While many of the URI operations are unavailable for [`UriKind.Relative`][2] (for whatever reason), you can build a fully qualified URI through one of the [overloads][0] that takes in a Base URI

Here's an example [from the docs on `Uri.Query`][1]:

```cs
Uri baseUri = new Uri ("http://www.contoso.com/");
Uri myUri = new Uri (baseUri, "catalog/shownew.htm?date=today");

Console.WriteLine(myUri.Query); // date=today
```

You can also get the current base from [`HttpContext.Current.Request.Url`][3] or even just create a mock URI base with `"http://localhost"` if all you care about is the path components.

So either of the following approaches should also return the QueryString from a relative path:


```cs
var path = "catalog/shownew.htm?date=today"
var query1 = new Uri(HttpContext.Current.Request.Url, path).Query;
var query2 = new Uri(new Uri("http://localhost"), path).Query;
```



[0]: https://learn.microsoft.com/en-us/dotnet/api/system.uri.-ctor?view=netframework-4.7.2
[1]:
https://learn.microsoft.com/en-us/dotnet/api/system.uri.query?view=netframework-4.7.2

[2]: https://learn.microsoft.com/en-us/dotnet/api/system.urikind?view=netframework-4.7.2
[3]: https://learn.microsoft.com/en-us/dotnet/api/system.web.httprequest.url?view=netframework-4.7.2

What's the most efficient way to get a specific parameter from a relative URL string using C#?

For example, how would you get the value of the `ACTION` parameter from the following relative URL string:

    string url = "/page/example?ACTION=data&FOO=test";

I have already tried using:

    var myUri = new Uri(url, UriKind.Relative);
    String action = HttpUtility.ParseQueryString(myUri.Query).Get("ACTION");

However, I get the following error: 

> This operation is not supported for a relative URI.

