Change Single URL query string value

Question

I have an ASP.NET page which takes a number of parameters in the query string:

search.aspx?q=123&source=WebSearch

This would display th

Answer 1

Using this QueryStringBuilder helper class, you can grab the current QueryString and call the Add method to change an existing key/value pair...

//before: "?id=123&page=1&sessionId=ABC"
string newQueryString = QueryString.Current.Add("page", "2");
//after: "?id=123&page=2&sessionId=ABC"

Answer 2

Use the URIBuilder Specifically the link textQuery property

I believe that does what you need.

Answer 3

You can't modify the QueryString directly as it is readonly. You will need to get the values, modify them, then put them back together. Try this:

var nameValues = HttpUtility.ParseQueryString(Request.QueryString.ToString());
nameValues.Set("page", "2");
string url = Request.Url.AbsolutePath;
string updatedQueryString = "?" + nameValues.ToString();
Response.Redirect(url + updatedQueryString);

The ParseQueryString method returns a NameValueCollection (actually it really returns a HttpValueCollection which encodes the results, as I mention in an answer to another question). You can then use the Set method to update a value. You can also use the Add method to add a new one, or Remove to remove a value. Finally, calling ToString() on the name NameValueCollection returns the name value pairs in a name1=value1&name2=value2 querystring ready format. Once you have that append it to the URL and redirect.

Alternately, you can add a new key, or modify an existing one, using the indexer:

nameValues["temp"] = "hello!"; // add "temp" if it didn't exist
nameValues["temp"] = "hello, world!"; // overwrite "temp"
nameValues.Remove("temp"); // can't remove via indexer

You may need to add a using System.Collections.Specialized; to make use of the NameValueCollection class.

Answer 4

You can do this without all the overhead of redirection (which is not inconsiderable). My personal preference is to work with a NameValueCollection which a querystring really is, but using reflection:

// reflect to readonly property 
PropertyInfo isReadOnly = typeof(System.Collections.Specialized.NameValueCollection).GetProperty("IsReadOnly", BindingFlags.Instance | BindingFlags.NonPublic); 

// make collection editable 
isReadOnly.SetValue(this.Request.QueryString, false, null); 

// remove 
this.Request.QueryString.Remove("foo"); 

// modify 
this.Request.QueryString.Set("bar", "123"); 

// make collection readonly again 
isReadOnly.SetValue(this.Request.QueryString, true, null); 

Answer 5

This is pretty arbitrary, in .NET Core at least. And it all boils down to asp-all-route-data

Consider the following trivial example (taken from the "paginator" view model I use in virtually every project):

public class SomeViewModel 
{

    public Dictionary<string, string> NextPageLink(IQueryCollection query)
    {
        /*
         * NOTE: how you derive the "2" is fully up to you
         */
        return ParseQueryCollection(query, "page", "2");
    }

    Dictionary<string, string> ParseQueryCollection(IQueryCollection query, string replacementKey, string replacementValue)
    {
        var dict = new Dictionary<string, string>()
        {
            { replacementKey, replacementValue }
        };

        foreach (var q in query)
        {
            if (!string.Equals(q.Key, replacementKey, StringComparison.OrdinalIgnoreCase))
            {
                dict.Add(q.Key, q.Value);
            }
        }

        return dict;
    }
}

Then to use in your view, simply pass the method the current request query collection from Context.Request:

<a asp-all-route-data="@Model.NextPageLink(Context.Request.Query)">Next</a>