Angular dynamic form nested fields

Implementing dynamic form with formArray.

Well, the things are more complex. I make a stackblik, see demo

I'll try to explain how extends the https://angular.io/guide/dynamic-form to allow Form Array.

The first we need make is create a new type of question, a questionArray

import { QuestionBase } from './question-base';

export class ArrayQuestion extends QuestionBase<string> {
  controlType = 'array';
  type: any;

  constructor(options: {} = {}) {
    super(options);
  }
}

We must change question base to add a new property "children"

export class QuestionBase<T> {
  value: T;
  ...
  children:any[];

  constructor(options: {
      value?: T,
      ...
      children?:any
    } = {}) {
    this.value = options.value;
    ...
    this.children=options.children || null;
  }
}

Add change the question-control service to allow manage formArrays

toFormGroup(questions: QuestionBase<any>[]) {
    let group: any = {};

    questions.forEach(question => {
      //If the control type is "array" we create a FormArray
      if (question.controlType=="array") {
         group[question.key]=new FormArray([]);
      }
      else {
        group[question.key] = question.required ? new FormControl(question.value || '', Validators.required)
          : new FormControl(question.value || '');
      }
    });
    return new FormGroup(group);
  }

Well We transform the dynamic-form.component to show a FormArray

<div *ngFor="let question of questions" class="form-row">
    <ng-container *ngIf="question.children">
        <div [formArrayName]="question.key">
            <div *ngFor="let item of form.get(question.key).controls; let i=index" [formGroupName]="i">
                <div *ngFor="let item of question.children">
                    <app-question [question]="item" [form]="form.get(question.key).at(i)"></app-question>
                </div>
            </div>
        </div>
    </ng-container>
    <ng-container *ngIf="!question.children">
        <app-question [question]="question" [form]="form"></app-question>

    </ng-container>
</div>

And just it doit. Well, how increment and decrement the formArrays? We have two buttons

  <button (click)="addControls('myArray')"> Add </button>
  <button (click)="removeControls('myArray')"> Remove </button> <br><br>

And two functions addControls and removeControls

  addControls(control: string) {
    let question: any = this.questions.find(q => q.key == control);
    let children = question ? question.children : null;
    if (children)
      (this.form.get(control) as FormArray).push(this.qcs.toFormGroup(children))
  }
  removeControls(control: string){
    let array=this.form.get(control) as FormArray;
    array.removeAt(array.length-1);
  }

Update I forgot add and example of questions:

let questions: QuestionBase<any>[] = [

      new TextboxQuestion({
        key: 'firstName',
        label: 'First name',
        value: '',
        required: true,
        order: 1
      }),

      new TextboxQuestion({
        key: 'lastName',
        label: 'Last name',
        value: '',
        required: true,
        order: 2
      }),
      new ArrayQuestion({
        key: 'myArray',
        value: '',
        order: 3,
        children: [
          new TextboxQuestion({
            key: 'emailAddress',
            label: 'Email',
            type: 'email',
            order: 3
          }),
          new DropdownQuestion({
            key: 'brave',
            label: 'Bravery Rating',
            options: [
              { key: 'solid', value: 'Solid' },
              { key: 'great', value: 'Great' },
              { key: 'good', value: 'Good' },
              { key: 'unproven', value: 'Unproven' }
            ],
            order: 4
          })
        ]
      })
    ];