public class SampleController : ApiController
{
    [HttpGet]
    [Route("api/getobject")]
    public HttpResponseMessage GetByGSTNumber(string token, string key)
    {
        DataConnection connection = null; new DataConnection();//Set up COM reference
        DataObject dataObj = null;
        try
        {
            connection = new DataConnection();
            connection.login(token);
            dataObj = new DataObject(connection);
            Request.CreateResponse(HttpStatusCode.OK, dataObj);
        }
        catch (Exception ex)
        {
            return Request.CreateErrorResponse(HttpStatusCode.InternalServerError, ex);
        }
        finally
        {
            if (connection != null) { Request.RegisterForDispose(connection); }
            if (dataObj != null) { Request.RegisterForDispose(dataObj); }
        }
    }
}

public class DataObject : IDisposable
{
    internal DataConnection dbConnection;
    internal dynamic _dataRecord;
    public string Key
    {
        get { return _dataRecord.KeyField.ToString(); }
    }

    public string Property1
    {
        get { return _dataRecord.Property1Feild.ToString(); }
    }

    public DataObject(DataConnection connection)
    {
        dbConnection = connection;
    }

    public void OpenRecord(string key)
    {
        if (!_dataRecord.Seek(key))
        {
            throw new Exception("Record not found");
        }

    }

    #region IDisposable Support
}

return Request.CreateResponse(HttpStatusCode.OK, dataObj);
//Returns JSON even if specifying XML in request

return Request.CreateResponse(HttpStatusCode.OK, dataObj "application/xml");
// returns <ExceptionMessage>Could not find a formatter matching the media type 'application/xml' that can write an instance of 'DataObject'.</ExceptionMessage>