Best way to convert query string to dictionary in C#

HttpUtility.ParseQueryString() parses query string into a NameValueCollection object, converting the latter to an IDictionary<string, string> is a matter of a simple foreach. This, however, might be unnecessary since NameValueCollection has an indexer, so it behaves pretty much like a dictionary.

Here is how I usually do it

Dictionary<string, string> parameters = HttpContext.Current.Request.QueryString.Keys.Cast<string>()
    .ToDictionary(k => k, v => HttpContext.Current.Request.QueryString[v]);

How about HttpUtility.ParseQueryString?

Just add a reference to System.Web.dll

Same as Sean, but with Linq (and a function you can copy and paste):

public static Dictionary<string, string> ParseQueryString(string queryString)
{
   var nvc = HttpUtility.ParseQueryString(queryString);
   return nvc.AllKeys.ToDictionary(k => k, k => nvc[k]);
}

Also, the question asked how to get it back into a query string:

public static string CreateQueryString(Dictionary<string, string> parameters)
{
   return string.Join("&", parameters.Select(kvp => 
      string.Format("{0}={1}", kvp.Key, HttpUtility.UrlEncode(kvp.Value))));
}

Just had to do this for a mono compatible solution

Regex.Matches(queryString, "([^?=&]+)(=([^&]*))?").Cast<Match>().ToDictionary(x => x.Groups[1].Value, x => x.Groups[3].Value)

In ASP.NET Core, use ParseQuery.

var query = HttpContext.Request.QueryString.Value;
var queryDictionary = Microsoft.AspNetCore.WebUtilities.QueryHelpers.ParseQuery(query);

One liner without HttpUtility

var dictionary = query.Replace("?", "").Split('&').ToDictionary(x => x.Split('=')[0], x => x.Split('=')[1]);

I like the brevity of Jon Canning's answer, but in the interest of variety, here is another alternative to his answer, that would also work for restricted environments like Windows Phone 8, that lack the HttpUtility.ParseQueryString() utility:

    public static Dictionary<string, string> ParseQueryString(String query)
    {
        Dictionary<String, String> queryDict = new Dictionary<string, string>();
        foreach (String token in query.TrimStart(new char[] { '?' }).Split(new char[] { '&' }, StringSplitOptions.RemoveEmptyEntries))
        {
            string[] parts = token.Split(new char[] { '=' }, StringSplitOptions.RemoveEmptyEntries);
            if (parts.Length == 2)
                queryDict[parts[0].Trim()] = HttpUtility.UrlDecode(parts[1]).Trim();
            else
                queryDict[parts[0].Trim()] = "";
        }
        return queryDict;
    }

Actually, a useful improvement to Canning's answer that take care of decoding url-encoded values (like in the above solution) is:

    public static Dictionary<string, string> ParseQueryString2(String query)
    {
       return Regex.Matches(query, "([^?=&]+)(=([^&]*))?").Cast<Match>().ToDictionary(x => x.Groups[1].Value, x => HttpUtility.UrlDecode( x.Groups[3].Value ));
    }

Yet another way to do it:

NameValueCollection nvcData = HttpUtility.ParseQueryString(queryString);
Dictionary<string, string> dictData = new Dictionary<string, string>(nvcData.Count);
foreach (string key in nvcData.AllKeys)
{
    dictData.Add(key, nvcData.Get(key));
}

You can just get it by decorating the parameter with the FromQueryAttribute

public void Action([FromQuery] Dictionary<string, string> queries)
{
    ...
}

P.S. If you want to get multiple values for each key you can change the Dictionary to Dictionary<string, List<string>>

Most simple:

Dictionary<string, string> parameters = new Dictionary<string, string>();

for (int i = 0; i < context.Request.QueryString.Count; i++)
{
    parameters.Add(context.Request.QueryString.GetKey(i), context.Request.QueryString[i]);
}

I stumbled across this post whilst looking for the same solution for an Azure WebJob, hopefully this helps others doing the same.

If you are coding an Azure WebJob you use the GetQueryParameterDictionary() extension method.

var queryParameterDictionary = request.GetQueryParameterDictionary();

where request is of type HttpRequest and queryParameterDictionary is now of type IDictionary<string, string>

Instead of converting HttpContext.Request.QueryString to Dictionary<>, try using

HttpContext.Request.Query

which already is a Dictionary<string, StringValues>

AspNet Core now automatically includes HttpRequest.Query which can be used similar to a dictionary with key accessors like this:

var x = Current.Request.Query["x"];

However if you needed to cast it for logging or other purposes, you can pull out that logic into an extension method like this:

public static class HttpRequestExtensions
{
  public static Dictionary<string, string> ToDictionary(this IQueryCollection query)
  {
    return query.Keys.ToDictionary(k => k, v => (string)query[v]);
  }
}

Then, you can consume it on your httpRequest like this:

var queryParams = Current.Request.Query.ToDictionary()

Further Reading

• How to parse a query string into a NameValueCollection in .NET
• Convert query string to key-value pair in .Net
• Is it possible to get Dictionary from query string?