Swedish SSN Regular expression reject users under a specific age

Question

I Have a problem with my regular expression. I have made it possible to valdiate correct swedish social security number to match these criteria.

• YYMMDDNNNN
• YYMMDD-NNNN
• YYYYMMDDNNNN
• YYYYMMDD-NNNN

But i would also like to reject a user to register if the user is under 18 years old. My reqular expression is looking like this at the moment: Do anyone encountered the same problem with the age range Swedish SSN?

  private const string RegExForValidation =
        @"^(\d{6}|\d{8})[-|(\s)]{0,1}\d{4}$";

UPDATE

 private const string RegExForValidation = @"^(?<date>\d{6}|\d{8})[-\s]?\d{4}$";
        string date = Regex.Match("19970918-1234", RegExForValidation).Groups["date"].Value;
        DateTime dt;

 [Required(ErrorMessage = "Du måste ange personnummer")]
        [RegularExpression(RegExForValidation, ErrorMessage = "Personnummer anges med 10 siffror (yymmddnnnn)")]
        public string PersonalIdentityNumber { get; set; }

Second Update

 public class ValidateOfAge : ValidationAttribute
{
    public bool IsOfAge(DateTime birthdate)
    {
        DateTime today = DateTime.Today;
        int age = today.Year - 18;
        if (birthdate.AddYears(birthdate.Year) < today.AddYears(-age))
            return false;
        else
            return true;
    }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        string RegExForValidation = @"^(?<date>\d{6}|\d{8})[-\s]?\d{4}$";
        string date = Regex.Match((string)value, RegExForValidation).Groups["date"].Value;
        DateTime dt;
        if (DateTime.TryParseExact(date, new[] { "yyMMdd", "yyyyMMdd" }, CultureInfo.InvariantCulture, DateTimeStyles.None, out dt))
            if (IsOfAge(dt))
                return ValidationResult.Success;
        return new ValidationResult("Personnummer anges med 10 siffror (yymmddnnnn)");
    }
}

Answer 1

You need to get the birthdate from the SSN, parse to DateTime, and then compare with today's date.

Here is the method checking if a person is of age:

public bool IsOfAge(DateTime birthdate)
{
    DateTime today = DateTime.Today;       // Calculating age...
    int age = today.Year - birthdate.Year;
    if (birthdate > today.AddYears(-age)) 
        age--;
    return age < 18 ? false : true;   // If the age is 18+ > true, else false.
}

And here is how you can use this:

string RegExForValidation = @"^(?<date>\d{6}|\d{8})[-\s]?\d{4}$";
string date = Regex.Match("19970918-1234", RegExForValidation).Groups["date"].Value;
DateTime dt;
if (DateTime.TryParseExact(date, new[] { "yyMMdd", "yyyyMMdd" }, new CultureInfo("sv-SE"), DateTimeStyles.None, out dt))
   Console.WriteLine(IsOfAge(dt));

Note that [-|(\s)] matches a -, |, (, whitespace or ). I am sure you only want to match a hyphen or whitespace.

I added a named capture to the regex and removed unnecessary symbols from the character class. Also, note that {0,1} is the same as ?.

UPDATE

To make it work in an MVC app, you need to implement a custom validator:

[Required(ErrorMessage = "Du måste ange personnummer")]
[ValidateOfAge]  // <---------------------------- HERE
public string PersonalIdentityNumber { get; set; }

And implement this as follows:

public class ValidateOfAge: ValidationAttribute
{
    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {                 
        string RegExForValidation = @"^(?<date>\d{6}|\d{8})[-\s]?\d{4}$";
        string date = Regex.Match((string)value, RegExForValidation).Groups["date"].Value;
        DateTime dt;
        if (DateTime.TryParseExact(date, new[] { "yyMMdd", "yyyyMMdd" }, new CultureInfo("sv-SE"), DateTimeStyles.None, out dt))
            if (IsOfAge(dt))
                return ValidationResult.Success;
        return new ValidationResult("Personnummer anges med 10 siffror (yymmddnnnn)");
    }
}