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In the past I have primarily built all my web applications using an N-tier architecture, implementing the BLL and DAL layers. Recently, I have started doing some RoR development as well as looking into ASP.NET MVC.
I understand the differences between the different architectures(as referenced by some other SO posts), but I can't really think of any reasons why I wouldn't choose an MVC model going forward for a new project.
Is there any reasons/times in your experience when an MVC architecture would not be suitable, or any reasons why you would choose a BLL/DAL architecture instead?
I don't think your options are mutually exclusive. You could perfectly use MVC while using BLL/DAL for your model logic.
You can implement the M part of MVC as you prefer, there is no restriction about that. Using BLL and DAL would be a valid option.
For me? the only reason I'd not use MVC is because the application I'm working on was already started in web forms. I'm not a big proponent of scrap/rewrite, but anything new I do is in MVC.
One of the factors could be the statefulness of your web application. If it's a basic web application that gets everything from the server with a few JavaScript hooks such as client side validations, then the Rails type MVC is really great. I am not familiar with MVC on ASP.NET, but I've heard it's similar to that in Rails.
If the web application is really stateful, then a better approach would be to have a dual MVC layer - one on the client side, and the other for the server. The MVC on the server will mostly concern itself with authentication, authorization, churning out data in standard formats, etc. The client side MVC will concern itself with things such as DOM events, user actions, how they affect the application state, and how/when should data be requested/sent to the server.
MVC is just a way to organize code, just as BLL or DAL would do. MVC in Rails basically hides DAL altogether by using a set of conventions. Usually business logic resides in the models itself. However, if your application demands more complex BLL where object interactions can be intricate, then there's no reason why that BLL can't peacefully co-exist with the M in MVC.
I don't use MVC only on really tiny projects consisting of ~1-2 files and ~10-20 lines of code. And they will hardly evolve into something bigger.
But if they will, it will be time to rearchitect them into a MVC ones.
The only drawback we've had is that MVC pushes you toward a html/javascript interface where rich internet applications become more difficult. For example if you want to present the user with a calendar control, you may need to roll your own since you can't drop one on from the toolbox. That said, MVC is great. When we really need RIA applications we use MVVM and Silverlight.
For certain pages, MVC can be a little overkill:
splash pages
landing pages
marketing pages that are going to be thrown away after one use
one-off's
It's easy to get wrapped up creating a beautiful MVC architecture, when a small page, concisely written, can be OK on these situations.
MVC may also be impractical if you're in time trouble, and you need something out REALLY fast. Like your marketing team is out at a conference, they're having trouble, and needs something to show in their booth this second before they lose their biggest customer.
Life above the service tier suggests you should use the MVC pattern in a way that adheres to the SOFEA principles, and watch out for "Front controller" type frameworks disguising behind the MVC acronym.
(or, you can still use them, but at least read the article, understand the differences and choose wisely).
The simple answer is, no.
MVC is all around a better architecture than your old-school n-tier architecture, for many reasons. It's the standard approach in other UI models (e.g. Swing). The only reason it took so long to make it to web applications was because it took the software community, collectively, a little while to get used to the statelessness of the web and to be able to deal with the views and controllers in a way that made sense.
Personally, I would rate it based on the complexity of the target application. MVC (or more structured approaches in general) lend themselves very well to large scale applications where design consistency and segregation of code is a benefit outweighing the cost of supporting the design.
If its a small site, or very few pages/controls, I would avoid sticking to strict design patterns. But that is just my preference.
As one poster said, you also have to consider the state of any existing applications, and your development team skills / experience.
We have already use the MVC for the Windows application,Now we need to convert that thing in the Web application we don't have any problem in any thing. We are using the Web service and every Business Logic is in the Web service.
So you can use the MVC in the web application.
M-Model(Functions and Procedure which communicate with Business logic)
V-View(Design)
C-Controller(Form Logic)
so that is no connection in the DAL,BLL and in MVC.
you can define your Business logic and use in it any where in the MVC.
That's my point of view MVC is very useful for Re-usability i prefer if your application is big then you must use MVC.
I wouldn't use MVC pattern only in the case when I have an existing desktop application built with MVP and I have to convert it to a web environment. That's because I already have written logic for presenter.
In any other case I would use MVC.
You can refer to following
http://blogs.msdn.com/b/webtopics/archive/2009/09/01/asp-net-mvc-what-is-it-and-should-i-use-it.aspx
and http://msdn.microsoft.com/en-us/magazine/dd942833.aspx#id0080017 refer "Undisputable Facts".
I'm studying business layer and need a complete reference which covers issues about "how to manage dependency between business layer and other layers", "how many ways are there to send data between layers" and most important for me "how to group business logic and make business component and talk about possible ways....".
do you know any reference?
EDIT:
I would be delighted if you introduce some e-book for it.
Thank you
the best (in my opinion) approaches to decoupling layers it to use a message passing metaphor. This way communication between the layers is done with messages that are types that contain information only pertinent to the communication. These light weight types are then interpreted by each layer as they see fit.
In essence don't pass things that are not needed. If both layers need a piece of information then there is a high likely hood that some other entity should be brokering access to that information (for example persisted data in db).
I recently stumbled onto this one and found it to be a great read (free ebook in PDF, or read it in MSDN), got the printed version on Amazon shortly after.
Microsoft Patterns & Practices Application Architecture Guide 2.0 -
http://apparchguide.codeplex.com/
EDIT: Here's the section on Business Layers in the MSDN version: http://msdn.microsoft.com/en-us/library/ee658103%28v=PandP.10%29.aspx
I think you should consider reading these books.
(source: infibeam.com)
How about something like
Three-Layered Services Application
(source: microsoft.com)
and
Layered Application
My team is in the process of designing a domain model which will hide various different data sources behind a unified repository abstraction. One of the main drivers for this approach is the very high probability that these data sources will undergo significant change in the near future and we don't want to be re-writing business logic when this happens. One data source will be our membership database which was originally implemented using the default ASP.Net Membership Provider. The membership provider is tied to the System.Web.Security namespace but we have a design guideline requiring that our domain model layer is not dependent upon System.Web (or any other implementation/environment dependency) as it will be consumed in different environments - nor do we want our websites directly communicating with databases.
I am considering what would be a good approach to reconciling the MembershipProvider approach with our abstracted n-tier architecture. My initial feeling is that we could create a "DomainMembershipProvider" which interacts with the domain model and then implement objects in the model which deal with the repository and handle validation/business logic. The repository would then implement data access using our (as-yet undecided) ORM/data access tool.
Are there are any glaring holes in this approach - I haven't worked closely with the MembershipProvider class so may well be missing something. Alternatively, is there an approach that you think will better serve the requirements I described above?
Thanks in advance for your thoughts and advice.
Regards,
Zac
It's been 6 months since the question was asked and no one seems to have been able to provide an answer so I thought I'd explain the solution we eventually chose.
Basically, we have decided not to use any implementation of the MembershipProvider - instead we use our own custom Membership Service sitting atop a repository. It was important for us to maintain the existing aspnet_Membership database so our repository has basically duplicated the built-in SQLMembershipProvider functionality (at least, the aspects we need of it) - initially via Linq-to-SQL but now we're transitioning to NHibernate. The plan is to replace the membership database in a year or so when all of our websites are upgraded to use the new model.
It was possible to use a custom membership provider but in the end it became apparent that it was simpler, more consistent, and more maintainable to use a custom implementation. We are still using the built-in forms authentication functionality for verifying that a user is logged in and for redirecting users who try to access secure areas of our site without first being authenticated - but we have overridden the functionality that is tied to the profile provider.
Ultimately, our feelings on this are that while the membership provider is a powerful and easy-to-use tool within ASP.Net, if it doesn't fit with the wider approach used in your application, it is worth considering an alternative approach.
Interesting, thanks for posting your final solution. I am in a similar situation, but writing a custom Membershipprovider. I don't know where to put the provider because it needs access to the DB as well as System.Web namespace. It seems like it's the one class that violates this whole separation of concerns design.
I've been reading through a couple of questions on here and various articles on MVC and can see how it can even be applied to GUI event intensive applications like a paint app.
Can anyone cite a situation where MVC might be a bad thing and its use ill-advised?
EDIT: I'm specifically talking about GUI applications here!
I tried MVC in my network kernel driver. The patch was rejected.
I think you're looking at it kind of backwards. The point is not to see where you can apply a pattern like MVC, the point is to learn the patterns and recognize when the problem you are trying to solve can naturally be solved by applying the pattern. So if your problem space can be naturally divided into model, view and controller then it is a good candidate for MVC. If you can't easily see which parts of your design fall into the three categories, it may not be the appropriate pattern.
MVC makes sense for web applications.
In web applications, you process some data (on SA: writing questions, adding comments, changing user info), you have state (logged in user), you don't have many different pages, but a lot of different content to fit into those pages. One Question page vs. a million questions.
For making CMS, for example, MVC is useless. You don't have any models, no controllers, just a pages of text with decorations and menus. The problem is no longer processing data - the problem now is serving that text content properly.
Tho, CMS Admin would build on top of MVC just fine, it's just user part that wouldn't.
For web services, you'd better use REST which, I believe, is a distinct paradigm.
WebDAV application wouldn't benefit greatly from MVC, either.
The caveat on Ruby for Web programming is that Rails is better suited for building Web applications. I’ve seen many projects attempt to create a WebDAV server or a content management system CMS with Rails and fail miserably. While you can do a CMS in Rails, there are much more efficient technologies for the task, such as Drupal and Django. In fact, I’d say if you’re looking at a Java Portal development effort, you should evaluate Drupal and Django for the task instead.
Anything where you want to drop in 3rd party components will make it tough to work in the MVC pattern. A good example of this is a CMS.
Each component you get will have their "own" controller objects and you won't be able to share "control" of model -> ui passing.
I don't necessarily know that MVC is ever really a bad idea for a GUI app. But there are alternatives that are arguably better (and also arguably worse depending on whose opinion you're asking). The most common is MVP. See here for an explanation: Everything You Wanted To Know About MVC and MVP But Were Afraid To Ask.
Although I suppose it might be a bad idea to use MVC if you're using a framework or otherwise interacting with software that wasn't designed with MVC in mind.
In other words, it's a lot like comparing programming languages. There's usually not many tasks that one can say that one is better than the other for. It usually boils down to programmer preference, availability of libraries, and the team's experience.
MVC shouldn't be used in applications where performance is critical. I don't know if this still applys with the increase of computing power but one example is a call center application. If you can save .5 seconds per call entering and updating information those savings add up over time. To get the last bit of performance out of your app you should use a desktop app instead of a web app and have it talk directly to the database.
When is it a bad thing? Where ever there is another code-structure that would better fit your project.
There's countless projects where MVC wouldn't "fit", but I don't see how a list of them would be of any benefit..
If MVC fits, use it, if not, use something else..
MVC and ORM are a joke....they are only appropriate when your app is not a database app, or when you want to keep the app database agnostic. If you're using an RDBMS that supports stored procedures, then that's the only way to go. Stored procs are the preferred approach for experienced application developers. MVC and ORM are only promoted by companies trying to sell products or services related to those technologies (e.g. Microsoft trying to sell VS). Stop wasting your time learning Java and C#, focus instead on what really matters, Javascript and SQL.
I am trying to coach some guys on building web applications. They understand and use MVC, but I am interested in other common patterns that you use in building web apps.
So, what patterns have you found to fit nicely into a properly MVC app. Perhaps something for Asynchronous processes, scheduled tasks, dealing with email, etc. What do you wish you knew to look for, or avoid?
Not that it matters for this question, but we are using ASP.NET and Rails for most of our applications.
Once you get into MVC, it can be worthwhile to explore patterns beyond the "Gang of Four" book, and get into Martin Fowler's "Patterns of Enterprise Application Architecture."
The Registry pattern can be useful to make well-known objects available throughout the object hierarchy. Essentially a substitute for using global data.
Many MVC frameworks also employ the Front Controller and the Two-Step View patterns.
The "Model" in MVC is best designed as the Domain Model pattern, although some frameworks (led by Rails) conflate the Model with the ActiveRecord pattern. I often advise that the relationship between a Model and ActiveRecord should be HAS-A, instead of IS-A.
Also read about ModelViewController at the Portland Pattern Repository wiki. There is some good discussion about MVC, object-orientation, and other patterns that complement MVC, such as Observer.
This question is so open that it's hard to give a correct answer. I could tell you that Observer pattern is important in MVC (and for webapplication) and it would be a good answer.About all design pattern that exist are common in big web application. You will require to use some Factory to build complexe object and to access some section require some Facade.
If you want more "tips" or good practice instead of design pattern, I would suggest you to use IoC and the use of good Framework instead of starting from scratch. I can suggest you to explain the benefit of having a good ORM engine to drive you persistance layer faster too (usually can come from the Framework too).
Don't look at it from the aspect of what patterns to use with your development approach, but look at it more as how to apply patterns on a problem-by-problem basis. The architectural decisions made for the project provide just as much indication of what patterns to use as other people's experience will dictate.
That said, I have found that I am a fan of the Provider model for having multiple choices to accomplish a single task with ease of deployment added in. Also, the Unit of Work pattern is great for setting transactional boundaries. Largely, though, the architecture and business needs dictate the approach that is taken for any given code change or new development.
As much as I love patterns, I always fear seeing them overused. I have personally seen people that have used them just for the sake of using them, and it has actually made the code harder to maintain and more tightly coupled than it should have been. Also, it is good to know both sides of the patterns argument. A good pattern knowledge should be rounded out with (often considered a pattern, on its own) anti-pattern knowledge, as well.
I would most likely recommend some kind of Dependency Injection as well (Inversion of Control). Probably the single most important supplementary "pattern" to use.