MVC Controller w/ two arguments of same ViewModel type does not bind correctly - ajax

Question

I have the following controller action:
public JsonResult AcceptChanges(RoomPricing currentData, RoomPricing lastSaveData)
{
...
}
This controller receives JSON encoded objects from my AJAX request:
$.ajax(
{
type: "POST",
url: _controllerURL,
data: JSON.stringify({ currentData: _currentData, lastSaveData: _lastSaveData }),
...
});
The AJAX request data is derived from a form in my partial view, which uses a ViewModel of type RoomPricing. Current and lastSave data are respectively the updated and stale serialized versions of the form. The purpose of these objects is to do form update checks server-side. Server-side because the RoomPricing model includes an enumerable and other junk that would make reliable update checking complex and obnoxious to perform client-side.
Now, when the controller receives the currentData and lastSaveData, it automagically creates the RoomPricing objects, BUT both objects are identical, taking on the values of currentData. To be clear: lastSaveData is created, but only in name, as its contents are identical to that of currentData (and so ignoring the data that was passed by AJAX, which I assume goes into the void).
I expect that this behavior is a side effect of MVC trying to be helpful with Model Binding. Does anyone have a suggestion for getting around this problem? Making a super-ViewModel with two RoomPricing objects to use as the controller argument did not resolve this issue.
Thanks in advance!
Edit: The current and lastSave data comes from the following JQuery code:
var $lastSaveFormData = null;
function AjaxSubmitForm() {
var $lastSaveSerialized = ($lastSaveFormData == null ? null : $lastSaveFormData)
var $form = $('#MyForm');
submitOverrideForm(
$form.serialize(), // currentData
$lastSaveSerialized, // lastSaveData
$form.attr('action'),
);
$lastSaveFormData = $form.serialize();
}
Through the above I'm able to keep a record of all changes since the last save. Although the models are somewhat complex, the size of the data being sent is quite small so I figured I'd compare the data server-side, and here we are. Last thing of note is that I've verified that at this point - JSON.stringify({ currentData: _currentData, lastSaveData: _lastSaveData } - the encoded data is as expected...currentData and lastSaveData are unique if form updates have taken place.
Edit: I just noticed something else. Here is the data being sent to the server as well as the data received server-side just prior to being bound to the model:
_currentData, # AJAX call:
"Book%5B0%5D.Author=1&Book%5B0%5D.Title=100&Book%5B0%5D.IsPaperback=false&Book%5B1%5D.Author=2&Book%5B1%5D.Title=2222&Book%5B1%5D.IsPaperback=false"
_lastSaveData # AJAX call:
"Book%5B0%5D.Author=1&Book%5B0%5D.Title=100&Book%5B0%5D.IsPaperback=false&Book%5B1%5D.Author=2&Book%5B1%5D.Title=77&Book%5B1%5D.IsPaperback=false"
JSON received server-side, just before model binding:
{"currentData": "Book[0].Author: 1,1 Book[0].Title: 100,100
Book[0].IsPaperback: false,false Book[1].Author: 2,2 Book[1].Title:
2222,77 Book[1].IsPaperback: false,false", "lastSaveData":"false"}
Its like MVC is trying to bind the distinct values to a single model, realizes it cant, and drops the 'lastSave' data. Then, when the model hits the controller, it discovers that two models are anticipated, so it uses this model for both. Why is it behaving like this and how can I fix it?

Answer 1

You can add another ViewModel:
public class CurrentAndLastSavedRoomPricingViewModel
{
RoomPricing CurrentData {get;set;}
RoomPricing LastSaveData {get;set;}
}
and get it in controller:
public JsonResult AcceptChanges(CurrentAndLastSavedRoomPricingViewModel data)
{
...
}
passing this model with ajax:
$.ajax(
{
type: "POST",
url: _controllerURL,
data: {data: { currentData: _currentData, lastSaveData: _lastSaveData }},
...
});
Or you can get last saved data on server from database and don't pass it from client.