Moving from the traditional way of architecting web applications with a Business Layer, Service Layer, Data Access Layer and a Presentation Layer to the MVC design pattern, I find it difficult to understand how it fits in the old model.
It seems to be that the MVC model itself already has done allot of the separation of concerns that is needed and used to be achieved via a layered architecture. Can someone shed some light on this subject please?
As a reference, below is how I understand it, please share your view on this
MVC Views and Controllers along with View Models -are- Presentation Layer
MVC Models - could be - Data Access Layer or Business Layer or even Service Layer
I see the Asp.Net MVC part only as the view (or presentation) part of the whole application.
I struggled too with the problem how to structure the app in a proper way.
Following the Onion Architecture I heard about here (and especially the image found here), my solution looks this way:
Project.Core
Business logic/services implementations, entities, interfaces that must be implemented by the other projects (i.e. "IRepository", "IAuthenticationService",...)
Project.Data
DB connection - in my case NHibernate repositories and entity-mappings go here.
Implements data-interfaces of Project.Core
Project.UI.Web
The Asp.Net MVC ("presentation") project - it wires the whole app together.
Has implementations for Interfaces in Project.Core and wires them (and those from Project.Data) up with some DI framework like Castle Windsor.
Project.UI.Web follows the following conventions:
its models are only(!) viewmodels
the views consume their own viewmodel (one-view-one-viewmodel)
the controllers just need to validate the input, transforms it into domain objects (as the business logic knows exacly nothing about viewmodels) and delegate the real work (business logic) to the business services.
Summary:
If you follow this model it's helpful to focus on Project.Core: that is the real application. It doesn't worry about the real persistence of data nor cares about how does it get presented. It's just about "how-to-do-it". But it's laying out the rules and contracts (interfaces) the other projects must provide implementations for.
I hope this helps you with how to layout an Asp.Net MVC application!
Lg
warappa
As others have said, it doesn't change much. My apps are typically architected as such:
Model Layer (Domain and View Models)
Repository Layer (data access)
Service Layer (sometimes implemented
as WCF services depending on the
app/requirements)
Server side MVC
Layer (Asp.net MVC itself)
Client side MVVM or MVC (via
either Knockout.js, Backbone.js, or
Spine.js)
In the server side MVC layer, my controller methods are very light. They typically call a method on a service layer object to get some data and pass it along to the client as Json data.
Because I'm sending Json back, my views are also very light and sparse. Typically just containing script includes and templates which will be rendered with a client side templating library.
In short: nothing much changes.
I'm only familiar with a few presentation patterns: MVP (Model, View, Presenter, common in windows forms/asp.net), MVC (Model, View, Controller) and MVVM (Model, View, View Model, commonly used in WPF/Silverlight).
Link: http://haacked.com/archive/2008/06/16/everything-you-wanted-to-know-about-mvc-and-mvp-but.aspx
Above link should answer some (if not all) of your questions.
The way I usually write ASP.NET MVC applications is by including at least a Service/Business layer hybrid for CRUD operations (because data access belongs neither on the view model or controller and definitely not in the view!).
Very basic explanation:
If you create a new MVC application you will automatically get a Controllers, Models and Views folder.
Your controllers act like your Business Layer
Models are Data Access/Service layer
and Views are the presentation layer.
See http://www.asp.net/mvc for a fully detailed explanation.
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.
working on asp.net MVC from quite some time now
today stuck on a theoretical problem
going through some sample code on MSDN
I read something like this
public class SomeController()
{
public ActionResult SomeAction(SomeModel model)
{
var dataContext = new SomeDataContext();
//basic CRUD operations on data context
//
}
}
here the database obviously is being accessed through the controller and by theory is incorrect
is there something wrong with this example or my definition of what a model and what a controller is needs to be refreshed
UPDATE:-
or there is a possibility that every where on MSDN Models and ViewModels are considered equal
intro
MVC design pattern is quite old. It was originally defined for Smalltalk-80 applications, when "web" was two guys sending ping between universities. Since then it has evolved quite a lot.
The core principle behind MVC design pattern is Separation of Concerns. The pattern separates presentation from business logic. Presentation layer contains mostly views, controller, templates, viewmodels and presenters (depending on which flavor of MVC-inspired patterns you use), while business logic is ends in the model layer.
The model layer, while not strictly defines in the pattern, in ASP.NET MVC consists of services and all the structures that are used by service (including the Model Objects, better known as domain objects).
regarding the question
It is quite common to see DataContext uses in controllers, when you are looking for basic MVC tutorials. MVC architecture is meant of large scale applications, and in a Hello-World example a fully realized MVC architecture would look like just bloat.
The examples sacrifice code separation for sake of simplicity. The interaction with DataContext is basically storage logic, which is one of tasks that model layer handles. When used in controller, it means that your model layer has begun leaking in the presentation layer, and you end up with "Fat controller, skinny model" problem.
In a real world application the DataContext would be part of structure that deal with persistence within model layer. Probably as part of data mappers, if you opt to write them manually.
regarding "update"
The model (I suppose in this case you meant Domain/Model object) is from completely different application layer then ViewModel.
As the name implies, in MVVM pattern the ViewModels replace the Controllers. ViewModel acquired data from model layer, and then transforms it in such a way that is usable for View.
This pattern is best used (if you are really using MVVM) in situation when you do not have full control over behavior over Views or/and Model layer. For example: if you were hired to build an alternative frontend for SAP or when the view is actually some form of hardware device, which expects specific type of input.
The Models are typically the data classes (representing the database tables). The View Models are typically referred to as classes that have been created in order to use them in the view for presentation purposes.
You wouldn't be able to use the DataContext on a View Model in the above case, but you can use it perfectly fine with the above mentioned Model classes (also called DTO classes).
MVC is a GUI pattern, just like MVP or MVVM, it has nothing to do with data access and persistence. It's true that many simple CRUD applications are not much more that MVC and an underlying database, but in more complex applications MVC would be part of the presentation layer.
The DataContext as an O/RM belongs to the infrastructure layer, not the GUI. In MVC the Model can be understood as ViewModel, yes.
Nevertheless the controller can use the DataContext or any other means to retrieve this model from the underlying data store.
My opinion is it does and it doesn't.
It does separate logic and data from UI, but it still crams it all together into a single point application.
That's why I think it doesn't really, because Controllers are business logic, Views are UI, Models are DAL. These are now just layers within the same app.
But are layers supposed to be the first or the second variety to be actually called layers?
Anyone wants to add their own 2 cents?
The MVC template project is just to get you started - you can easily move the Controllers and/or Models out to separate projects if you want to, and if it makes sense in your application. Remember, that for a small app with maybe three controllers, a couple of extra classes in the Models layer plus an EF or LINQ data model, you really don't have enough files to justify separation into different projects.
I don't think of Controllers as business logic. They are application logic, the glue which ties together the business logic (Model) and the presentation logic (View).
Well, my birthday cake had layers but it was still one big cake... so yes?
Off course it does!
I think both views and controllers contain user interface logic... the business logic should be in the model (which is not only the DAL).
As the model you could use e.g. CSLA objects and add another couple of physical layers as needed (through configuration).
You have to know there's a difference between logical and physical layers (or layers vs tiers)...
There are a lot of interesting articles on lhotka's site regarding this topic!
E.g. this one and this one.
Layers and tiers are interchangeable. In context of an n-tier you'd call it a presentation tier but in context of a layered application you'd call it a presentation layer. But really they are the same thing.
A litmus test of n-tier application and loose coupling would be if you can take each of the tiers and build them as separate projects and deploy them on different machines.
The key differentiator for n-tier applications is Separation of Concerns (SoC) and low coupling. A truly decoupled application might be one where you have a tier that contains nothing but pure HTML. Then another which contains pure Javascript and uses AJAX to update the DOM and communicate with the web service. The web service comprises it's own set of tiers.
The web service has a routing engine that routes the requests to the different controllers. The controllers sanitize and interpret the request, verify authentication and what not and call the appropriate models. the models in turn must return POCO objects or DTOs and return these to the Javascript which injects them into the DOM. The Javascript may modify the objects and send them back to be persisted into the database. Entity Framework 4.0 has good support for just such n-tier scenarios though it does fall a bit short in the SoC department (strongly types views for example) but it's practical for more purposes.
MVC Futures I believe has support for some Inversion of Control (IoC) containers out of the box and currently if you want loose coupling and truly n-tier scenarios you will probably need to use an IoC container of your choosing.
"Tier" usually refers to different physical servers, while "layers" refers to separation of functionality into loosely coupled areas.
That is, a 3-tier web application:
Tier 1) DB Server
Tier 2) Web Server
Tier 3) Client browser
3-layer web application:
Layer 1) UI
Layer 2) Business Logic
Layer 3) Data Access
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.