How to do string "not like" validation in view model in ASP.NET MVC5?

Question

So what I like to do is:

   [NotLike(Value = "Forbidden value")]
   public string Title { get; set; }
 

Is it possible? I've read the docs from Microsoft and could not find anything like this.

Answer 1

You should be using ValidationAttribute and inherit from it as follows:

 public class NotLikeAttribute : ValidationAttribute
{
    private string _NotLikeStr = "";
    public NotLikeAttribute(string notLikeStr)
    {
        this._NotLikeStr = notLikeStr;
    }
    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        if (value != null)
        {
            if (!((string)value).Contains(_NotLikeStr))
            {
                var memberName = validationContext.MemberName;
                var errorMsg = "Your Message";
                return new ValidationResult(errorMsg);
            }
        }
        return null;
    }
}

and decorate your property as follows:

 [NotLike("Forbidden value")]
   public string Title { get; set; }

of course instead of using line below

 if (!((string)value).Contains(_NotLikeStr))

you can split string to multiple words or use Regular expression or anything that meets your requirements .

Answer 2

I have two solution for you question:

1. Use [RegularExpression()]

You can use regular expression and create your own pattern for validation

For more information have a look at this link: Data annotation regular expression

2. Create new Custom Data annotation

You can create new custom data annotation (like what you did in question)

For more information have a look at this link: How to create Custom Data Annotation Validators

Answer 3

You can use regular expression for this

[RegularExpression(@"^((?!Forbidden value).)*$", ErrorMessage = "Characters are not allowed.")]
public string Title { get; set; }