Espo Espo - 2 months ago 31
JSON Question

How can I add a custom root node when serializing an object with JSON.NET?

I have added a custom property to some of my objects like this:

[JsonCustomRoot("status")]
public class StatusDTO
{
public int StatusId { get; set; }
public string Name { get; set; }
public DateTime Created { get; set; }
}


The attribute is very simple:

public class JsonCustomRoot :Attribute
{
public string rootName { get; set; }

public JsonCustomRoot(string rootName)
{
this.rootName = rootName;
}
}


The default output from JSON.NET when serializing an instance of an object is this:

{"StatusId":70,"Name":"Closed","Created":"2012-12-12T11:50:56.6207193Z"}


Now the question is: How can I add a root-node to the JSON with the value of the custom attribute like so:

{status:{"StatusId":70,"Name":"Closed","Created":"2012-12-12T11:50:56.6207193Z"}}


I have found several articles mentioning the IContractResolver interface, but I cannot grasp how to do it. My attempts include this unfinished piece of code:

protected override JsonObjectContract CreateObjectContract(Type objectType)
{
JsonObjectContract contract = base.CreateObjectContract(objectType);

var info = objectType.GetCustomAttributes()
.SingleOrDefault(t => (Type)t.TypeId==typeof(JsonCustomRoot));
if (info != null)
{
var myAttribute = (JsonCustomRoot)info;
// How can i add myAttribute.rootName to the root from here?
// Maybe some other method should be overrided instead?
}

return contract;
}

Answer

Here's a solution specifically for Web API, which I am also using: RootFormatter.cs

I wrote it based on Creating a JSONP Formatter for ASP.NET Web API.

Instead of using a custom attribute I am reusing Title field of JsonObjectAttribute. Here's a usage code:

using Newtonsoft.Json

[JsonObject(Title = "user")]
public class User
{
    public string mail { get; set; }
}

Then, add RootFormatter to your App_Start and register it as follows in WebApiConfig:

GlobalConfiguration.Configuration.Formatters.Insert(0, new RootFormatter());

I was able to get a wrapped response similar to WCF's WebMessageBodyStyle.Wrapped:

{"user":{
  "mail": "foo@example.com"
}}
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