Angular Reactive Forms: advanced patterns with Async Validators on Conditional Fields
I'm reviewing some code and I'm testing a new approach and I'm sure I'm missing something obvious here, but I've looked through the documentation and I'm still confused about I'm working with Angular 14 and using Reactive Forms to create a dynamic form where certain fields become required based on the selection of a dropdown... However, I'm working with an scenario where the async validator I applied to one of the fields isn't being triggered correctly when the field's condition changes. The form is structured so that when a user selects 'Yes' from a dropdown, a text input for additional details appears. I have an async validator that checks if the input is unique in the database. The question arises when I switch back to 'No' and then select 'Yes' again; the validator doesn't seem to run, and the field remains invalid without showing the validation message. Here’s a snippet of my form initialization: ```typescript this.myForm = this.fb.group({ userChoice: ['No'], additionalDetails: ['', { asyncValidators: [this.uniqueValidator.bind(this)] }] }); ``` I have a method that triggers when the user selects an option in the dropdown: ```typescript onUserChoiceChange(event: Event) { const value = (event.target as HTMLSelectElement).value; const additionalDetailsControl = this.myForm.get('additionalDetails'); if (value === 'Yes') { additionalDetailsControl?.setValidators([Validators.required, this.uniqueValidator.bind(this)]); } else { additionalDetailsControl?.clearValidators(); } additionalDetailsControl?.updateValueAndValidity(); } ``` I've confirmed that when 'No' is selected, the validators are properly cleared, but when I switch back to 'Yes', the async validator doesn't get invoked again, which leads to the form being exploring in an invalid state without any behavior messages displayed. I've also tried using `updateValueAndValidity({ emitEvent: true })` but still face the same scenario. The async validator itself is working correctly when triggered in isolation. Here is the async validator function: ```typescript uniqueValidator(control: AbstractControl): Observable<ValidationErrors | null> { return this.userService.checkIfUnique(control.value).pipe( map(isUnique => (isUnique ? null : { notUnique: true })), catchError(() => of(null)) ); } ``` Does anyone have insights into why the async validator isn't triggering when the field becomes visible again? I'm looking for any best practices or common pitfalls to avoid in this scenario. My development environment is Windows. I'm working in a Windows 10 environment. Any ideas how to fix this? The stack includes Typescript and several other technologies. I'd really appreciate any guidance on this.