Reactive Form - Formgroup with a nested formgroup throw exception on reset call with null values

[szanellato93]

[ ] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[X] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question

Current behavior

When i call form reset on a formGroup with nested formGroup passing it with a null value i receive a error "Cannot read property ... of null"

Expected behavior

Expected result is that on form reset with a null value the nested form group properties become all null.

Minimal reproduction of the problem with instructions

When i have a formGroup with a nested formGroup like this:

let form = this.fb.group({
Id: [null],
Nested: fb.group({
    Id: [null]
})
})

If i call a form reset or a patch value with a object like this:

form.reset({
Id: 1,
Nested: null
})

i receive the error "Cannot read property 'Id' of null" because he try to read the nested property from a null object

Expected result is that on form reset with a null value the nested form group properties become all null. This behavior happen when i call the reset without the nested properties:
form.reset({Id: 3})

What is the motivation / use case for changing the behavior?

Usually service return models with all properties and nested entities null if they don't exist instead return the nested entities initialized

[artem-galas]

I would like to take this issue.
But I'm not sure how to implement it.

The error occurred on .reset method for FormGroup. https://github.com/angular/angular/blob/master/packages/forms/src/model.ts#L1478

We can check if (control instanceof FormGroup) into this method, but I'm not sure if am I right.

Here is my idea:
As I understand we have to iterate through all controls from nested formGroup and reset value to null.
So basically we can call control._forEachChild.

Could you please advise me a little here?

Thanks.

[timrasche]

Any update on this?

[w5l]

This still happens, currently caused by the reset code in FormGroup here, specifically on line 1679:

angular/packages/forms/src/model.ts

Lines 1677 to 1684 in bd34bc9

	reset(value: any = {}, options: {onlySelf?: boolean, emitEvent?: boolean} = {}): void {
	this._forEachChild((control: AbstractControl, name: string) => {
	control.reset(value[name], {onlySelf: true, emitEvent: options.emitEvent});
	});
	this._updatePristine(options);
	this._updateTouched(options);
	this.updateValueAndValidity(options);
	}

It blindly assumes value is set to a non null value.

As a workaround, we're using the following reset code. Note that this modifies the input object which might be undesired, but in our use case it doesn't matter. YMMV.

export const resetForm = (group: FormGroup, value?: any, options?: {
    onlySelf?: boolean;
    emitEvent?: boolean;
}) => {
    const ensureValues = (g: FormGroup, v: any) => Object.keys(g.controls).forEach(key => {
        // The list of controls can change (for ex. controls might be removed) while the loop
        // is running (as a result of invoking Forms API in `valueChanges` subscription), so we
        // have to null check before invoking the callback.
        const control = g.controls[key];
        if (control instanceof FormGroup) {
            // Ensure the value to be bound to this formgroup is not null.
            v[key] = v[key] || {};
            // Recursively check child controls for nested formgroups.
            ensureValues(control, v[key]);
        }
    });
    ensureValues(group, value || {});
    group.reset(value, options);
};

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[dylhunn]

We'll need to see how breaking this fix is. I really hope it's not too breaking in g3 -- that would mean people are relying on app crashes 🤦

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