Easiest way to parse "querystring" formatted data

Question

With the following code:

string q = "userID=16555&gameID=60&score=4542.122&time=343114";

What would be the easiest way to parse the values, preferably without writing my own parser? I'm looking for something with the same functionality as Request.querystring["gameID"].

Galantine

Answer 1

Pretty easy... use the HttpUtility.ParseQueryString method.

Untested, but this should work:

var qs = "userID=16555&gameID=60&score=4542.122&time=343114";
var parsed = HttpUtility.ParseQueryString(qs);
var userId = parsed["userID"]; 
//  ^^^^^^ Should be "16555".  Note this will be a string of course.

Andersen

Thanks! Looks good, I'm having trouble decoding the horrible example they provided on the MSDN page though, once I have var q = HttpUtility.ParseQueryString("?userID=16555&gameID=60&score=4542.122&time=343114"); how do I retrieve a specific value? – Galantine

I can't find System.Net.HttpUtility net Core 1.0 framework – License

Seems like they removed it. Reference the answer here for a solution: #29993348 – Andersen

The Nancy library also includes Nancy.Helpers.HttpUtility.ParseQueryString. – Barbi

Note that ParseQueryString fails is there is more than 1024 key-value pairs in the string. – Quenna

@Quenna if you’ve got 1025 keys in a query string, I’d argue that you’ve got bigger problems 😉 – Andersen

@ChrisShain Well, there is e.g. one Paypal API that returns transactions data as a huge url-encoded string of key-value pairs. It easily exceeds 1024. – Quenna

Answer 2

You can do it with linq like this.

string query = "id=3123123&userId=44423&format=json";

Dictionary<string,string> dicQueryString = 
        query.Split('&')
             .ToDictionary(c => c.Split('=')[0],
                           c => Uri.UnescapeDataString(c.Split('=')[1]));

string userId = dicQueryString["userID"];

Edit

If you can use HttpUtility.ParseQueryString then it will be a lot more straight forward and it wont be case-sensitive as in case of LinQ.

Kerns

That works in this specific case, but it's not a generic solution because it doesn't do percent-decoding. – Fall

Right @Francis Avila, then it will need more modification in query. – Kerns

This is a good solution if you need to parse query strings outside of the System.Web context. – Dna

This preserves case, unlike ParseQueryString. – Piggin

And what happens when you have a query string like a=1&a=2&a=3? That is valid, as is a=1;a=2;a=3. Use HttpUtility.ParseQueryString. It handles these and other oddities. – Fisk

I came here because HttpUtility.ParseQueryString() performed the decoding. this solution here works for me. – Malkin

@JimMischel to .ToLookup rather than .ToDictionary to handle "duplicate keys" – Compensatory

Answer 3

As has been mentioned in each of the previous answers, if you are in a context where you can add a dependency to the System.Web library, using HttpUtility.ParseQueryString makes sense. (For reference, the relevant source can be found in the Microsoft Reference Source). However, if this is not possible, I would like to propose the following modification to Adil's answer which accounts for many of the concerns addressed in the comments (such as case sensitivity and duplicate keys):

var q = "userID=16555&gameID=60&score=4542.122&time=343114";
var parsed = q.TrimStart('?')
    .Split(new[] { '&' }, StringSplitOptions.RemoveEmptyEntries)
    .Select(k => k.Split('='))
    .Where(k => k.Length == 2)
    .ToLookup(a => a[0], a => Uri.UnescapeDataString(a[1])
      , StringComparer.OrdinalIgnoreCase);
var userId = parsed["userID"].FirstOrDefault();
var time = parsed["TIME"].Select(v => (int?)int.Parse(v)).FirstOrDefault();

Telestich

Ignores single item arguments, which can sometimes also appear: arg1&arg2&arg3 – Arbour

Answer 4

If you want to avoid the dependency on System.Web that is required to use HttpUtility.ParseQueryString, you could use the Uri extension method ParseQueryString found in System.Net.Http.

Note that you have to convert the response body to a valid Uri so that ParseQueryString works.

Please also note in the MSDN document, this method is an extension method for the Uri class, so you need reference the assembly System.Net.Http.Formatting (in System.Net.Http.Formatting.dll). I tried installed it by the nuget package with the name "System.Net.Http.Formatting", and it works fine.

string body = "value1=randomvalue1&value2=randomValue2";

// "http://localhost/query?" is added to the string "body" in order to create a valid Uri.
string urlBody = "http://localhost/query?" + body;
NameValueCollection coll = new Uri(urlBody).ParseQueryString();

Farfetched

Not sure this works...Uri doesn't have a ParseQueryString method attached to it when I try this, my code: var collection = new System.Uri(url).ParseQueryString(); – Delinda

@TrevorHart Did you make sure to add a reference to System.Net.Http and to add the System.Net.Http namespace? – Farfetched

I did, I ended up just writing my own parser. – Delinda

Answer 5

How is this

using System.Text.RegularExpressions;

// query example
//   "name1=value1&name2=value2&name3=value3"
//   "?name1=value1&name2=value2&name3=value3"
private Dictionary<string, string> ParseQuery(string query)
{
    var dic = new Dictionary<string, string>();
    var reg = new Regex("(?:[?&]|^)([^&]+)=([^&]*)");
    var matches = reg.Matches(query);
    foreach (Match match in matches) {
        dic[match.Groups[1].Value] = Uri.UnescapeDataString(match.Groups[2].Value);
    }
    return dic;
}

Pals

Thanks!! Does it support single item arguments, as metioned by @Arbour 's comment above? Ignores single item arguments, which can sometimes also appear: arg1&arg2&arg3 – Rogan

Answer 6

For .NET Core there is Microsoft.AspNetCore.WebUtilities.QueryHelpers.ParseQuery

var queryString = QueryHelpers.ParseQuery("?param1=value");
var queryParamValue = queryString["param1"];

Code snippet modified from trackjs.com:

South

Answer 7

System.Net.Http ParseQueryString extension method worked for me. I'm using OData query options and trying to parse out some custom parameters.

options.Request.RequestUri.ParseQueryString();

Seems to give me what I need.

Isolated

Answer 8

HttpUtility.ParseQueryString will work as long as you are in a web app or don't mind including a dependency on System.Web. Another way to do this is:

// NameValueCollection nameValueCollection = HttpUtility.ParseQueryString(queryString);

NameValueCollection nameValueCollection = new NameValueCollection();
string[] querySegments = queryString.Split('&');
foreach(string segment in querySegments)
{
   string[] parts = segment.Split('=');
   if (parts.Length > 0)
   {
      string key = parts[0].Trim(new char[] { '?', ' ' });
      string val = parts[1].Trim();

      nameValueCollection.Add(key, val);
   }
}

Renitarenitent