at least one field is required in angular 4 forms

Question

I'm using angular 4 forms and I have some fields. and first_name, last_name and company are really important for me. I want to force the user to fill one of these 3 fields. how can I do it?

here are .ts codes:

this.contactForm = this.fb.group({
        first_name: [null, Validators.compose([Validators.required])],
        last_name: [null, Validators.compose([Validators.required])],
        email: [null, Validators.compose([this.validateEmail])],
        company: [null],
        position: [null],
      });

an html:

 <form [formGroup]="contactForm" fxLayout="column">
            <md-input-container class="data_light">
              <input class="data_font capital" mdInput placeholder="{{'Contacts.FirstName' | translate}}" [formControl]="contactForm.controls['first_name']">
            </md-input-container>
            <small *ngIf="contactForm.controls['first_name'].hasError('required') && contactForm.controls['first_name'].touched" class="mat-text-warn data_light">{{'Contacts.firstNameReq' | translate}}
            </small>
            <md-input-container class="data_light">
              <input class="data_font capital" mdInput placeholder="{{'Contacts.lastName' | translate}}" [formControl]="contactForm.controls['last_name']">
            </md-input-container>
            <small *ngIf="contactForm.controls['last_name'].hasError('required') && contactForm.controls['last_name'].touched" class="mat-text-warn data_light">{{'Contacts.lastNameReq' | translate}}
            </small>
            <md-input-container class="data_light">
              <input class="data_font" mdInput placeholder="{{'Contacts.email' | translate}}" [formControl]="contactForm.controls['email']"
                (blur)="checkContactEmail()">
            </md-input-container>
            <small *ngIf="contactForm.controls['email'].hasError('validateEmail') && contactForm.controls['email'].dirty" class="mat-text-warn data_light">{{'Contacts.emailValid' | translate}}
            </small>
            <small *ngIf="!emailValid" class="mat-text-warn data_light">{{emailMessage}}
            </small>
            <md-input-container class="data_light">
              <input class="data_font capital" mdInput placeholder="{{'Contacts.Company' | translate}}" [formControl]="contactForm.controls['company']">
            </md-input-container>
            <md-input-container class="data_light">
              <input class="data_font capital" mdInput placeholder="{{'Contacts.Position' | translate}}" [formControl]="contactForm.controls['position']">
            </md-input-container>
          </form>

Answer 1

private atLeastOneValidator = () => {
    return (controlGroup) => {
        let controls = controlGroup.controls;
        if ( controls ) {
            let theOne = Object.keys(controls).find(key=> controls[key].value!=='');
            if ( !theOne ) {
                return {
                    atLeastOneRequired : {
                        text : 'At least one should be selected'
                    }
                }
            }
        }
        return null;
    };
};

Above is a reusable validator and you can use it like this :

 this.contactForm.setValidators(this.atLeastOneValidator())

This makes the whole contactForm invalid if none of the fields have a value.

Note that the contactForm's default validation will still work nicely and you don't have to care about the number of fields in your form and everything is dynamically handled

EDIT :

Note that the atLeastOneValidator is checking for the values to not to be empty , but if you wanted to say :

At least one of them fields must be valid, then you can simply adjust the conditions to below

 let theOne = Object.keys(controls).find(key=> controls[key].valid );

You can then use the error in your template like this :

 <small *ngIf="contactForm.hasError('atLeastOneRequired')" class="mat-text-warn data_light">{{contactForm.getError('atLeastOneRequired')}}
        </small>

Answer 2

Disable your button until required fields are not fileld by user

<button type='submit' [disabled]='!contactForm.valid'> Submit</button>

Then call function to check disable like this

<button type='submit' [disabled]='checkValid()'> Submit</button>
checkValid() {
  if(this.contactForm.get('first_name').valid || this.contactForm.get('last_name').valid || this.contactForm.get('email').valid) {
    return false;
  } else {
    return true;
  }
}

Answer 3

I provide a better customized way for some fields only, and not for all fields of the form. Also,

• Not like this <button [disabled]="checkValid()">,

• But to use directly <button [disabled]="form.invalid || form.pristine || loading">

Fields can be provided via Array param as following:

export const atLeastOneHasValue = (fields: Array<string>) => {
    return (group: FormGroup) => {
        for (const fieldName of fields) {
            if (group.get(fieldName).value) {
                return null;
            }
        }
        return { paymentMethodRequired: true };
    };
};

// Form group
form = this.formBuilder.group({
   field1: [],
   field2: [],
   field3: [],
   field4: []
}, {
    validators: atLeastOneHasValue(['field2', 'field3'])
});

You then, can check and show error as following in the template, saving button will be disabled thanks to form.invalid boolean:

<mat-error *ngIf="form.hasError('paymentMethodRequired')">
    {{"ERROR_PAYMENT_METHOD_REQUIRED" | translate}}
</mat-error>