ASP.NET MVC - Create action link preserve query string

Question

I am currently writing my own paged list for ASP.NET Core MVC.

I struggle while creating the following:

I want to create a UrlHelper extension method: Url.PageLink(int page, int pageSize)

Within that extension method I want to return a link which reuses ALL current values for controller, action, querystring and in addition it should add/update the page, pageSize values in the querystring as well.

Questions: From where do I get the current controller and action in the UrlHelper object? What is the best way to rebuild the querystring? I can see it here url.ActionContext.HttpContext.Request.QueryString... but do I really have to manually rebuild it? Or does something like AddQueryStringValue(int key, object value) exist?

Thanks so much in advance!!! Simon

Answer 1

Improvement of Simon's answer: It can be called as @Url.Current(new {page=42, id=5, foo=bar}) It will preserve query string and update/add provided values.

public static class UrlHelperExtensions
    {
        /// <summary>
        /// Get current URL with substituted values while preserving query string
        /// </summary>
        /// <param name="helper"></param>
        /// <param name="substitutes">Query string parameters or route data paremers. E.g. new { action="Index", sort = "asc"}</param>
        /// <returns></returns>
        public static string Current(this IUrlHelper helper, object substitutes)
        {
            RouteValueDictionary routeData = new RouteValueDictionary(helper.ActionContext.RouteData.Values);
            IQueryCollection queryString = helper.ActionContext.HttpContext.Request.Query;

            //add query string parameters to the route data
            foreach (var param in queryString)
            {
                if (!string.IsNullOrEmpty(queryString[param.Key]))
                {
                    //rd[param.Key] = qs[param.Value]; // does not assign the values!
                    routeData.Add(param.Key, param.Value);
                }
            }

            // override parameters we're changing in the route data
            //The unmatched parameters will be added as query string.
            foreach (PropertyDescriptor property in TypeDescriptor.GetProperties(substitutes.GetType()))
            {
                var value = property.GetValue(substitutes);
                if (string.IsNullOrEmpty(value.ToString()))
                {
                    routeData.Remove(property.Name);
                }
                else
                {
                    routeData[property.Name] = value;
                }
            }

            string url = helper.RouteUrl(routeData);
            return url;
        }
    }

Answer 2

The question asks for Asp.Net Core. I was trying to use shturm's answer on MVC 5 and could not get it to work. I took his same concepts and changed it to work with MVC 5. If anyone needs this verison, I'm posting it here. I also added the ability to change the action and controller.

    /// <summary>
    /// Get URL with substituted values while preserving query string.
    /// </summary>
    /// <param name="helper">The url helper object we are extending.</param>
    /// <param name="action">The action we want to direct to.</param>
    /// <param name="controller">The controller we want to direct to.</param>
    /// <param name="substitutes">Query string parameters or route data paremers. E.g. new { action="Index", sort = "asc"}</param>
    /// <returns>The route string.</returns>
    public static String ActionWithOriginalQueryString(this UrlHelper helper, String action, String controller, object substitutes)
    {            
        RouteValueDictionary routeData = new RouteValueDictionary(helper.RequestContext.RouteData.Values);
        NameValueCollection queryString = helper.RequestContext.HttpContext.Request.QueryString;

        //add query string parameters to the route data
        foreach (var param in queryString.AllKeys)
        {
            if (!string.IsNullOrEmpty(queryString[param]))
            {
                //rd[param.Key] = qs[param.Value]; // does not assign the values!
                routeData.Add(param, queryString[param]);
            }
        }

        // override parameters we're changing in the route data
        //The unmatched parameters will be added as query string.
        foreach (PropertyDescriptor property in TypeDescriptor.GetProperties(substitutes.GetType()))
        {
            var value = property.GetValue(substitutes);
            if (string.IsNullOrEmpty(value?.ToString()))
            {
                routeData.Remove(property.Name);
            }
            else
            {
                routeData[property.Name] = value;
            }
        }

        //Set the controller and the action.
        routeData["controller"] = controller;
        routeData["action"] = action;

        //Return the route.
        return helper.RouteUrl(routeData);
    }