Set value of <mat-select> programmatically

Question

I'm trying to set value of 2 fields <input matInput> abnd <mat-select> programatically. For text input everything works as expected however for the <mat-select> on the view this field is just like it would have value off null. But if I would call console.log(productForm.controls['category'].value it prints correct value that I set programmatically. Am I missing something?

Here is the code:

form config:

productForm = new FormGroup({
    name: new FormControl('', [
        Validators.required
    ]),
    category: new FormControl('', [
        Validators.required
    ]),
});

setting value:

ngOnInit() {
    this.productForm.controls['name'].setValue(this.product.name);
        this.productForm.controls['category'].setValue(this.product.category);
    }
}

html:

<mat-form-field>
    <mat-select [formControlName]="'category'"
                [errorStateMatcher]="errorStateMatcher">
        <mat-option *ngFor="let category of categories" [value]="category">
            {{category.name}}
        </mat-option>
    </mat-select>
</mat-form-field>

Solution 1

Solved this issue with changing the value of <mat-option> from category object to its id.

<mat-form-field>
<mat-select [formControlName]="'category'"
        [errorStateMatcher]="errorStateMatcher">
<mat-option *ngFor="let category of categories" [value]="category.id">
    {{category.name}}
</mat-option>
</mat-select>
</mat-form-field>

and setting value:

this.productForm.controls['category'].setValue(this.product.category.id);

Solution 2

The Angular mat-select compares by reference between that object and all the available objects in the mat-select. As a result, it fails to select the items you have set in the category field. Consequently, you have to implement the compare function to compare any of the list items' attributes as you want, and then pass this function to the [compareWith] attribute of the mat-select.
To conclude, Here is a snapshot for the final markup and script:

<mat-form-field>
    <mat-select [formControlName]="category" [compareWith]="compareCategoryObjects">
        <mat-option *ngFor="let category of categories" [value]="category">
            {{category.name}}
        </mat-option>
    </mat-select>
</mat-form-field>

And in the component class:

compareCategoryObjects(object1: any, object2: any) {
    return object1 && object2 && object1.id == object2.id;
}

Now it will select the item -or items if multiple select- you set for the field.

Reference:
https://github.com/angular/material2/issues/10214

Working Sample:
https://stackblitz.com/edit/angular-material2-issue-t8rp7j

Solution 3

The way you can achieve this using objects is to change the markup like so:

<mat-select [formControlName]="'category'"
        [errorStateMatcher]="errorStateMatcher" [compareWith]="compareFn">
<mat-option *ngFor="let category of categories" [value]="category">
    {{category.name}}
</mat-option>
</mat-select>

Then in component

compareFn(x: Category, y: Category): boolean {
return x && y ? x.id === y.id : x === y;
}

Solution 4

I think in here you should use FormGroup.setValue.

According to your code,

this.productForm.setValue({
name: this.product.name,
category: this.product.category
});

For more info please refer the documentation

View more solutions

Comments

[Thomas Carlisle]

This is the actual right answer. The accepted answer, by the OP, worked because OP changed the object binding to the mat-select to be the Id field, which is of a type that is a primitive type in Angular. Hence the "compareWith" works as built into Angular. If one needs to bind the mat-select to an object, then the compareWith needs to be defined. Not unlike in Java you need to implement equals and hashcode if you expect things to really work right.

[C Alonso C Ortega]

this works well for me using reactive forms 😁