Create a custom validator to validate against multiple form fields

Question

I have the following form setup:

this.form = new FormGroup({
  ...
  year: new FormControl("", validateDateMethod(year, month, day)),
  month: new FormControl("", validateDateMethod(year, month, day)),
  day: new FormControl("", validateDateMethod(year, month, day))
});

I want to create a custom validator to validate the date based on the 3 fields.

Is it possible to create a validator based on multiple form values?

Normal customs validators just take in the current control and any parameter values.

Thanks

Please look into code in this link: https://stackoverflow.com/a/44449802/3875919 — user3875919, Nov 12 '19 at 09:34
I've tried something similar to that but I receive an error: Argument of type is not assignable to parameter of type 'ValidatorFn | ValidatorFn[] | AbstractControlOptions'. Object literal may only specify known properties, and 'validator' does not exist in type 'ValidatorFn | ValidatorFn[] | AbstractControlOptions — Sun, Nov 12 '19 at 09:45
You could achieve by setting the custom property in the errors object of the `FormControl` and then display the error message in the DOM using `*ngIf` directive. — user3875919, Nov 12 '19 at 10:17

score 1 · Accepted Answer · edited Nov 12 '19 at 09:57

1

You can group all the three dates to a formgroup and add validator to it. Then you can validate across all the three fields.

 this.form = new FormGroup({
      ...
      dateGroup:this.formBuilder.group({
      year: new FormControl(""),
      month: new FormControl(""),
      day: new FormControl("")
    },{validator:validateDates}) 
  });

    validateDates(c:AbstractControl){
    const year = c.get('year');
    const month = c.get('month');
    const day = c.get('day');
    ....
    }

edited Nov 12 '19 at 09:57

user3875919

303
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answered Nov 12 '19 at 09:45

Saloo

816
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you need to pass the whole formGroup as argument to access to all controls :validateDates(c:FormGroup) – Bilel-Zheni Nov 12 '19 at 10:20
It wont create problem because FormGroup extends AbstractControl – Saloo Nov 12 '19 at 10:45
Perfect. Thanks. – Sun Nov 12 '19 at 11:11

Create a custom validator to validate against multiple form fields

1 Answers1