How to get checked values into an array for Angular Template Driven Form (ngModel)

Question

I'm attempting to use template driven forms, binding to a model in the html to a new instance of lets say Person. I've been unsuccessful in creating a proper binding for checkboxes to a single array property on my model.

The idea is data will come from an api or other source, dynamically render checkboxes via *ngFor and bind what is selected to the Person models property which would be an array of numbers. For example:

class Person {
  firstName: string;
  someCheckboxPropList: number[];
}

and data could be anything really

const dynamicData = [
  { name: 'name1', value: 1 },
  { name: 'name2', value: 2 }
];

my expected output would be something along the lines of [ 1, 2 ] if both values where to be checked and if only the second was checked [ 2 ].

Here's a sample of what the PersonComponent.ts file might look like

@Component({ ... })
export class PersonComponent {

    submitted = false;

    model = new Person();

    constructor() { }

    onSubmit(form) {
        this.submitted = true;
        console.log(form);
    }

}

And where I'm at with the components html file.

<form (ngSubmit)="onSubmit(form)" #form="ngForm">

    <input type="text" [(ngModel)] name="person.firstName">

    <div *ngFor="let dataItem of dynamicData" >
        <input 
            type="checkbox"
            ngModel
            name="dynamicData"
            [value]="dataItem.value">
        <label>{{dataItem.name}}</label>
    </div>

</form>

This does not work (and is sample code anyway).

Answer 1

the idea is have two things: Person and PersonForm, so,e.g

person={firstName:"Jessy",props:[1,2]
//but 
personForm={firstName:"Jessy",props:[true,true]

So, make two functions

  createForm(person) {
    return {
      firstName: person.firstName,
      props: this.dynamicData.map(x => person.props.indexOf(x.value) >= 0)
    }
  }
  retrieveData(personForm) {
    let props: number[] = [];
    personForm.props.forEach((v, index) => {
      if (v)
        props.push(this.dynamicData[index].value)
    }
    )
    return {
      firstName: personForm.firstName,
      props: props
    }
  }

Well, we have already all we need. When we received a person, create a personForm that it's the data we change in the form. In submit simply call to retrieveData to get the value of person.

When we have a person create a personForm,e.g.

this.service.getPerson().subscribe(person=>
    {
       this.personForm=createForm(person)
    }
)

Our form

<form *ngIf="personForm" (submit)="sendData(personForm)">
  <input name="firtName" [(ngModel)]="personForm.firstName">
  <div *ngFor="let item of dynamicData;let i=index">
  <input name="{{'prop'+i}}" 
         type="checkBox" [(ngModel)]="personForm.props[i]">{{item.name}}
  </div>
  <button>Submit</button>
</form>
{{personForm|json}}<br/>
{{retrieveData(personForm)|json}}

And our sendData function

sendData(personForm)
{
    console.log(this.retrieveData(personForm))
}

I make a simple stackblitz

Update

NOTE:We can use the spred operator to asing properties, so

  createForm(person) {
    return {
      ...person, //All the properties of person, but
      props: this.dynamicData.map(x => person.props.indexOf(x.value) >= 0)
    }
  }
  retrieveData(personForm) {
    let props: number[] = [];
    personForm.props.forEach((v, index) => {
      if (v)
        props.push(this.dynamicData[index].value)
    }
    )
    return {
      ..personForm, //all the properties of personForm, but
      props: props
    }
  }

NOTE2: In a "real world" the persons goes from a service. Consider the idea that service get/received the "personForm" and put the functions to transform in the service

//in service
getPerson()
{
    return this.httpClient.get("...").map(res=>this.createForm(res))
}
savePerson(personForm)
{
    return this.httpClient.post("...",this.retrieveData(personForm))
}