How do you test your Request.QueryString[] variables?

Question

I frequently make use of Request.QueryString[] variables.

In my Page_load I often do things like:

       int id = -1;

        if (Request.QueryString["id"] != null) {
            try
            {
                id = int.Parse(Request.QueryString["id"]);
            }
            catch
            {
                // deal with it
            }
        }

        DoSomethingSpectacularNow(id);

It all seems a bit clunky and rubbish. How do you deal with your Request.QueryString[]s?

Answer 1

Below is an extension method that will allow you to write code like this:

int id = request.QueryString.GetValue<int>("id");
DateTime date = request.QueryString.GetValue<DateTime>("date");

It makes use of TypeDescriptor to perform the conversion. Based on your needs, you could add an overload which takes a default value instead of throwing an exception:

public static T GetValue<T>(this NameValueCollection collection, string key)
{
    if(collection == null)
    {
        throw new ArgumentNullException("collection");
    }

    var value = collection[key];

    if(value == null)
    {
        throw new ArgumentOutOfRangeException("key");
    }

    var converter = TypeDescriptor.GetConverter(typeof(T));

    if(!converter.CanConvertFrom(typeof(string)))
    {
        throw new ArgumentException(String.Format("Cannot convert '{0}' to {1}", value, typeof(T)));
    }

    return (T) converter.ConvertFrom(value);
}