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

Question

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 so

Answer 1

I wrote a helper for my razor project using some of the hints from other answers.

The ParseQueryString business is necessary because we are not allowed to tamper with the QueryString object of the current request.

@helper GetQueryStringWithValue(string key, string value) {
    var queryString = System.Web.HttpUtility.ParseQueryString(HttpContext.Current.Request.QueryString.ToString());
    queryString[key] = value;
    @Html.Raw(queryString.ToString())
}

I use it like this:

location.search = '?@Helpers.GetQueryStringWithValue("var-name", "var-value")';

If you want it to take more than one value, just change the parameters to a Dictionary and add the pairs to the query string.