Binding a text input to a property in an observable object - Angular 2+

Question

I am building an app Using Angular 5 and I am trying to build a dynamic form. This form, which is like a bet slip or shopping cart, is a array of objects which comes from a service as an observable. I am having difficulty figuring out how to add an input field and bind it to a property in each bet object.

The observable betSlipItems array looks like this:

[
  {
    "Id": 1,
    "betslipTeamName": "La Rochelle",
    "stake": null
  },
  {
    "Id": 2,
    "betslipTeamName": "North Queensland Cowboys",
    "stake": null
  }
]

And what I want to do is create an input field and bind it to the 'stake' property of each bet object.

This is my code for bet-slip.component.ts so far:

import { FormBuilder, FormGroup, FormArray } from '@angular/forms';
import { Component, OnInit, Input } from '@angular/core';
import { Bets } from '../../../shared/models';
import { BetService } from '../../../shared/services/bet.service';
import { Observable } from 'rxjs';
import { of } from 'rxjs/observable/of';

@Component({
  selector: 'bet-slip',
  templateUrl: './bet-slip.component.html',
  styleUrls: ['./bet-slip.component.scss']
})

export class BetSlipComponent implements OnInit {

  public betSlipItems$: Observable<Bets[]> = of([]);
  public betSlipItems: Bets[] = [];
  public betsForm: FormGroup;

  constructor( private betService: BetService, private _fb: FormBuilder) {
    this.betSlipItems$ = this.betService.getBets();
  }

  ngOnInit() {

    this.betsForm = new FormGroup({
        stake: new FormControl()
    });

    this.betSlipItems$.subscribe((betSlipItems) => {
      this.betSlipItems = betSlipItems;
    });

  }
}

and my component bet-slip.component.html looks like this:

 <form [formGroup]="betsForm">
      <div *ngFor="let bet of betSlipItems; let i=index">
        {{bet.betslipTeamName }}
        <input type="text" formControlName="stake">
      </div>
 </form>

I know this is incorrect. How can I fix this?

here the formControlName is / should be dynamic right like a form arry or something ? — Rahul Singh
– Rahul Singh, Commented Jan 7, 2018 at 9:59
@Eliseo - thanks. I did try that but couldn't get it to work properly with the observable as I don't have very much experience with them. — Jose the hose
– Jose the hose, Commented Jan 7, 2018 at 10:08

halfer · Accepted Answer · 2019-11-01 22:33:11Z

The problem is that you must know what need and what expect. I suppose you want to make a form Array with "Id","betslipTeamName" and "stake" (as minimum you need Id and stake) not only stake. To work with a ReactiveForm with an array it's easy. In general we have a service that return our data. I put a full example, I expect this help you

//simple service that read a json (you have one yet -it's only to complete my example-)
@Injectable()
export class AppDataService {

  constructor(private httpClient:HttpClient) { }
  read(key:any)
  {
    return this.httpClient.get('../assets/data.json')
  }
}

Our component have a .html like this

<div *ngIf="yet">
<!--I put a *ngIf to avoid an error at first-->
  <form [formGroup]="dataForm" (ngSubmit)="submit(dataForm)" novalidate>
    <!--see that the "formArrayName" is "lista" 
    don't confuse with the *ngFor of "lista" (the lista in ngFor is a getter)
    -->
    <div formArrayName="lista" *ngFor="let lista of lista.controls;let i=index">
      <div [formGroupName]="i"> <!--it's necesary a formGroupName=i-->
      <!--we can use labels here -->
      {{labels[i].Id}}{{labels[i].Text}}
          <!--the input we need , some can be readOnly -->

          <input type="text" class="form-control" formControlName="Id">
          <input type="text" class="form-control" formControlName="betslipTeamName">
          <input type="text" class="form-control" formControlName="stake">
      </div>
      <hr>
    </div>
  </form>
   <!---this it's only to check the value of the form-->
  {{dataForm?.value |json}}
</div>

The component.ts it's like

@Component({
  selector: 'app-app-form',
  templateUrl: './app-form.component.html',
  styleUrls: ['./app-form.component.css']
})
export class AppFormComponent implements OnInit {

  dataForm: null | undefined | FormGroup;  //we have a dataForm
  data: any;  //normally we have a data too. It's not necesary that the data was identical to dataFrom 
  labels:any[] //we create an array [{Id,Text}]
  yet:boolean=false;  //I use this variable when all it's ready

  get lista() {  //<--This is the gettet that we use in the *ngFor
    return (this.dataForm) ? this.dataForm.get('lista') : null;
  };

  constructor(private fb: FormBuilder, private dataService: AppDataService) { }

  ngOnInit() {
    let key: any;
    this.dataService.read(key).subscribe(
      (response:any[]) => {
    if (response) {
      this.data = response; //this.data is an array[{"Id": 1,..}.{"Id":2..}]
      //You can create a label array with Id,Text
      this.labels=response.map((item:any)=>{return {Id:item.Id,Text:item.betslipTeamName}})
      this.dataForm = this.createFormGroup(this.data);// dataForms is an object {lista:[{..},{..}]}
      this.yet=true;
    }
  });
  }
  submit(dataForm:any)
  {
    if (dataForm.valid)
    {
      console.log(dataForm.value);
    }
  }
  createFormGroup(data: any) {
    let lista = this.buildArray(data);  //create an array of Controls

    let dataForm = this.fb.group({
      lista: lista
    });
    //see that dataForms is an object {lista:[{..},{..}]}
    return dataForm;
  }

  buildArray(myArray: any[]) {
    //witch each data, we create a fbGroup 
    const arr = myArray.map(data => {
      return this.fb.group({
        "Id": [data.Id], //we can omit some control
        "betslipTeamName": [data.betslipTeamName],
        "stake": [data.stake],
      });
    });
    //And return a array of fbGroup
    return this.fb.array(arr);
  }
}

Many thanks for your answer. I just added this code and it worked! Thank you!!

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