Types of parameters 'action' and 'action' are incompatible, Property 'payload' is missing In Angular ngrx

Question

I am new to angular. Here I using ngrx to manage a state in my angular app. But when I'm compiling I got the following error. It says that 'Types of parameters 'action' and 'action' are incompatible'. I want to know the reason for this and how to solve this?

 
    Error: src/app/shopping-list/store/shoppingList.actions.ts:9:5 - error TS2564: Property 'payload' has no initializer and is not definitely assigned in the constructor.
    
    9     payload: Ingredient;
          ~~~~~~~
    src/app/app.module.ts:25:27 - error TS2322: Type '(state: { ingredients: Ingredient[]; } | undefined, action: AddIngredient) => { ingredients: Ingredient[]; }' is not assignable to type 'ActionReducer<{ ingredients: Ingredient[]; }, Action>'.
      Types of parameters 'action' and 'action' are incompatible.
        Property 'payload' is missing in type 'Action' but required in type 'AddIngredient'.
    
    25     StoreModule.forRoot({ shoppingList: shoppingListReducer }),
                                 ~~~~~~~~~~~~
    
      src/app/shopping-list/store/shoppingList.actions.ts:9:5
        9     payload: Ingredient;
              ~~~~~~~
        'payload' is declared here.

This is my shoppingList.actions.ts file.

import { Action } from '@ngrx/store'

import { Ingredient } from '../../shared/ingredient.model';

export const ADD_INGREDIENT = 'ADD_INGREDIENT';

export class AddIngredient implements Action {
    readonly type = ADD_INGREDIENT;
    payload: Ingredient;
}

This is the shoppingList.reducer.ts file.

import { Ingredient } from "src/app/shared/ingredient.model";

import * as shoppingListActions from './shoppingList.actions';

const intialState = {
    ingredients: [
        new Ingredient("Apples", 3),
        new Ingredient("Tomatoes", 4)
    ]
}

export function shoppingListReducer(state = intialState, action: shoppingListActions.AddIngredient) {
    switch (action.type) {
        case shoppingListActions.ADD_INGREDIENT:
            return {
                ...state,
                ingredients: [...state.ingredients, action.payload]
            }
        default:
            return state;
    }
}

Here is my app.module.ts file.

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { AppRouting } from './app-routing.module';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';
import { HttpClientModule } from '@angular/common/http';
import { StoreModule } from '@ngrx/store';

import { AppComponent } from './app.component';
import { HeaderComponent } from './header/header.component';
import { SharedModule } from './shared/shared.module';
import { CoreModule } from './core.module';
import { shoppingListReducer } from './shopping-list/store/shoppingLis.reducer';

@NgModule({
  declarations: [
    AppComponent,
    HeaderComponent,

  ],
  imports: [
    BrowserModule,
    FormsModule,
    ReactiveFormsModule,
    HttpClientModule,
    StoreModule.forRoot({ shoppingList: shoppingListReducer }),
    AppRouting,
    SharedModule,
    CoreModule,
  ],
  bootstrap: [AppComponent]
})
export class AppModule { }

Answer 1

Your problem is because of signature issue,

Method StoreModule.forRoot<unknown, Action>(reducers: ActionReducerMap<unknown, Action>)

Technically you are passing a correct parameter but still it is saying that your Action object parameter contains a field call payload which is not present in Action parameter of ActionReducerMap<unknown, Action>. Technically it should not be an error as you have already inherited Action to your action class

class AddIngredient implements Action{

but unfortunately it is clear that Action in ActionReducerMap<unknown, Action> is not from '@ngrx/store' or they are not same, and therefore giving the compilation error.

As you don't have any other option, you have to fix it like below:-

First create your State like below in your shopping-list.reducer.ts

export interface ShoppingListState{
    ingredients: Ingredient[];
}

const initialState: ShoppingListState = {
    ingredients: [
        new Ingredient('Apples', 5),
        new Ingredient("Tomatoes", 4),
    ]
};

Also modify your reducer method like below:-

export function shoppingListReducer(state: ShoppingListState = initialState, 
    action: shoppingListActions.AddIngredient): ShoppingListState {
    switch(action.type){

Now create a file call index.ts ( in the same location of reducer file - you can provide a different name as well) like below under your action folder

import { ShoppingListState,  shoppingListReducer } from './shopping-list.reducer';
import { ActionReducerMap } from '@ngrx/store';


export const rootReducer = {};

export interface AppState {
    shoppingList: ShoppingListState;
};


export const reducers: ActionReducerMap<AppState, any> = {
    shoppingList: shoppingListReducer
};

Now import this reducers to your app.module.ts

import { reducers } from './reducers/'

and modify your code like below

StoreModule.forRoot(reducers)

Also try to avoid declaration of variable like below.

payload: Ingredient;

better use constructor and modify your code like below:-

export class AddIngredient implements Action {
    readonly type = ADD_INGREDIENT;
    constructor(public payload: Ingredient){}
}

Hope this will fix your issue.