在multiLevel对象中使用ngFor的ngModel

Question

如何在多级对象的多ngModel循环中使用ngFor？

<div no-padding *ngFor="let addon of item.addons_list; let mainIndex= index">
  <div *ngIf="addon.has_sub">
    <ion-row *ngFor="let sub of addon.sub_list ; let sub1 = index">
      <ion-col col-12 no-padding>
        <ion-select dir="rtl" placeholder="{{ sub.name }}" [(ngModel)]="add[mainIndex][sub1]">
          <ion-option value="{{ch.id}}" *ngFor='let ch of sub.items'> {{ch.name}} </ion-option>
        </ion-select>
      </ion-col>
    </ion-row>
  </div>
</div>