Write Custom Validation for Multiple Fields using MVC - asp.net-mvc

Question

I have a customer form having phone number fields like CountryCode, AreaCode and PhoneNumber. I would like to write a custom validation for these 3 fields where all of them can either remain empty (they are optional) or all of them can remain filled (no field can be left empty if one or two are filled).
Am trying to write a custom validation for this situation, however, am not clear how to do it. Please help.

Answer 1

It's unclear exactly what you're looking for here. If you're just struggling with the boolean logic, all you need is:
if (!String.IsNullOrWhiteSpace(model.CountryCode) ||
!String.IsNullOrWhiteSpace(model.AreaCode) ||
!String.IsNullOrWhiteSpace(model.PhoneNumber))
{
if (String.IsNullOrWhiteSpace(model.CountryCode)
{
ModelState.AddModelError(nameof(model.CountryCode), "Country code is required.");
}
if (String.IsNullOrWhiteSpace(model.AreaCode)
{
ModelState.AddModelError(nameof(model.AreaCode), "Area code is required.");
}
if (String.IsNullOrWhiteSpace(model.PhoneNumber)
{
ModelState.AddModelError(nameof(model.PhoneNumber), "Phone number is required.");
}
}
Essentially, you just first check to see if any of them have a value. Then, you individually add an error for each one that does not have a value.
That said, these broken out phone number fields are atrocious. I'm not sure where the idea came from, but it's like you just can't get people off of them now. Phone number formats vary wildly, and not every phone number actually has an "area code". It's far better to have a single "phone" field where the user can simply type their entire phone number. Then, you can use something like this port of Google's libphonenumber library to validate the number and format it into a standard form. You can even use the library to parse out the individual pieces of country code, area code, and number, if you need to store it like this. Just be prepared that the area code may not have a value and even if it does, it may not be exactly 3 digits. Same goes for number portion, as well: you can't assume it will always be 7.
Validate a phone number
var phoneUtil = PhoneNumberUtil.GetInstance();
try {
var phoneNumber = phoneUtil.Parse(model.Phone, countryISO2);
if (!phoneUtil.IsValidNumber(phoneNumber))
{
ModelState.AddModelError(nameof(model.Phone), "Invalid phone number.");
}
} catch (NumberParseException) {
ModelState.AddModelError(nameof(model.Phone), "Invalid phone number.");
}
Where countryISO2 is the two character country code: "US", "GB", etc. If you want to accept international phone numbers, you should collect the country from the user.
Format a phone number
phoneUtil.Format(phoneNumber, PhoneNumberFormat.NATIONAL);
Get component parts of a phone number
var countryCode = phoneNumber.CountryCode;
string areaCode;
string number;
var nationalSignificantNumber = phoneUtil.GetNationalSignificantNumber(phoneNumber);
var areaCodeLength = phoneUtil.GetLengthOfGeographicalAreaCode(phoneNumber);
if (areaCodeLength > 0) {
areaCode = nationalSignificantNumber.Substring(0, areaCodeLength);
number = nationalSignificantNumber.Substring(areaCodeLength);
} else {
areaCode = "";
number = nationalSignificantNumber;
}