Json dynamic string list - json

Question

I want to return a list of validation errors from my mvc app to the client side to I can take use of the jquery validation showErrors which takes an object
I can get a list of fields and the the erorr(s) that apply to them in any way that is best suited.
I have tried a few formats already, dictionary and none of these serialise to the correct structure as required by the validation library.
ie.
{"fieldname":"some error for fieldname", "fieldname2": "some error for fieldname2"}
All of my examples seem to serialise into something along the lines of
{"Key": "fieldname", "Value" : "some error for fieldname"}
What is the best way to return my data and how can I get it serialised in the correct way that I need?

Answer 1

I suggest you use Json.NET (it is default JSON serializer for ASP.NET MVC 4 as well) and its JsonWriter:
StringWriter errorsStringWriter = new StringWriter();
JsonWriter errorsJsonWriter = new JsonWriter(jsonStringWriter);
errorsJsonWriter.WriteStartObject();
errorsJsonWriter.WritePropertyName("fieldname");
errorsJsonWriter.WriteValue("some error for fieldname");
errorsJsonWriter.WritePropertyName("fieldname2");
errorsJsonWriter.WriteValue("some error for fieldname2");
...
errorsJsonWriter.WriteEndObject();
errorsJsonWriter.Flush();
You can return JSON generated this way with ContentResult:
return Content(errorsStringWriter.GetStringBuilder().ToString(), "application/json");
UPDATE
Json.NET also supports dynamic JSON through JObject. In that case your code can look like this:
var jsonObject = new JObject();
jsonObject.Add("fieldname", "some error for fieldname");
jsonObject.Add("fieldname2", "some error for fieldname2");
...
Creating ContentResult in this case can look like this:
return Content(jsonObject.ToString(Newtonsoft.Json.Formatting.None), "application/json");