Web Api validating optional Url with DataAnnotations

Question

Is there a way to make the [Url] validation optional?

As an example

public class Company 
{
        [Required, StringLength(63, MinimumLength = 2)]
        public string Name { get; set; }

        [Url, StringLength(127)]
        public string Url { get; set; }
}

The above validation works exactly as i intended it to with the exception that the Url property cannot be optional. I don't want the validation to throw an error if it is blank rather I just want it to validate only when a user enters a value.

UPDATE: Taking into consideration the answer below from Hamid Shahid. I just added a condition to work around my issue until something better comes up:

        //Making url validation optional, fix
        if (company.Url == string.Empty) company.Url = null;

Hamid Shahid · Accepted Answer · 2017-11-09 18:54:16Z

4

The URLAttribute validation returns true for null value. If the URL property has a value of NULL, it would be considered as a valid value. If you are setting it to an empty string, it would be considered invalid.

The code below show decompiled version of UrlAttribute class

// System.ComponentModel.DataAnnotations.UrlAttribute
[__DynamicallyInvokable]
public override bool IsValid(object value)
{
    if (value == null)
    {
        return true;
    }
    string text = value as string;
    if (UrlAttribute._regex != null)
    {
        return text != null && UrlAttribute._regex.Match(text).Length > 0;
    }
    return text != null && (text.StartsWith("http://", StringComparison.InvariantCultureIgnoreCase) || text.StartsWith("https://", StringComparison.InvariantCultureIgnoreCase) || text.StartsWith("ftp://", StringComparison.InvariantCultureIgnoreCase));
}

edited Nov 9, 2017 at 18:54

answered Nov 9, 2017 at 17:55

Hamid Shahid

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3 Comments

DonO Over a year ago

That is true, is there any way i can make it work for empty string ?

Hamid Shahid Over a year ago

No with out of the box functionality. You can write your own custom class if you like

Hamid Shahid Over a year ago

@DonO if you like, can you please mark it as answer

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