ASP.NET also has UI, Event Handling and if good logic layer is implemented then the BLogic layer too. So that can we say its Model View Control style. Or its not that ?
No. ASP.NET Web Forms is an implementation of Page Controller pattern.
Chapter of Fowler's PoEAA about the Page Controller on Google Books
As a pattern MVC is more concerned with the idea that the controller orachastrates the view and the model.
In Web Forms there is no controller. The View and the code behind (closest thing to a controller) are inherently the same thing, there is no separation of concerns.
Also depending on how you go about it, the model part of the MVC isn't necessarily your business logic. For us its literally a View Model, and contains data relevant to the specific view only. Business logic is handled in autonomous components.
With traditional web forms, I generally see the code behind (which is really part of the UI) having intimate knowledge of either business logic or data base access (and often a mixture of both).
Due to code behind it is hard to get away from this.
In my mind web forms create tightly coupled UI and business logic, and don't provide an easy way to enforce separation of concerns.
I'd say web forms does not adhere to the MVC pattern.
In MVC, all requests are routed to a Controller.
In ASP.NET all requests are routed to a Page. That is a View and not Controller.
ASP.NET better matches with MVP rather than MVC. Reason being, in MVP, a View is supposed to process user inputs/requests and pass it on to appropriate Presenters.
Related
While I'm reading the book "ASP.NET MVC 4" I'm wondering about MVVM. I started googling and cannot find any books about developing web applications using MVVM, so I must be missing a bit of information here.
From what I understand, MVVM is used in web applications on the client side via knockout.js and other frameworks.
If however I was to develop a Windows Phone application, I could use MVVM directly without using MVC.
Does that mean, the concept of MVVM / data binding just does not apply to client-server web applications?
MVVM is really sort of a subpattern. There's not really any "MVVM" web app frameworks out there. They're all MVC and you pretty much just incorporate a view model if you want one.
With ASP.NET MVC, in particular, you just create a class, generally with a name in the form of [Model Name]ViewModel or [Model Name]VM. That class will have only the properties from your model that you'll need to work with and anything extra that doesn't make sense to put on your actual database-backed model, like SelectLists, etc.
In your action, you just pass an instance of this view model to your view instead of your model:
return View(viewModelInstance);
And, of course, make sure your view accepts that:
#model Namespace.To.MyViewModel
The only slightly complicated part is wiring the view model to the model (i.e., getting data to/from the view model/model. You can do this manually by explicitly mapping the properties, or you can use something like AutoMapper.
MVVM is the standard design pattern for WPF/Silverlight development, and should not be confused with MVC for ASP.Net development.
The two may sound similar and share some common parts, but they are two different design patterns.
From what I learned about knockout.js, it was designed to create "data bindings" similar to what you would use in WPF/Silverlight development, which is why the MVVM design pattern applies there.
To quote from another answer of mine regarding the differences between MVVM and MVC
In MVVM, your code classes (ViewModels) are your application, while your Views are just a pretty user-friendly interface that sits on top of the application code and allows users to interact with it. This means the ViewModels have a huge job, because they are your application, and are responsible for everything from application flow to business logic.
With MVC, your Views are your application, while your Controller handles application flow. Application logic is typically found in ViewModels, which are considered part of the M in MVC (sidenote: the M in MVC cannot be considered the same as the M in MVVM because MVC's M layer contains more functionality than MVVM's M layer). A user is given a screen (View), they interact with it then submit something to the Controller, and the Controller decides who does what with the data and returns a new View to the user.
MVC is a one-way data-binding system.
Fill your Model in Controller, then pass it to View.
MVVM is a two-way data-binding one.
Fill your Model, use it in View, when the View state's changes, your Model update automatically.(Vice-versa)
Does that mean, the concept of MVVM / data binding just does not apply to client-server web applications?
No, you can apply the MVVM pattern to client-server web applications.
In fact Asp.Net MVC actually kind of does use this pattern - when the controller creates the view, it can pass in a "view-model". This view-model is often a POCO data object with all the data that a particular view needs, drawn from the model (database). The view uses this data to render the html page.
MVVM on wikipedia says it was introduced by Microsoft with WPF. Specifically, the view binds to properties on the view-model. The view-model then maps this to the database. By this definition then, Asp.Net does not exactly match that. Client-side frameworks like knockout.js and vue.js do support this kind of 2-way binding with view-model properties.
All these patterns are based on the fantastic MV* pattern. It was originally called the MVC design pattern. So this is the exact same pattern as Asp.Net MVC then? Actually, not quite. Controller means something completely different to start with (see MVC on wikipedia). The original MVC controller handles all user input directly not via the view. Second, the original MVC pattern was designed for a desktop app GUI and Asp.Net MVC adapted the pattern for use in a client-server web app. An ASP.Net controller is a collection of http end-points which the client-side html page can hit (eg form-post, page-navigation, ajax).
So there are a lot of M-something-V patterns and the general pattern is often called the MVC design pattern.
There's one more important wrinkle: client-side vs server-side. We've introduced rich client-side javascript frameworks and the fantastic MV* pattern is great here too. So now we could have something like: client-side View-Model-ServerHTTPEndPoints and server-side ServerHTTPEndPoints-ServerModel. The server-endpoints refers to Asp.Net controllers or the equivalent in whatever web framework or programming language you are using. From the server-side point of view, the entire client-side html is the view. The client-side model talks to the server ajax api (http endpoints) to sync data or trigger advanced actions. The ServerModel is normally a database. In knockout/vue, instead of client-side "Model", it would be ViewModel. If you use react/vue with redux/flux then the client-side would be View-ViewModel-Model-ServerHTTPEndPoints where the Model would be the redux/flux Stores. Also, often on the server-side, a service is introduced: ServerHTTPEndPoints-Service-Model. This way unit tests can hit the service directly rather than firing up the entire web server and making HTTP connections.
I have used MVVM in desktop applications and I have a property in my viewmodels named Model where I store a business object as the model. My views have a property named DataContext where the viewmodels are stored before the views are loaded. A view bind its controls to the business object using the path DataContext.Model.BusObjPropertyName. I have a UserInteractionService that register from the start the relationships between views and viewmodels. When a viewmodel needs to show another viewmodel, it calls the method ShowView in the UserInteractionService and pass the viewmodel as parameter. Then the service instantiate the view corresponding to the viewmodel received, set its DataContext property with the viewmodel and show it.
If it is possible to do the bindings to a path like that above in Asp, all this model can be reused either in desktop as in Web applications.
ViewModel is a term that is used in both MVVM (Model-View-ViewModel) and the recommended implementation for ASP.NET MVC. Researching "ViewModel" can be confusing given that each pattern uses the same term.
What are the main differences between the MVC ViewModel and MVVM ViewModel? For example, I believe the MVVM ViewModel is more rich, given the lack of a Controller. Is this true?
A rather challenging question to answer succinctly, but I'll attempt it. (Bear in mind that the answers to these kinds of questions are still the subject of debate amongst developers.)
In MVC, the ViewModel provides all the information necessary for a View to be rendered. The data it contains is created using data defined in the Model. The View reads the ViewModel and renders the output. Input from the View is passed to the Controller, which manipulates the Model, constructs an appropriate ViewModel, and passes this to the View for rendering.
In MVVM, the ViewModel serves the same function as it does in MVC, but it also replaces part of the MVC Controller by providing commands which allow the View to manipulate the Model. WPF databinding manages the updating of the View according to changes in the ViewModel (and this effectively replaces the remaining function of the MVC Controller).
It's been a while since I played UI Design Patterns Bingo.. however let me take a stab at this..
MVVM is just something that MS has come up with... because it helps you to get the most out of WPF. You combine the state and behavior of the view into a class (a presentation model) that is easily testable + then you use data-binding to get the data into any view.
This link has a brief of the evolution of MVVM. Combine this with Fowler's "GUI Architectures" series, and you should be on your way.
Update: Didn't know there was something called MVC-VM. Apparently a brainchild of the ASP.NET MVC crowd. Looks and sounds similar to MVVM (except tuned for ASP.NET MVC); the only difference is that it places a restriction that there is 1:1 mapping between VM and View. I'd have guessed 1:N, but everything else matches.
I know this is a (way) old question, but I've been pointed to it as an example of using "View Model" in the context of MVC. I argue that this is incorrect and can lead to confusion by people who are new to either/or/both patterns. Whoever is doing it--stahp. Here's why (and it's even an answer to the original question in a roundabout way).
An example of when this happens can be seen in this question. The user is trying to use a View Model that implements INotifyPropertyChanged in an ASP.NET MVC application, thus mashing together desktop and stateless web application design in an architectural fail and heartbreak.
To put it simply, there is no "View Model" in the MVC pattern. There is, however, a functional equivalent, and that's the Controller. Just to be clear about the parts and their purpouses,
MVVM (desktop applications):
Model - Strongly typed object that holds data to be passed between the View and View Model
View - The UI viewed by the user and through which the user interacts with the system
View Model - Interprets user actions (e.g., via ICommand), performs them, updates application state
MVC (web applications):
Model - Strongly typed* object that holds data to be passed between the View and View Model
View - A UI generator that combines the Model, code and HTML to render a webpage
Controller - Accepts user requests, interprets them, updates application state and uses a View to convert this state into an HTML webpage
The Model is practically the same in both patterns. Desktop models may implement update event notifications, web Models may be dynamic (i.e., not strongly typed), and both may or may not include validation methods or metadata.
The View in the desktop is what the user sees. In the web, it is a generator that outputs HTML for browsers to display on the client side. It must interpret user interaction on the desktop, but on the web that is handled by client side javascript, the browser, and the requests that are sent back to the server.
The View Model/Controller are roughly functionally equivalent, but differ greatly in how they are implemented and how they operate. In the View Model, user interaction with the application is transferred to View Models via ICommands, routed events, and other methods (many MVVM frameworks provide different ways to hook View Models to the UI and other parts of the application). In a Controller, a request comes in with all information needed for the Controller to return a result to the user (assuming it's a 200 OK request). The Controller must perform whatever work is necessary to create the state (aka Model) needed for the HTML generator (the View) to create the response. Design-wise, the Controller sits above the View and Model knowing and controlling both, whereas the ViewModel sits next to the View, passing the Model (and other information) between them.
What really seems to confuse some people is that there are client side MVVM frameworks that you can mix into your MVC application. These exist solely in javascript in the user's browser, and have nothing to do with whatever particular pattern you're following on the server side. You can run a classic ASP website that uses MVVM on the client side. Hell, you can run static HTML pages that use MVVM on the client side. They are that separate.
These javascript MVVM frameworks typically follow a similar pattern to the desktop MVVM pattern described above, but adjusted to work more in tune with the nature of the HTML DOM and javascript. For example, there is no extensive binding system woven into the DOM, and javascript has a very limited type system, so matching up templates to models is much different than in WPF. They also typically work disconnected from the server, and when they need to interact, prefer AJAX calls rather than POSTing the page back to the Controller (AJAX calls typically are handled by WebAPI Controllers in ASP.NET MVC).
So, to summarize, there really isn't a View Model in MVC. The Controller is the rough equivalent, but is very different in how it receives user input, interprets it, and returns a result to the user. Using the term "View Model" to refer to anything in MVC can only lead to confusion, and therefore should be avoided. Use the proper terms for the proper parts of the pattern. It may seem pedantic, but it should help keep things clear and be less confusing to people who are new to both patterns.
Greetings,
Apologies in advance that I have not researched this toughly enough to answer the question myself, but I imagine it would take me some time and I would rather know now before I invest more time in learning it. I couldn't find anything in my initial research..
Why use ASP.Net MVC if your already using a multi-tier architecture (Data Layer, Logic Layer, Presentation Layer)? Other than the fact the controller has more power than the logic layer.
Am I right in thinking I can use nHibernate and all my data access classes, entities, and mappings in the Model part of the MVC?
When using controllers, is it best to separate a lot of the logic into a separate class so I can call it from multiple controllers? Or can I call them from the controllers themselves, considering the fact that I would not want all of them to be Actions, just normal methods.
Thanks
MVC is not to replace N-Tier, it is a way to organize the presentation layer.
I would not say that the controller is more powerful than the logic layer. Instead, the controller (as a part of the presentation layer) should still call the logic layer.
Controllers should only prepare data for views and handle actions from views. You should still use your BLL.
Yes, NHibernate entities can (and they should be) be passed to the views.
This will you get you into some trouble. You should use flattened, null-safe DTOs a.k.a. view models.
Damien, you might want to read these 2 posts:
The Fat Controller
An Architectural View of the ASP.NET MVC Framework
N-tier is an archtitectual pattern, to enable reuse, seperaation of concerns and scalability of the key areas of your application.
The non UI layers (Business, Data, Facade etc.) should be unit tested and UI agnostic.
The UI layer is just one of these layers weather it be Silverlight, ASP.NET MVC, web forms etc.
MVC, like MVP is a design pattern that enables better testability of the UI Layer.
ASP.Net MVC is an out of the box framework that supports and enforces this pattern.
The pattern was arround an in use long before this framework.
But this is simply a UI layer choice, There should be no interaction with databases, services etc in the controllers, they control the state of the view using the model, Should not control the business logic, peresistence, transactions etc.
To answer your question on why use if you are already going multi-tier is that it makes for more organized and search-engine friendly URL's. Also, it is more of a standard pattern than the other patterns tend to be in ASP.Net. That makes it more developer friendly for those that are already using MVC on other platforms.
I will begin this question by admitting I am very new to MVC. The design pattern makes sense to me at a high level, but now that I'm exploring ASP.NET MVC, some of the architectural pieces are challenging my preconceived notions. Learning is a good thing.
I've been working with Oxite lately as a learning tool written by people at the company that created ASP.NET MVC and thus, an ostensible reference application for ASP.NET MVC.
But today I saw a blog post about Oxite by Rob Conery that says:
One of the things that the Oxite team
decided to do was to separate the
Controllers and Views into another
Project for what I can only assume is
the separation of business logic from
view logic. This can lead to some
confusion since Controllers are meant
to handle application flow - not
necessarily business logic.
This has thrown me for a loop. Is this separation a tenet of MVC and thus a mistake by the Oxite developers, or is it Rob's opinion? If the business logic belongs in the model, why did the Oxite team put it in the controller? How do I execute an action that is business logic if not in the controller?
Further to that, am I making a mistake using Oxite as a learning benchmark considering comments like Rob's?
Your business logic goes in your business layer. The controllers use the business layer to create a model for your views to render. A good example is the MVC Storefront application that Rob Conery has produced. Oxite is currently getting lots of bad press as it apparently does not make good use of the MVC framework.
The reason that you want a business layer that is separate from your controllers is you may want to reuse the business layer across multiple controllers, or even multiple applications. An example of this would be normal user functions for displaying data, and administrative function for updating and adding data. You may make use of the same BL components in both cases but have different controllers and views to render to the data. Model objects would be the same.
You could implement your business layer (i.e. the Model) with your entities, aggregates, repositories, and services. The services call the repositories, which pull data from your DAL in the form of entities.
This can be set in a single, seperate project which is nothing more than a DLL.
Next, have your MVC App, which is really your Presentation layer, and have it utilize your business layer project. the controllers will work with your Services, and pump the data those Services generate into ViewData which is then pumped into your Views.
The controllers should only deal with routing concerns, such as which views to display, based upon user input from forms, querystrings, cookies, sessions, etc.
there has been an uproar from the "MVC purists" community about the validity of Oxite being used an a good MVC example. The bottom line is, business logic should not be contained in controllers, which I am sure you will see as Oxite gets refactored over the coming months.
What are the basic differences between classic .cs-aspx.cs-aspx (code behind/beside) model and new MVC model?
The basic difference between MVC and classic ASP is that in classic ASP all of the code and mark-up for the application exists in the .asp file. In MVC the .aspx file contains only the code and mark-up for rendering the page. The rest of the application for handling requests, retrieving model data, and enforcing business logic exists in controller and model classes. These classes can be much more easily tested than class ASP code because it is separated from the code that is responsible for rendering the view.
This separation of concerns is the basis of the MVC pattern. According to the pattern, the code is divided into three major components -- Model, View, and Controller. Classes in the model represent the business objects for the application, the persistence framework, and business logic applied to the business objects. Classes in the controller accept incoming requests, use the inputs or query parameters to retrieve the appropriate model data, and generate the necessary data for the view to render. Views (aspx pages) take the data supplied by the controller and generate the mark up.
Webforms (codebehind) is somewhere between classic ASP and the MVC pattern. Webforms does not enforce the separation of concerns in the way that MVC does, but it does allow much more of the code to exist "behind" the actual page. For example, you can separate out the business objects, business logic, and persistence framework (the Model, if you will) from the code that is responsible for generating the view. The difficulty is that the controller actions (input handling and model retrieval) are still linked with the view rendering code. This integration makes it much more difficult to test this code and makes the view/controller code much more dependent on each other than is necessary -- the concerns are "mixed", not "separated." In general, this is evidence of bad design because it make it more difficult to make needed changes in the future.
Hope this helps.
Simply put it this way: MVC is how really web apps should be built. Code-behind (asp.net web forms) is not a good practice. If you are truly a developer you will appreciate that the MVC is the best practice since it really separates logic from data and presentation. Simply MVC is the elegant and right way.
A really simple way to perceive the difference between MVC and ASP (or ASP.NET forms for that matter) is that in MVC the Controller is the handler of the request.
Requests get routed to a controller not a 'page' or a 'form'. The controller will pass along info in the request to the model then make some simple choices as to which view that should be used to present the desired state of the model. Note this is the important point the controller has a choice of what view to use in the response.
MVC breaks the relationship between the requested URL and the UI code needed to render a particular representation of data.