I have read in some places that Smalltalk-80 original MVC is not applicable to web application development because (1) it was made to develop GUI components, not an entire application and (2) because model cannot communicate with view.
(1) is valid, but I do not understand (2). First, Smalltalk-80 MVC does not says that model communicates directly with view, it does so using events. Second, I have an assumption that only controller would be able to alter the model. Then, in a http request, controller layer alters model layer, which raise events which could be observed by view layer. The only diff to controller->model->controller->view (MVP - passive view) is how model notifies the view of its changes. Could someone clarify?
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To which part of the MVC pattern belongs an API? Am I right with the assumption that it belongs to the view?
I'm talking about an application which provides an API to access data from the model.
Then these are conceptually different things. You are offering an API on your server (let's assume REST based); the API here is your server and the software which runs on it. That software may internally be built using an MVC pattern. An API request is handled by a controller, a model, and the response is output by the view. An API request uses all three parts of MVC. "The API" is what your software looks like "from outside".
If you consider the server you are connecting to through the API as a data storage, the API is a layer between the data storage and the controller/view.
In MVC architecture, the model contains a data storage with a service that controller or view can access to obtain the data.
In this case, API is the service, so I would say it is part of the model.
I'm trying to learn web development.
I understand (mostly) the concept of MVC, but I'm confused about why an MVC model is used on the server side...like Spring MVC. Isn't the server side the Model and Services, and then the client side Services, View, and Controller (AngularJS even makes that pattern explicit on the client side)?
I'm really struggling with how the MVC model fits into or facilitates server-side development.
MVC is a pattern used by much more than just web applications. Any app with a UI could use an MVC pattern.
The idea is that you have a View (html, or a window in your OS, or even a report or something), and you have a model that represents the dynamic parts of that view. Then you have a controller that is dedicated to processing input and doing the "business logic" to generate the model and apply it to the view.
So.. for example on the Server you might have this MVC pattern:
A controller receives the HTTP request and processes it.
It builds a model
The model is applied to a view to generate HTML and send it back as a response.
On the client it will be similar (but a bit different in Angular's case):
A controller is used to determine and manipulate the model.
The model is then bound to your view via directives. (Angular is really more of an MVVM pattern, but it's similar enough)
The view is similarly bound to your model via directives. (this is where the MVVM part comes in).
The idea here is that both the model and the view are kept up to date by directives.
The controller just contains "business logic" for manipulating the model.
Clear as mud?
No worries. Just know this: It's just a common pattern. It's not "server specific" or "client specific". It can be used anywhere by anything requiring data to be scrubbed into templated output.
EDIT: More thoughts.
In the case of a Web API that serves up JSON (or even XML) on the server, you're still using MVC in most cases. This is because what you're doing is:
Process the request in a controller.
Build up the model in the controller.
Render the model to a "view", which in this case is a view that serializes it out as JSON.
In the good ol' days of yore, the client side was only a display. The server was responsible for communicating with the model, applying business logic, generating a view, and sending the static, rendered content back to the client (browser).
As the web matured, some of those responsibilities migrated from the server to the client. Now, the server-side is often a thin layer like RESTful API that stores the "official" business logic (rather than convenience logic on the client) and stores the model. But for performance and user experience, the client now stores a copy of the model in its own model layer, communicating with the server and/or local storage as necessary, and having its own controllers and view logic to provide an awesome user experience.
So does MVC still apply on the server? Yes! It's just different. The server often generates the initial view from which the client-side application runs (taking localization or internationalization into account, for instance) and still houses the official model. But more importantly, the "view" in MVC just changed. Instead of the server-side view being HTML, it's now JSON or XML that the client application consumes instead of just renders.
So for functionality's sake, we still use MVC on the server. But for an awesome user experience, we use MVC on the client-side now too.
In a desktop application that uses MVC, what object should be responsible for switching from one view to another? A controller at the next highest level of abstraction?
(Conceptual question not particular to language/platform.)
Yes, that would be correct. You can think of your controller as something of a traffic cop. It handles directing the incoming traffic through the appropriate channels (your business services), and then directs it to its next destination (the view).
I've created an MVP (passive view) framework for development and decided to go for an Application Controller pattern to manage the navigation between views. This is targeted at WinForms, ASP.NET and WPF interfaces.
Although I'm not 100% convinced that these view technologies really swappable, that's my aim at the moment so my MVP framework is quite lightweight.
What I'm struggling to fit in is the concept of a "Business Conversation" that needs state information to be either (a) maintained for the lifetime of the View or, more likely, (b) maintained across several views for the lifetime of a use case (business conversation). I want state management to be part of the framework as I don't want developers to worry about it. All they need to do is to "start" a conversation, "Register" objects and the framework does the rest until the "end" a conversation.
Has anybody got any thoughts (patterns) to how to fit this into MVP? I was thinking it may be part of the Application Controller responsibility (delegating to a Conversation Manager object) as it knows about current state in order to send the user to the next view.... but then I thought it may be up to the Presenter to start and end the conversation so then it comes down the presenters to manage conversations and the objects registered for the that conversation. Unfortunately that means presenters can't be used in different conversations... so that idea doesn't seem right.
As you can see, I don't think there is an easy answer (and I've looked for a while). So anybody else got any thoughts?
The classes needed to support a Business Conversation should reside in a presenter if it only involves the User Interface. Otherwise it should be in the Model and controller from the View to the Presenter to the Model. With information about Business Conversations flowing the other way. I suspect is something that can reside just in the Presenter.
Since all Views have access to the Presenter you then have the ability to structure the objects supporting the conversation so that they can be maintained across several views.
Remember Views are a window into what data resides in your software. They did little other display data and pass user interactions back into the presenter which does the logic.
Is Asp.Net Ajax only used at presentation ( UI ) layer, or also at Business Logic layer?
EDIT - to be more precise, is AJAX API also used at BLL layer?
thanx
AJAX Should Only Apply To Presentation Layer....
You must remember that AJAX allows the client (UI/Browser) to make calls back to the server to do something. At which point your business layer should be invoked to get/retrieve data or do something...
So when it comes to a decision on whether or not to add AJAX functionality to a website, you will most likely do it for some UI/Presentation Layer related desired functionality. And as soon as you do add it, your business layer will be used to serve up the information needed to the client.
The AJAX technologies itself do not necessarily apply to the business layer and I would argue that they should not. The AJAX should simply get you to a place in your code where your front end (UI Code) can work with your business layer code.