(Asp.Net MVC3) How to Define StringLength for ASCII and Unicode?

Question

I have following define in model

        [Required]
        [StringLength(100, MinimumLength = 10)]
        [DataType(DataType.Text)]
        [Display(Name = "XXX")]
        public string XXX{ get; set; }

Now I want it treat ACSII and Unicode input differently, for ASCII, each char consider length 1, so need min-length 10 and max length 50. But for Unicode char, I want to consider it length 2, so 5 unicode chars is enough for the minimal requirement.

How do I do it?

I guess I might need two approach, first overwrite the length check in asp.net, then I need to overwite the length check in jquery. Isn't it?

Is anyone here have a working sample, thanks.

Answer 1

To do what you want, you should be able to introduce a custom validation attribute:

class FooAttribute : ValidationAttribute
{
    private readonly int minLength, maxLength;
    public FooAttribute(int minLength, int maxLength) : this(minLength, maxLength, "Invalid ASCII/unicode string-length") {}
    public FooAttribute(int minLength, int maxLength, string errorMessage) : base(errorMessage)
    {
        this.minLength = minLength;
        this.maxLength = maxLength;
    }

    protected override ValidationResult IsValid(object value, ValidationContext ctx)
    {
        if(value == null) return ValidationResult.Success;
        var s = value as string;
        if(s == null) return new ValidationResult("Not a string");

        bool hasNonAscii = s.Any(c => c >= 128);

        int effectiveLength = hasNonAscii ? (2*s.Length) : s.Length;

        if(effectiveLength < minLength || effectiveLength > maxLength) return new ValidationResult(FormatErrorMessage(ctx.DisplayName));
        return ValidationResult.Success;
    }
}