Validation of List<string> via regex in model annotation

Question

I'm working with asp.net mvc 5. I have a List<string> like this:

var animals = new List<string>
{
   "Dog",
   "Cat"
};

animals can contain only 2 values: Dog and Cat . So, that's invalid if the value is Tiger or Lion .

Here is the basic way I've used to validate:

var regex = new Regex(@"Dog|Cat");
foreach (string animal in animals)
{
   if (!regex.IsMatch(animal))
   {
      // throw error message here...
   }
}

Now, I want to declare a model Animal to store the List:

class Animal
{
   //[RegularExpression(@"Dog|Cat", ErrorMessage = "Invalid animal")]
   public List<string> Animals { get; set; }
}

and in some action:

public ActionResult Add(Animal model)
{
   if (ModelState.IsValid)
   {
      // do stuff...
   }
   // throw error message...
}

So, my question is: how to use regex to validate the value of List<string> in this case?

Answer 1

Based on diiN's answer :

public class RegularExpressionListAttribute : RegularExpressionAttribute
{
    public RegularExpressionListAttribute(string pattern)
        : base(pattern) { }

    public override bool IsValid(object value)
    {
        if (value is not IEnumerable<string>)
            return false;

        foreach (var val in value as IEnumerable<string>)
        {
            if (!Regex.IsMatch(val, Pattern))
                return false;
        }

        return true;
    }
}

Usage:

[RegularExpressionList("your pattern", ErrorMessage = "your message")]
public List<string> Animals { get; set; }

Answer 2

You could write your own attribute:

public class ListIsValid : ValidationAttribute
{
    public override bool IsValid(List animals)
    {
        var regex = new Regex(@"Dog|Cat");
        foreach (string animal in animals)
        {
            if (!regex.IsMatch(animal))
            {
                return false;
            }
        }
        return true;
    }
}

In your Animal class you then use it like this:

[ListIsValid(ErrorMessage = "There is some wrong animal in the list")]
public List<string> Animals { get; set; }

Answer 3

Define custom Validation attribute and implement your custom logic there.

public class OnlyDogsAndCatsAttribute : ValidationAttribute
{
    public override bool IsValid(object value)
    => (value as IList<string>).All(s => s == "Dog" || s == "Cat"); 
}

public class Animal
{
   [OnlyDogsAndCatsAttribute]
   public List<string> Animals { get; set; }
}

Notice no need to use regex