ASP.NET MVC 5: EmailAddress attribute custom error message

Question

In register form I use EmailAddress attribute to validate user email.

public class RegisterViewModel
{
    [Required(ErrorMessage = "Pole wymagane")]
    [Display(Name = "Email")]
    [DataType(DataType.EmailAddress)]
    [EmailAddress]
    public string Email { get; set; }
}

Is there any chance to show what is wrong with email address if validation fails? For example 'oops, I see that your email address contains whitespace'

Answer 1

You have to add another validation for that. Example using [RegularExpression]

public class RegisterViewModel
{
    [Required(ErrorMessage = "Pole wymagane")]
    [RegularExpression(@"^\S*$", ErrorMessage = "Email Address cannot have white spaces")]
    [Display(Name = "Email")]
    [DataType(DataType.EmailAddress)]
    [EmailAddress]
    public string Email { get; set; }
}

Answer 2

You can define your own regular expression for email:

// built-in [EmailAddress] does not allow white spaces around email
public const string EmailValidationRegEx = @"^\s*\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*\s*$"; 

Note: I have just added white spaces around the existing .NET regex pattern for email match: "^\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*$"

Now you can use this new regex pattern instead of [EmailAddress] attribute:

public class RegisterViewModel
{
    private string _email;

    [Required(ErrorMessage = "Pole wymagane")]
    [Display(Name = "Email")]
    [DataType(DataType.EmailAddress)]
    [RegularExpressionWithOptions(EmailValidationRegEx, ErrorMessage = "Invalid email")]
    public string Email 
    { 
        get => _email;

        set
        {
            _email = string.IsNullOrEmpty(value) ? string.Empty : value.Trim();
        }
    }
}

Note that I have modified the setter to trim() the value. This ensures that we always get rid of extra white spaces before using the email value.