ngrx-normalizing-state-after.ts

// State
export interface State {
  customers: { [id: string]: Customer };
  selectedCustomerId: string;
}

// Reducer
export function reducer(state, action) {
  switch (action.type) {
    ...
    case EDIT_CUSTOMER:
      return {
        ...state,
        customers: {
          ...state.customers,
          [action.payload.id]: action.payload,
        },
      };
    ...
  }
}

// Selectors
export const selectCustomers = createSelector(
  selectCustomersState,
  state => Object.keys(state.customers).map(id => state.customers[id]),
);

export const selectSelectedCustomer = createSelector(
  selectCustomersState,
  state => state.customers[state.selectedCustomerId],
);