Conditional validation in Angular 2

Question

Validation in Angular 2 is pretty straight forward which is awesome. However, how would one go about making a required field optional if some other field is selected.

Here are my rules

this.contractsFilter = this.fb.group({
  selectedContractType: ['', [Validators.required]],
  selectedYear: ['', [Validators.required]],
  selectedPde: ['', [Validators.required]],
  refNo: ['', []]
});

I want other fields flagged as required to be 'un-required' if the refNo is provided by the user.

Answer 1

Here is how you can dynamically add or remove validator to some control

private addValidator(control, validator) {
    let existingValidators = control.validator;
    control.setValidators(Validators.compose([existingValidators, validator]));
    control.updateValueAndValidity();
  }

And to Remove validator

  private removeRequiredValidator(control, otherValidators) {
    control.clearValidators();
    if (otherValidators) {
      control.setValidators(otherValidators);
    }
    control.updateValueAndValidity();
  }

Answer 2

Both the use of custom validators and setValidators can get very complex very quickly. I prefer to configure the validators as they may be required and then conditionally enable or disable them.

Using exactly your code:

this.contractsFilter = this.fb.group({
  selectedContractType: ['', [Validators.required]],
  selectedYear: ['', [Validators.required]],
  selectedPde: ['', [Validators.required]],
  refNo: ['', []]
});

I would then subscribe to valueChanges for refNo:

this.contractsFilter.controls['refNo'].valueChanges.subscribe(value => {
  if (value) { // There is a refNo specified
    this.contractsFilter.controls['selectedContractType'].disable();
    this.contractsFilter.controls['selectedYear'].disable();
    this.contractsFilter.controls['selectedPde'].disable();
  } else {
    this.contractsFilter.controls['selectedContractType'].enable();
    this.contractsFilter.controls['selectedYear'].enable();
    this.contractsFilter.controls['selectedPde'].enable();
  }
});

Now your validators are all specified in one consistent place, and you can still control whether the validators are executed or not.