MVC DataAnnotation Accept No Spaces

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" ?

You want the RegularExpression validator. http://msdn.microsoft.com/en-us/library/system.componentmodel.dataannotations.regularexpressionattribute(v=vs.110).aspx I am nut good with regular expressions, but this validator is the one you need. — Nigel Ellis, Oct 30 '14 at 16:48

score 39 · Accepted Answer · edited Jul 14 '17 at 15:29

39

How about this:

[RegularExpression(@"^\S*$", ErrorMessage = "No white space allowed")]

edited Jul 14 '17 at 15:29

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answered Oct 30 '14 at 16:53

Kirby

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...that will allow any character but spaces, is that right? – SF Developer Oct 30 '14 at 16:54
From msdn - Matches any non-white-space character. – Kirby Oct 30 '14 at 16:55
If you find yourself using a DataAnnotation like this in multiple places, it can be handy to make a custom class that inherits from RegularExpressionAttribute and just has an empty constructor that passes the parameters you are using into the base constructor. – Justin Ryder Oct 30 '14 at 20:00
This is very expensive and does not follow DRY. There is a more performant way. Check my answer. – Paul-Sebastian Manole Jun 09 '21 at 18:54

score 1 · Answer 2 · answered Jun 09 '21 at 18:48

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.).

score 0 · Answer 3 · answered Oct 22 '20 at 10:43

0

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)

answered Oct 22 '20 at 10:43

sTx

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This is not a good practice to do it at the client side. It will work fine as long as you control the client, but if someone would send e request in a different way, your server won't even handle this scenario. Server should implement that check ALWAYS.. – infografnet Nov 19 '20 at 11:14

MVC DataAnnotation Accept No Spaces

3 Answers3