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I'm playing around with ASP.NET MVC 4, but I have some problems with understanding. For better explanation I will use a simple "synthetic" situation. Let's say I have model Person with 2 properties:

  • string Name
  • PersonType Type (e.g. Student, Employee, Military...)

Let's say in my controller I have private property Person. I can initialize this object in Index method, pass into View and build html page. Ok.

Now when user updates one of fields of person instance at the client side (he can input a new person name or select new person type using dropdown list), I want to update my model immediately. So, my general question is How can I achieve it?

Obvious solution for me: I can send an ajax request to controller from JS with new data. I thought that I can call controller's method UpdateName(string name) and update manually property Name with new data. BUT my person instance is NULL inside of this method! My second question is Why I can't access to initilized model object from other method? I think it's all about my bad understanding of client server interaction.

The final case of my situation: when user click's on the button "Save" I want to save created person into file on the server side, but I don't want to use any forms and receive all needed data just after clicking this button (because in my real task I can't use forms and also I can't receive all needed fields from html page after button clicking).

I have found the dirty solution. In JS I created another class Person with same properties. Now I can update instance of this class when I want and pass json data to server for saving it.

Is there any better solutions?

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Its not that dirty to have javascript objects to represent your model. In fact thats how I do it. I use KnockoutJS to give me a client side model - which is essentially the MVVM pattern.

You are trying to use the MVC model in a way which you can't. However, the Knockout model you can use how you wish. You basically have a javascript representation of your server side model and once you are done with it you send it to the server.

In order for your server side methods to pick up your client side model you simply have to ensure the post request contains the data and as long as properties names are the same in the parameters of the method they will match themselves.

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Why I can't access to initilized model object from other method?

Because it's not initialized anymore. Don't use the controller class to store persistent data across requests. The controller object is disposed after a request completes and then re-initialized on a new request. So anything that one action methods saves at the class level is gone when you get to another action method. Each request from the client to the server should be considered a fully isolated event, independent of any previous requests.

When you want to save your model, what you would do in that action is re-fetch it from the database, apply the changes, and save it back to the database.

but I don't want to use any forms

I'm not really sure what you mean here. Do you mean you want to use AJAX instead of POSTing the page directly? If so, that's fine. There are probably a number of tools out there to help you, personally I often just create a form anyway but instead of a submit button I have a plain button and add some JavaScript code (using jQuery) to serialize the form and perform an AJAX POST.

As long as the keys for the POST values map to your model fields in the same way they would in an out-of-the-box form, then your action method will still be able to receive the proper model type. On the server-side it doesn't matter if it's from an AJAX call or a normal POST. The difference, however, is that the response for an AJAX call should probably be in JSON format instead of responding with a view.

So instead of this:

return View(someModel);

You might have something like this:

return Json(someModel);
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David, thank you for really helpful explanation! By "I don't want to use any forms" I mean that in my real project I can't collect all needed fields from page by clicking on button. I'm using dynamically loaded partial views and some fields can be removed from the page by the time of button clicking. So, should I use a JavaScript ViewModel for have always up-to-date data?

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