How to build a query string for a URL in C#?

A common task when calling web resources from a code is building a query string to including all the necessary parameters. While by all means no rocket science, there are some nifty details you need to take care of like, appending an & if not the first parameter, encoding the parameters etc.

The code to do it is very simple, but a bit tedious:

StringBuilder SB = new StringBuilder();
if (NeedsToAddParameter A) 
{ 
  SB.Append("A="); SB.Append(HttpUtility.UrlEncode("TheValueOfA")); 
}

if (NeedsToAddParameter B) 
{
  if (SB.Length>0) SB.Append("&"); 
  SB.Append("B="); SB.Append(HttpUtility.UrlEncode("TheValueOfB")); }
}

This is such a common task one would expect a utility class to exist that makes it more elegant and readable. Scanning MSDN, I failed to find one—which brings me to the following question:

What is the most elegant clean way you know of doing the above?

If you look under the hood the QueryString property is a NameValueCollection. When I've done similar things I've usually been interested in serialising AND deserialising so my suggestion is to build a NameValueCollection up and then pass to:

using System.Linq;
using System.Web;
using System.Collections.Specialized;

private string ToQueryString(NameValueCollection nvc)
{
    var array = (
        from key in nvc.AllKeys
        from value in nvc.GetValues(key)
            select string.Format(
                "{0}={1}",
                HttpUtility.UrlEncode(key),
                HttpUtility.UrlEncode(value))
        ).ToArray();
    return "?" + string.Join("&", array);
}

I imagine there's a super elegant way to do this in LINQ too...

Stack Overflow Q#829080, score: 330