Angular ReactiveForm to Model Mapping

Question

I've been developing an app for a month now. I have come across many problems and almost all of them I've found solutions instead of opening threads but there is one design problem I still haven't figured out.

Suppose I have a small component called MonkeyComponent, it just has a form for my model (Monkey)

export class Car {
  model: string
}


export class Monkey {
  // If doc contains 8 digits
  driversLicense?: string;

  // If doc contains 13 digits
  pubId?: string;

  name: string;
  age: number;
  car: Car; // another model (could be added to form later)
}


export class AppComponent {
  formGroup: FormGroup;

  constructor(private fb: FormBuilder, private store: MonkeyStore) {
    this.formGroup = this.fb.group({
      name: [''],
      doc: [''],
      age: [''],
    });
  }

  save() {
    // now I need to map my form value to my monkey model
    // but they are mismatched (because doc can be used to populate
    // either pubId or driversLicense)
  }
}

This form mapping is common in many models of my project (one field of the form representing another field in the model)

Also I can't create multiple fields (client requirement)

How would you create this mapping? I am open to design suggestions (class model is not required if you have a better option)

Is there a Reactive-way to do this?

Is it avoidable to not have to use Object.assign and then manually mapping the divergent fields?

A clean solution would be to find a way to this.formGroup.value be

{
   pubId: '1234567890123',
   name: 'Miwalkey',
   age: 12,
}

or

{
   driversLicense: '12345678',
   name: 'Miwalkey',
   age: 12,
}

depending on the value (length) of doc.

Answer 1

I think this would be the designed approach:

ngOnInit() {
    this.formGroup.valueChanges.subscribe(val => {
         if (val.doc.length === 13) {
             monkey.pubId = val.doc;
         } else {
             monkey.driversLicense = val.doc;
         }
    });
}

or you could do

this.formGroup.get('doc').valueChanges.subscribe(val => {
       if (val.length === 13) {
         monkey.pubId = val;
       } else {
         monkey.driversLicense = val;
       }
  });

also if you're using ngModel you could put the same logic inside of an (ngModelChange) callback.

Answer 2

My current solution is this (I find this VERY ugly)

Base Form Model

export class FormModel {
  constructor(input?: any) {
    if (input) {
      this.fromJSON(input);
    }
  }

  fromJSON(input: any): this {
    return Object.assign(this, input);
  }
}

Car (model)

export class Car extends FormModel {
  model: string;
}

Monkey (model)

export class Monkey extends FormModel {
  pubId?: string;
  driversLicense?: string;

  car: Car;
  name: string;
  age: number;

  fromJSON(input: any): this {
    super.fromJSON(input);

    this.setDoc(input.doc);
    this.car = new Car(input.car);

    return this;
  }

  setDoc(doc: string) {
    if (doc.length === 8) {
      this.driversLicense = doc;
    } else if (doc.length === 13) {
      this.pubId = doc;
    }

    delete this['doc'];
  }
}

MonkeyComponent

export class MonkeyComponent {
  formGroup: FormGroup;

  constructor(private fb: FormBuilder, private store: MonkeyStore) {
    this.formGroup = this.fb.group({
      name: [''],
      doc: [''],
      age: [''],
    });
  }

  save() {
    const monkey = new Monkey(this.formGroup.value);
    console.log(monkey );
  }
}