asp.net mvc validation on 2 fields - one must exist if other entered

Question

I have 2 text fields, text1 and text2, in my view model. I need to validate if text1 is entered then text2 must be entered and vice versa. How can this be achieved in the custom validation in the view model?

thanks.

Answer 1

You can use implement IValidatableObject (from System.ComponentModel.DataAnnotations namespace) for the server side validation on your View Model:

public class AClass : IValidatableObject 
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string SecondName { get; set; }
        public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
        {
            if( (!string.IsNullOrEmpty(Name) && string.IsNullOrEmpty(SecondName)) || (string.IsNullOrEmpty(Name) && !string.IsNullOrEmpty(SecondName)) )
                yield return new ValidationResult("Name and Second Name should be either filled, or null",new[] {"Name","SecondName"});
        }
    }

Now it make sure if both Name and SecondName are set, or null, then model is valid, otherwise, it's not.