x-www-form-urlencoded content is, essentially, a flat sequence of key/value tuples, and as explained in this answer to How do I use FormUrlEncodedContent for complex data types? by Tomalak, there is no canonical way to transform a hierarchical, nested key/value structure into a flat one.
Nevertheless, from the accepted answer to this question, this example from the Stripe API, and the question mentioned above, it seems that it is common to flatten parameters inside complex nested objects by surrounding their keys in brackets and appending them to the topmost key like so:
{
{ "purchase_invoice[date]", "14/04/2015" }
{ "purchase_invoice[due_date]", "14/04/2015" }
{ "purchase_invoice[contact_id]", "500" }
{ "purchase_invoice[contact_name]", "TestContact" }
{ "purchase_invoice[reference]", "TestReference" }
{ "purchase_invoice[line_items_attributes][0][unit_price]", "10" }
{ "purchase_invoice[line_items_attributes][0][quantity]", "1" }
{ "purchase_invoice[line_items_attributes][0][description]", "TestLineItemAttDesc" }
{ "purchase_invoice[line_items_attributes][0][tax_code_id]", "1" }
{ "purchase_invoice[line_items_attributes][0][ledger_account_id]", "501" }
{ "purchase_invoice[line_items_attributes][0][tax_rate_percentage]", "19" }
{ "purchase_invoice[line_items_attributes][0][tax_amount]", "1.6" }
}
If this is what you want, you can generate such key/value pairs with json.net using the following extension methods:
public static partial class JsonExtensions
{
public static string ToUrlEncodedQueryString(this JContainer container)
{
return container.ToQueryStringKeyValuePairs().ToUrlEncodedQueryString();
}
public static IEnumerable<KeyValuePair<string, string>> ToQueryStringKeyValuePairs(this JContainer container)
{
return container.Descendants()
.OfType<JValue>()
.Select(v => new KeyValuePair<string, string>(v.ToQueryStringParameterName(), (string)v));
}
public static string ToUrlEncodedQueryString(this IEnumerable<KeyValuePair<string, string>> pairs)
{
return string.Join("&", pairs.Select(p => HttpUtility.UrlEncode(p.Key) + "=" + HttpUtility.UrlEncode(p.Value)));
//The following works but it seems heavy to construct and await a task just to built a string:
//return new System.Net.Http.FormUrlEncodedContent(pairs).ReadAsStringAsync().Result;
//The following works and eliminates allocation of one intermediate string per pair, but requires more code:
//return pairs.Aggregate(new StringBuilder(), (sb, p) => (sb.Length > 0 ? sb.Append("&") : sb).Append(HttpUtility.UrlEncode(p.Key)).Append("=").Append(HttpUtility.UrlEncode(p.Value))).ToString();
//Answers from https://stackoverflow.com/questions/3865975/namevaluecollection-to-url-query that use HttpUtility.ParseQueryString() are wrong because that class doesn't correctly escape the keys names.
}
public static string ToQueryStringParameterName(this JToken token)
{
// Loosely modeled on JToken.Path
// https://github.com/JamesNK/Newtonsoft.Json/blob/master/Src/Newtonsoft.Json/Linq/JToken.cs#L184
// By https://github.com/JamesNK
if (token == null || token.Parent == null)
return string.Empty;
var positions = new List<string>();
for (JToken previous = null, current = token; current != null; previous = current, current = current.Parent)
{
switch (current)
{
case JProperty property:
positions.Add(property.Name);
break;
case JArray array:
case JConstructor constructor:
if (previous != null)
positions.Add(((IList<JToken>)current).IndexOf(previous).ToString(CultureInfo.InvariantCulture)); // Don't localize the indices!
break;
}
}
var sb = new StringBuilder();
for (var i = positions.Count - 1; i >= 0; i--)
{
var name = positions[i];
// TODO: decide what should happen if the name contains the characters `[` or `]`.
if (sb.Length == 0)
sb.Append(name);
else
sb.Append('[').Append(name).Append(']');
}
return sb.ToString();
}
}
Then if you have a JSON string, you can parse it into a LINQ-to-JSON JObject and generate the query string like so:
var obj = JObject.Parse(jsonString);
var queryString = obj.ToUrlEncodedQueryString();
Alternatively, if you have some hierarchical data model POCO, you can generate your JObject from the model using JObject.FromObject():
var obj = JObject.FromObject(myModel);
var queryString = obj.ToUrlEncodedQueryString();
Demo fiddle here.
