In ASP.NET MVC, can I automatically model bind to a JObject from the POST body?

Question

I have a controller action that takes a JSON document as the body of a POST request. I'd love to automatically create a JObject from that, via model binding, like this:

[HttpPost]
public ActionResult Index([FromBody] JObject data)
{
  // "data" is now a populated JObject object
}

But I get errors about not creating an abstract class. I tried to extend something from JObject, but it wouldn't do that either.

I know I can just read the body of the request and call JObject.Parse on it (I'm doing this, so it does work), but my idea from above seems so much more elegant.

Is this possible?

Edit: The actual error is:

System.MissingMethodException: Cannot create an abstract class.
[MissingMethodException: Cannot create an abstract class.]
System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck)
[Stack trace continues...]

The request never gets into the controller action.

Based on my research JObject isn't abstract, but just to be sure, I did this:

public class Entry : JObject

Then

public ActionResult Index([FromBody] Entry data)

Didn't work. Same error.

Answer 1

There might have been two problems. I changed two things, and it works now, but I'm not 100% sure which one fixed it.

Here are both things I changed --

First, I inherited from ApiController instead of just Controller. I'm not sure if this had anything to do with it.

Second, one of the other answers pointed out that I needed to have the correct Content-Type header of application/json. Well, it wasn't. The Content-Type header was set to some wild value specific to the software we're integrating with.

So, in Application_Start, I added this:

GlobalConfiguration.Configuration.Formatters.JsonFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue("[crazy ass content-type header value]"));

And then it worked.

I suspect it was the second thing that fixed it. Since the header didn't tell the model binder it was incoming JSON, the binder was trying to create a JObject object from scratch and assign properties via reflection which ran into problems with JToken being abstract. Once it knew it was dealing with JSON, it knew to just call JObject.Parse instead.

Answer 2

You should also put the structure of the JSON in your question. The full request would be better. Until then, try the following:

replace [FromBody] JObject data with [FromBody] dynamic data or [FromBody] object data

and see if it hits a breakpoint put on the first line of the action.

If it does, see what your dynamic actually is (type).

If it does not, maybe the POST request does not have Content-Type: application/json

Answer 3

The issue is that at some point when deserializing to type JObject, it calls to create a `JToken' and that is where the exception is thrown. Here is the exact exception:

Cannot create an abstract class. Object type Newtonsoft.Json.Linq.JToken

Answer 4

I've written a ASP.NET Core ModelBinder for JToken which you can install - https://github.com/mcintyre321/AspNetCoreJTokenModelBinder

Bind to JToken, then use .ToObject<T>() in your controller