Validate a string to be one of two lengths - asp.net-mvc

Question

Is it possible to use ASP MVC's DataAnnotation to require a string to be one of two lengths? This example obviously doesn't work but I am thinking of something along these lines
[Required]
[DisplayName("Agent ID")]
[StringLength(8) || StringLength(10)]
public string AgentId

Answer 1

You can write your own validation attribute to handle it:
public class UserStringLengthAttribute : ValidationAttribute
{
private int _lenght1;
private int _lenght2;
public UserStringLengthAttribute(int lenght2, int lenght1)
{
_lenght2 = lenght2;
_lenght1 = lenght1;
}
public override bool IsValid(object value)
{
var typedvalue = (string) value;
if (typedvalue.Length != _lenght1 || typedvalue.Length != _lenght2)
{
ErrorMessage = string.Format("Length should be {0} or {1}", _lenght1, _lenght2);
return false;
}
return true;
}
}
And use it:
[Required]
[DisplayName("Agent ID")]
[UserStringLength(8,10)]
public string AgentId

Answer 2

Yes you can do that . Do a custom validator that inherits from StringLength and this will work for both client and server side
public class CustomStringLengthAttribute : StringLengthAttribute
{
private readonly int _firstLength;
private readonly int _secondLength;
public CustomStringLengthAttribute(int firstLength, int secondLength)
: base(firstLength)
{
_firstLength = firstLength;
_secondLength = secondLength;
}
public override bool IsValid(object value)
{
int valueTobeValidate = value.ToString().Length;
if (valueTobeValidate == _firstLength)
{
return base.IsValid(value);
}
if (valueTobeValidate == _secondLength)
{
return true;
}
return base.IsValid(value);
}
}
and register the adapter in the Appplication_start of the Global.asax.cs
DataAnnotationsModelValidatorProvider.RegisterAdapter(typeof(CustomStringLengthAttribute), typeof(StringLengthAttributeAdapter));