Automatically Breaking Js and Css Cache Using Build Number in Asp.Net

MyExtensions.cs

public static string BuildNumber(this HtmlHelper html)
{
    if (html.ViewContext.HttpContext.Cache["_buildnumber_"] == null)
    {
        var version = System.Reflection.Assembly
            .GetExecutingAssembly().GetName().Version;
        html.ViewContext.HttpContext.Cache["_buildnumber_"] = 
            version.Build.ToString();
    }
    return html.ViewContext.HttpContext.Cache["_buildnumber_"].ToString();
}