nested-forms/apps/static-factory-methods/README.md

# Parent Component Creates Form; Child Components Define Structure

Another approach for refactoring a component into child sub-components where the parent component is responsible for creating the entre Reactive Form would be to define static factory methods within each child component rather than within a full-fledged service. As with the [Parent Component Creates Form and Passes Form Controls Into Child Components (Global Form)](../global-form/README.md) approach, the appropriate form controls would be passed into the children.

In many ways, this approach is a hybrid between the Parent Form and Global Form approaches.

```typescript
export class AppComponent implements OnInit, OnDestroy {
  contact: Contact;
  form: FormGroup;

  private subscription: Subscription;

  constructor(private service: ContactService, private fb: FormBuilder) {}

  public ngOnInit() {
    this.subscription = this.service
      .loadContact()
      .subscribe((data: Contact) => {
        this.contact = data;
        this.form = this.fb.group({
          name: NameComponent.buildForm(data.name),
          addresses: AddressListComponent.buildForm(data.addresses),
        });
      });
  }
}
```

The HTML templating will be identical to the Global Form approach.

## Static Form Builder Methods

Rather than having a separate factory service, this approach uses static methods on each of the child sub-classes. This approach intentionally couples the logic for creating a sub-form structure with the component that would display it, keeping the logic in one place rather than separating it between components and an otherwise unrelated service. The rule-of-thumb in this approach is that the component which needs to display the form to a user will best know what the structure of that form needs to be.

### Name Component

```typescript
  static buildForm(name: Name): FormGroup {
    return new FormGroup({
      firstName: new FormControl(name ? name.firstName : ''),
      lastName: new FormControl(name ? name.lastName : ''),
      middleName: new FormControl(name ? name.middleName : ''),
      prefix: new FormControl(name ? name.prefix : ''),
      suffix: new FormControl(name ? name.suffix : ''),
    });
  }
```

### Address List Component

```typescript
  static buildForm(addresses: Address[]): FormArray {
    const list: FormArray = new FormArray([]);

    if (addresses) {
      addresses.forEach(addr => {
        list.push(AddressComponent.buildForm(addr));
      });
    }

    return list;
  }
```

### Address Component

```typescript
  static buildForm(addr: Address): FormGroup {
    return new FormGroup({
      line1: new FormControl(addr ? addr.line1 : ''),
      line2: new FormControl(addr ? addr.line2 : ''),
      city: new FormControl(addr ? addr.city : ''),
      state: new FormControl(addr ? addr.state : ''),
      postalCode: new FormControl(addr ? addr.postalCode : ''),
    });
  }
```

## Pros

- The child components encapsulate the form controls and their display, while keeping the form creation logic separate from the actual template rendering
- The child components can easily be re-used

## Cons

- The overall shape of the form from the parent component's perspective is not always clear