The Power of Angular 2's Reactive Form Validation

I am currently developing a custom validator for a group of inputs within my dynamic form.

this.transitionForm = this.fb.group({
  effectiveStartDate: [this.utils.dateToISO(startDate), Validators.compose([Validators.required, this.validateDates])],
  effectiveEndDate: [(endDate ? endDate : ''), Validators.compose([Validators.required, this.validateDates])],
});

/**
 * Ensures that the selected start and end dates are valid.
 *
 * @param formGroup
 */
validateDates(formgroup: FormGroup) {

    const start = formgroup.controls["effectiveStartDate"].value;
    const end = formgroup.controls["effectiveEndDate"].value;

    /**
     *   Validation Rules
     * - End date should not be before the start date
     * - Start date should not be after the end date
     * - Start date should not be empty
     * - End Date should not be empty
     */
    if ((end < start) || (start > end) || !start || !end) {
        return { invalidDates: true };
    } else {
        return null;
    }
}

HTML:

<div *ngIf="!transitionForm.controls['effectiveEndDate'].valid">
 <p *ngIf="transitionForm.controls['effectiveEndDate'].errors.invalidDates">
  Invalid End Dates
 </p>
</div>

When I leave the end date field empty, the error message is not displaying. I suspect that I might be invoking the validator incorrectly. I used the `compose` method to combine multiple validators, but I am unsure if I need to pass any parameters with it.

Update:

Below is the complete current form code without the individual control validators. It also demonstrates that there is already a form-level validator set up, possibly incorrectly.

How can I incorporate multiple validators?

this.transitionForm = this.fb.group({
    changeType: ['', Validators.required],
    effectiveStartDate: [this.utils.dateToISO(startDate), Validators.required],
    effectiveEndDate: [(endDate ? endDate : ''), Validators.required],

},
    {
        // Ensure at least one transition field is selected
        validator: (formGroup: FormGroup) => {
            return this.validateFilter(formGroup);
        }
    });

Answer №1

I completely agree with Deborah's suggestion of utilizing a nested formgroup for handling your dates. This approach is not only more efficient in terms of performance, especially when dealing with a large number of fields in your form, but also ensures that validation is triggered only when changes occur within the specific 'dates' group, as demonstrated by Deborah:

...
dates: this.fb.group({
  effectiveStartDate: [this.utils.dateToISO(startDate), Validators.required],
  effectiveEndDate: [(endDate ? endDate : ''), Validators.required],
},{validator: this.validateDates})
...

In terms of your custom validator, there is no need to check for the presence of dates since you have already utilized Validators.required. You can simplify your custom validator as follows:

validateDates(dates: FormGroup) { // refering to the 'dates' formgroup
  const start = dates.controls["effectiveStartDate"].value;
  const end = dates.controls["effectiveEndDate"].value;

  if ((end < start) || (start > end)) {
     return { invalidDates: true };
  } else {
     return null;
  }
}

Regarding the issue of displaying error messages in the template, using errors.invalidDates will not work. Instead, you can make use of hasError to handle this gracefully:

<p *ngIf="transitionForm.hasError('invalidDates', 'dates')">

Answer №2

When creating a validator for a group of controls, make sure to assign the validator to the entire group and not individual controls.

    this.userForm = this.fb.group({
        username: ['', [Validators.required, Validators.minLength(3)]],
        password: ['', [Validators.required, Validators.maxLength(50)]],
        securityQuestions: this.fb.group({
            question: ['', [Validators.required, Validators.pattern('[a-zA-Z ]*')]],
            answer: ['', Validators.required],
        }, {validator: securityQuestionMatcher}),
        phone: '',
        notifications: 'email',
        age: ['', ageRange(18, 100)],
        subscribeNewsletter: true,
        addresses: this.fb.array([this.createAddress()])
    });

In addition, you can remove the compose function as it is no longer necessary in the current version of Angular.

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