MVC DataAnnotation Accept No Spaces - asp.net-mvc

Question

I'm developing a Login View in MVC5.
I would like to set at the ViewModel level a DataAnnotation to state the the field does NOT accept empty spaces.
Is there a Data Annotation in MVC (something like [NoSpaces] that can be used to NOT allow a string field to contain "spaces" ?

Answer 1

How about this:
[RegularExpression(#"^\S*$", ErrorMessage = "No white space allowed")]

Answer 2

Well, the simplest but robust thing I can think of is to look at how existing code works, or how existing data annotation work.
For example, let's look at the System.ComponentModel.DataAnnotations.StringLengthAttribute class.
Here's the definition only (just to keep short):
namespace System.ComponentModel.DataAnnotations
{
[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter, AllowMultiple = false)]
public class StringLengthAttribute : ValidationAttribute
{
public StringLengthAttribute(int maximumLength);
public int MinimumLength { get; set; }
public override string FormatErrorMessage(string name);
public override bool IsValid(object value);
}
}
So I would simply copy the original implementation source code from GitHub and customize it to my needs. For example, to obtain a signature like this (if I understood correctly and this is what you wanted):
public StringLengthAttribute(int maximumLength, int minLength = 0, allowEmptySpaces = true);
For more in-depth info, I would also read the Microsoft docs on the ValidationAttribute class, which is your base class for custom validation data annotations.
EDIT:
I would NOT rely on Regular Expressions to validate data in cases where I just need to exclude empty strings or strings containing only white space(s), because Regular Expressions are very expensive to process (and require a lot of memory allocation, because of an expression compiler, a state machine, etc.).

Answer 3

If this is convenient for anyone, I got pass this issue by doing this on the client:
//trim each form input
var $form = $("#myForm");
$form.find("input:text").each(function(){
var $self= $(this);
$self.va($self.val().trim());
});
//then validate before submit
if($form.valid()){ $form.submit(); }
// on the server ModelState.Isvalid does verify each item with [Required] and won't accept only white spaces from an input (but this means additional roundtrip to server and it's not always convenient)