Datetime required (+18 years)

Question

I have a little problem, here is my code:

public partial class Tourist
    {

        public Tourist()
        {
            Reserve = new HashSet<Reserve>();
        }
        public int touristID { get; set; }

        [Required]
        [StringLength(50)]
        public string touristNAME { get; set; }

        public DateTime touristBIRTHDAY { get; set; }

        [Required]
        [StringLength(50)]
        public string touristEMAIL { get; set; }

        public int touristPHONE { get; set; }

        public virtual ICollection<Reserve> Reserve { get; set; }
    }
}

How can I restrict touristBIRTHDAY to be +18 years old? I think that I have to use this function, but I don't know where to put it: Note: this function it's an example.

DateTime bday = DateTime.Parse(dob_main.Text);
DateTime today = DateTime.Today;
int age = today.Year - bday.Year;
if(age < 18)
{
    MessageBox.Show("Invalid Birth Day");
}

Thanks ;)

UPDATE: I follow the solution of Berkay Yaylaci, but I'm getting a NullReferenceException. It's seems that my value parameter is default, and then my method is not posting, why? What is the solution to that?

Answer 1

You can write your own Validation. First, create a class.

I called MinAge.cs

 public class MinAge : ValidationAttribute
    {
        private int _Limit;
        public MinAge(int Limit) { // The constructor which we use in modal.
            this._Limit = Limit;
        }
        protected override ValidationResult IsValid(object value, ValidationContext validationContext) 
        {
                DateTime bday = DateTime.Parse(value.ToString());
                DateTime today = DateTime.Today;
                int age = today.Year - bday.Year;
                if (bday > today.AddYears(-age))
                {
                   age--; 
                }
                if (age < _Limit)
                {
                    var result = new ValidationResult("Sorry you are not old enough");
                    return result; 
                }
               
            
            return null;

        }
    }

SampleModal.cs

[MinAge(18)] // 18 is the parameter of constructor. 
public DateTime UserBirthDate { get; set; }

IsValid runs after post and check the Limit. If age is not greater than the Limit (which we gave in modal!) than return ValidationResult