiple Arrays in state

Question

I'm trying to use Ngrx for the first time , I have been following this tutorial https://www.techiediaries.com/angular-10-ngrx-store-example/

my question is can I define my state with something like this:

export interface AppState {
    readonly firstArray: Number[];
    readonly secondArray: Number[];
    readonly thirdArray: Number[];
}

and in that case how should I implement My reducer :

export const UPDATE_DATA = 'TEMP';

export function tempReducer(state: /* How to initialize three empty arrays here ? */, action) {
  switch (action.type) {
    case TEMP:
        /*How to Update arrays here? */
    default:
        return state;
    }
}

Also is it possible to update the whole array inside the state ? (for example assign a new array to firstArray and not only add or remove elements from it)

Do yourself a favour and find an up-to-date ngrx tutorial that uses the new creator functions for actions and effects. Much easier to use, much less code. — MikeOne
– MikeOne, Commented May 22, 2021 at 14:01

David Fontes · Accepted Answer · 2021-05-22 12:59:15Z

According to what you have supplied (the tutorial source included), you have a couple of options. You could have 1 reducer for each array, as each array become part of the state (also called a slice) or you could have an object which in turn contains the 3 arrays and then use 1 reducer for that object. For the second option, you will have to manage the state of the 3 arrays (all properties) of the object in the reducer.

Below are some examples but I made some assumptions so you might have to make some adjustments.

Option 1: In your root module

imports: [
    ...
    StoreModule.forRoot({
        firstArray: firstArrayReducer,
        secondArray: secondArrayReducer,
        thirdArray: thirdArrayReducer
    });
]

Your reducer code could look like this:

export const ADD_DATA    = 'ADD';
export const UPDATE_DATA = 'UPDATE';

export function firstArrayReducer(state: YourFirstArrayType[] = [], action) {
  switch (action.type) {
    case ADD_DATA:
        // This will create a shallow copy of the array and
        // append your latest element to it
        return [...state, action.payload];
    case UPDATE_DATA:
        // Clone your array and return it with the desired modification
        const shallowClone = [...state];
        shallowClone[1] = action.payload; // This is an example
        return shallowClone;
    default:
        return state;
    }
}

Option 2: Is similar but instead of your state being a simple array, it could be an object that would in turn have the 3 arrays.

In your root module

imports: [
    ...
    StoreModule.forRoot({ objOfArrays: objArraysReducer });
]

Your reducer code could look like this:

export const ADD_DATA    = 'ADD';
export const UPDATE_DATA = 'UPDATE';

export const initialState = {
    firstArray: [],
    secondArray: [],
    thirdArray: []
};

export function objArraysReducer (state: YourObjectType = initialState, action) 
{
  // Now you need to find a way to detect what has change and update accordingly
  switch (action.type) {
    case ADD_DATA:
        // Your code...
        return state;
    default:
        return state;
    }
}

Also is it possible to update the whole array inside the state ? (for example assign a new array to firstArray and not only add or remove elements from it)

Not only it is possible as it is the desired behavior and a whole principle that NgRx are built upon. Above I used new arrays instead of mutating them.

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