demo.ts

import {
    createEntityAdapter,
    EntityAdapter,
    EntityState
} from "@ngrx/entity";

export interface IUser {
  id: string;
  name: string;
  email: string;
}

export interface IUserState extends EntityState<IUser>{
     // additional entities state properties
    users: [];
}

export const adapter: EntityAdapter<IUser> = createEntityAdapter<IUser>();

export const initialState: IUserState = adapter.getInitialState({
    users: []
});

export function userReducer(
    state: IUserState = initialState,
    action: UserActions
): IUserState {
    switch (action.type) {
        case UpdateUser: {
            const updatedUser = {
                id: action.payload.id,
                changes: { email: action.payload.id }
            };
            return adapter.updateOne(updatedUser, state);
        }
}

//export common use selector for your selector
export const {
    selectAll,
    selectEntities,
    selectIds,
    selectTotal
} = adapter.getSelectors();