Issue

I’m trying to build an inline editable table using the latest material+cdk for angular.

Question

How can I make mat-table use [formGroupName] so that the form fields can be referenced by its correct form path?

This is what I got so far: Complete StackBlitz example

Template

<form [formGroup]="form">
  <h1>Works</h1>
  <div formArrayName="dates" *ngFor="let date of rows.controls; let i = index;">
    <div [formGroupName]="i">
      <input type="date" formControlName="from" placeholder="From date">
      <input type="date" formControlName="to" placeholder="To date">
    </div>
  </div>


  <h1>Wont work</h1>
  <table mat-table [dataSource]="dataSource" formArrayName="dates">
    <!-- Row definitions -->
    <tr mat-header-row *matHeaderRowDef="displayColumns"></tr>
    <tr mat-row *matRowDef="let row; let i = index; columns: displayColumns;" [formGroupName]="i"></tr>

    <!-- Column definitions -->
    <ng-container matColumnDef="from">
      <th mat-header-cell *matHeaderCellDef> From </th>
      <td mat-cell *matCellDef="let row"> 
        <input type="date" formControlName="from" placeholder="From date">
      </td>
    </ng-container>

    <ng-container matColumnDef="to">
      <th mat-header-cell *matHeaderCellDef> To </th>
      <td mat-cell *matCellDef="let row">
        <input type="date" formControlName="to" placeholder="To date">
      </td>
    </ng-container>
  </table>
  <button type="button" (click)="addRow()">Add row</button>
</form>

Component

export class AppComponent implements  OnInit  {
  data: TableData[] = [ { from: new Date(), to: new Date() } ];
  dataSource = new BehaviorSubject<AbstractControl[]>([]);
  displayColumns = ['from', 'to'];
  rows: FormArray = this.fb.array([]);
  form: FormGroup = this.fb.group({ 'dates': this.rows });

  constructor(private fb: FormBuilder) { }

  ngOnInit() {
    this.data.forEach((d: TableData) => this.addRow(d, false));
    this.updateView();
  }

  emptyTable() {
    while (this.rows.length !== 0) {
      this.rows.removeAt(0);
    }
  }

  addRow(d?: TableData, noUpdate?: boolean) {
    const row = this.fb.group({
      'from'   : [d && d.from ? d.from : null, []],
      'to'     : [d && d.to   ? d.to   : null, []]
    });
    this.rows.push(row);
    if (!noUpdate) { this.updateView(); }
  }

  updateView() {
    this.dataSource.next(this.rows.controls);
  }
}

Problem

This wont work. Console yields

ERROR Error: Cannot find control with path: ‘dates -> from’

It seems as if the [formGroupName]="i" has no effect, cause the path should be dates -> 0 -> from when using a formArray.

My current workaround: For this problem, I’ve bypassed the internal path lookup (formControlName="from") and use the form control directly: [formControl]="row.get('from')", but I would like to know how I can (or at least why I cannot) use the Reactive Form preferred way.

Any tips are welcome. Thank you.

---

Since I think this is a bug, I’ve registered an issue with the angular/material2 github repo.

Solution

I would use the index which we can get within matCellDef binding:

*matCellDef="let row; let index = index" [formGroupName]="index"

Forked Stackblitz

For solving problems with sorting and filtering take a look at this answer Angular Material Table Sorting with reactive formarray