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
Related
I'm about a month into MVC and from what I understand, a pretty good approach to app architecture is:
MVC <> Service <> Repository <> Core
Within MVC we have Views, and Controllers to populate viewModels for the controllers. My question is: Where exactly to Data Transfer Objects come in? I'm building a single-page web app and I'm trying to do it right from the beginning.
From the reading I've done, I should use DTOs to "flatten" the Model objects before passing them into the ViewModel. Do they act as a "only data that I need" object that gets passed from the service to the controller, at which point the viewModels are constructed? If so, is it generally true that each model definition (ie Sets, Cards, Users) should have corresponding DTO classes in the Core layer? Any clarifications here would be awesome, thank you for your time!
First of all, about this phrase: "a pretty good approach to app architecture is...": I don't believe there is a single good approach to all apps, and I would prefer always to use the simplest approach (i.e. fewer layers) that could solve your problem at hand.
When you say "Service", it appears to be a whole layer of web services, rather than just some domain service classes; in most cases I've seen with Asp.Net MVC, the controller itself can fulfill the role of a service, thus eliminating the need to add yet another layer. Of course there are exceptions, just be sure your reason to increase complexity is legitimate.
About DTO's and View models: DTO's, like you described, flatten the object model and return "only data that I need". DTO is a more generic term, usually used with web services where you don't know who is the consumer. Think of (Asp.Net MVC) View Models as a more specialized kind of DTO, that returns "only data that THE VIEW needs". Thus, if you don't need an extra layer of services, you also don't need an extra layer of DTO's, just use View Models to flatten the domain classes directly and return them from your controllers.
In fact, for very simple applications, even the separation of Models x ViewModels is overkill - it is possible to use a single Model layer to fulfill both roles, with the help of the ViewBag. I don't know your requirements, so I can't say which is better for you.
Finally, one comment: if you must build a single page application, Asp.Net MVC is not the best tool for the job. I'd recommend using Asp.Net Web Api (only services, no views) at the server and a client mvc framework, such as BackboneJs or AngularJs.
I know this has been sort of answered in various posts, but using VS2012 with MVC4, I wonder if there is a more updated method or new ways to do things.
I have a large enterprise application that has 22 projects in it. It has a complex large business object/logic project and has multiple presentation layers. Working on a new presentation layer using MVC 4. I have never used MVC before at this scale.
Here are my questions:
How do people handle the model in this scenario? All the Microsoft examples are so simple.
I have seen posts to auto mappers and recommend deves use simple models and extract from the BO layer, but some of these tools like auto mapper seem to have gone idle, is there a library in MVC that does that now?
I'm just trying to figure out best practices before I get started, seems usually I figure them out after the fact.
I break my MVC apps into several different projects.
AppName.Configuration: to handle any configuration of the app (i.e. pulling in web.config/app settings, etc)
AppName.Data: this is the data layer where all DB access is performed (no business logic). The DBML/EDMX lives here, my repository class(es) live here as well.
AppName.Models: this is where all of my ViewModels are defined for MVC, as well as other model objects needed throughout the application.
AppName.Services: This is my business layer, all everything must pass through here to get to the data layer or to the presentation layer. ViewModels are constructed from the database objects, data validation happens here, etc.
AppName.Web: this would be the MVC application.
AppName.Data.Test: Unit tests for Data app
AppName.Services.Test: Unit tests for the services
AppName.Web.Test: Unit tests for the MVC controllers
AppName.Web.UI.Test: Unit tests for the web user interfaces (using WATIN)
I don't use any auto-mappers, as i clearly define a specific viewmodel for each view of the application. If it isn't needed for the view, it doesn't go in there.
Most MVC examples are so basic, they show everything in the web app (data, models, business logic in the controllers, etc.)
I hope this helps.
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I have been developing enterprise applications for many years using .Net
My apps usually have a domain model containing entities mapping to SQL DB tables.
I use a Repository pattern, Dependency injection and a service layer.
Recently we started working on MVC 3 projects and we had a debate where to put which logic.
I came accross thin Controller / FAT Model architecture and was wondering how the service layer would fit in
Option 1 - Model talks to services
Controller is thin, calls methods on the models. The models "know" how to load themselfs from the DB and talk to repositories or services.
E.g. customerModel has a Load(id) method and loads the customer and some child objects like GetContracts().
Option 2 - Controller talks to services
Controller asks Services to retrieve model objects. The logic of loading / storing etc. Is in the service layer. The model is a pure entity model with data only.
Why would option 1 be a better choice especially when we talk about enterprise applictions my experience tells me to separate concerns, keep models AND Controllers as thin as possible and have specialized services doing the Business logic (imcl. The DB interaction)
Thanks for all advices and references to good resources.
All of this depends on the intention and requirements of your application.
That said, here's my suggestion for "mid scale" (not a local restaurant, and not Twitter/Facebook) web applications.
Lean Domain Modeling
Dry POCO style objects, preferably ignorant to the MVC architecture of your web application to remain as loosely coupled from your particular implementation as possible.perhaps even class library repack-able for use in an external application, say a REST API via a WCF Web Service).
"Model" in MVC most accurately means the model the Controller is aware of and thus the the model intended for the View.
In smaller (often Tutorial) applications the entity models of your "Application/Domain Model Layer" are often the same instantiated objects the controller ships off to a View.
In larger applications developers often employ the tenets of MVVM architecture and begin using separate View Model objects. The controllers often call middle-tier services that work with the unseen entities below. In this scenario, the M in MVC most accurately means the View Model.
Robust Service Layer
This does not mean obese logic, but well-written single purpose services. While coding your business logic in services outside of the model is a bit more "procedural" than it is pure "OOP", it helps a lot with loose coupling, testing, and flexible deployment (ex. n-tier deployment).
In my personal practice, I code services both down at the data layer, which I consider my behavioral modeling of the POCO objects (persistence mechanics, low level validation, etc.), and higher level services (business/workflow function) up closer to the MVC mechanics.
Lean Controllers
I make sure my controller is merely the coach, in that it is neither the play (services) or the player (entity model or view model), but simply decides who plays what position and what play to make. My controllers do two things:
Call services that interact with the entity/domain Models
Prepare a View Model for the appropriate View.
Even authenticated/authorized controller actions are done via injected services/attributes.
EDIT 1:
Keep in mind, that this does not mean your Entity/Domain Model is or must be anemic. ORMs, repositories and factories, validation or state mechanics are welcome. It only means for applications of moderate scale, the Model in MVC represents the model meant for the controller, to hand off to your View.
Hopefully this point will calm Fowler apostles who believe the anemic data model to be an anti-pattern. At the same time, it does reflect a slightly more procedural angle than OOP where it is more pure to include behavior in the modeled classes.
There is no "ultimate truth", but using this pattern you'll find it easy to build, test, and deploy your applications - while maintaining a lot of re-usability and scalability.
EDIT 2:
That said, even for modestly sized applications, over architecting (that a word nerds made up?) a system is much too common. For instance, wrapping an ORM with a repository pattern, and then writing services to use the repository... all this is good for separation of concern and such, but if your project doesn't require (and is not very likely to soon require) such things, don't build it. There is nothing wrong with skipping the repository all together, writing thin business services (ex. query classes) against an ORM, or even having your controller talk directly to it. It all depends on scale.
EDIT 3:
I wanted to note that this explanation and advice is for the context of server-side MVC architecture like ASP.Net, not for clent-side frameworks like Knockout or Backbone.
You need to know some more about MVC before we go ahead and discuss where to put everything. Well, if you want to follow the pattern. Otherwise you can stop reading now.
The pattern is very loosely defined. There is nothing that says how the controller, view or model should look like or how they should be structured. The pattern simply states that you should separate the parts and how they should interact with each other. So let's look at bit more about what they are (my interpretation).
MVC
Model
The model can be anything. It can be a webservice, your repositories, your service classes or simply your domain models. The Model are everything that are used to get the information that you need. Consider the "Model" as a layer instead of just an single object.
Controller
The controller is a glue. It takes the information from the Model and adapts it to the view and vice versa.
View
The view should only render what the user sees.
Do note that you should not confuse the Model with View Models. Microsoft should really have named the "Model" folder "ViewModels" since that's what they are. I would not use information from the "Model" directly in the views. Failure to do so would mean that you have to change the Model if the View is changed and the other way around.
The answer
The model is not a view model but a layer. Everything in the model is used to fetch the information needed for the view. The controller takes that information and puts it into a single view model.
A single controller action might use one or several calls to the "Model" to be able to assemble the information needed by the view.
That means that your second option is the most correct when if you want to get an application which is easy to maintain and extend.
Do note that a service layer might not be needed. You can call the OR/M directly from the controllers. But if you find yourself duplicating code or getting fat controllers, simply move the logic to a service layer. Nothing but the controller will be affected by that change since you are using proper view models.
Option 1:
You could think that model == service.
Model also IS the business layer.
Option 2 is an Anemic Domain Model anti-pattern.
http://en.wikipedia.org/wiki/Anemic_domain_model
Option 2 is what's described as Fat Stupid Ugly Controllers architecture (Reference to author of this expression). This solution is generally against MVC spirit as it breaks separation of concerns.
I'm looking for some feedback on my ASP.NET MVC based CMS application architecture.
Domain Model - depends on nothing but the System classes to define types. For now, mostly anemic.
Repository Layer - abstracted data access, only called by the services layer
Services Layer - performs business logic on domain models. Exposes view models to the controllers.
ViewModelMapper - service that translates back and forth between view models and domain models
Controllers - super thin "traffic cop" style functionality that interacts with the service layer and only talks in terms of view models, never domain models
My domain model is mostly used as data transfer (DTO) objects and has minimal logic at the moment. I'm finding this is nice because it depends on nothing (not even classes in the services layer).
The services layer is a bit tricky... I only want the controllers to have access to viewmodels for ease of GUI programming. However, some of the services need to talk to each other. For example, I have an eventing service that notifies other listener services when content is tagged, when blog posts are created, etc. Currently, the methods that take domain models as inputs or return them are marked internal so they can't be used by the controllers.
Sounds like overkill? Not enough abstraction? I'm mainly doing this as a learning exercise in being strict about architecture, not for an actual product, so please no feedback along the lines of "right depends on what you want to do".
thanks!
Overall, the design looks good to me.
There are a few more items I might do:
Validations - have a 2 step validation -
Step 1 : the domain-level classes enforce their own validity (via attributes or any other mechanism).
Step 2: The repository ensures that the object is valid in the context of the repository
Dependency Injection - use a DI framework to inject dependencies. It will be useful for unit testing. Also, If the service layer where you need to call across services, check if this article on Aggregate Service is useful: http://blog.ploeh.dk/2010/02/02/RefactoringToAggregateServices.aspx
ViewModels - might be tempting to re-use, but wait & watch before you finally decide
HTH.
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.