Selecting a "null" value using mat-option with Angular 7 Reactive Forms Not Working

Question

I am trying to default select an option which contains a "null" [value] in a mat-select. The problem is, it does not select the option with the "null" [value] when the html is displayed. I am using Angular 7 Reactive Forms with Angular Material 7. Here is what I have -

Html:

<mat-select placeholder="User" formControlName="userId">
  <mat-option [value]="null">None</mat-option>
  <mat-option *ngFor="let user of users" [value]="user.userId">
      {{ user.name }}
  </mat-option>
</mat-select>

Component.ts:

this.userId.setValue(null);

The line above assumes that I have already instantiated my formGroup with one of the formControls being called "userId" and "this.userId" is a property of my component which references "this.userForm.get('userId')".

So when I set the formControl value of "userId" to null nothing is ever selected in the html. I was under the impression that you can have a "null" value as one of the options of a mat-select, Am I wrong? If not, any suggestions on what I can do to get this to work the way I want.

Thanks!

Solution 1

You can not set the null because you have integer property (user.userId), The sample code should be work.

Template Code:

<form [formGroup]="patientCategory">
    <mat-form-field class="full-width">
        <mat-select placeholder="Category" formControlName="patientCategory">
            <mat-option [value]="0">None</mat-option>
            <mat-option *ngFor="let category of patientCategories" [value]="category.id">
                {{category.name}} - {{category.description}}
            </mat-option>
        </mat-select>
    </mat-form-field>

    <p>{{patientCategory.get('patientCategory').value | json}}</p>
</form>

Componet Code

import { Component, ViewChild } from '@angular/core';
import { FormBuilder, FormGroup, FormControl, Validators } from '@angular/forms';

/**
 * @title Basic table
 */
@Component({
  selector: 'table-basic-example',
  styleUrls: ['table-basic-example.css'],
  templateUrl: 'table-basic-example.html',
})
export class TableBasicExample {
  patientCategory: FormGroup;

  patientCategories = [{
    id: 1,
    name: 'name 1',
    description: 'description 1'
  }, {
    id: 2,
    name: 'name 2',
    description: 'description 2'
  }, {
    id: 3,
    name: 'name 3',
    description: 'description 3'
  }]

  constructor(private fb: FormBuilder) { }

  ngOnInit() {

    this.patientCategory = this.fb.group({
      patientCategory: [null, Validators.required]
    });

    //const toSelect = this.patientCategories.find(c => c.id == 3);
    this.patientCategory.get('patientCategory').setValue(0);
  }
}

Demo

Solution 2

Can you try pushing the default null values as first option of 'users' array.

this.users.unshift({
  userId: null,
  name: 'select'
});

Template:

<mat-select placeholder="User" formControlName="userId">
  <mat-option *ngFor="let user of users" [value]="user.userId">
      {{ user.name }}
  </mat-option>
</mat-select>