I have an established web application built as an ASP.NET 3.5 Web App. We recently modified it to mix MVC into the app for some new functionality.
Now that it's in there, we want to leverage MVC wherever possible to begin to "transform" the app from clunky webforms to a more maintainable and testable MVC app.
The question that just came up in adding some new functionality is what controller should be responsible for a certain action.
Let me be more detailed.
The scenario involves at least three major conceptual areas in our app. The app needs to be able to set their PREFERENCE for a default MAP view while they are on a SEARCH screen. Preferences, Maps and Search are all major concepts in our system. Furthermore, this preference setting (basically, where should the map start out) may be used to set the initial map in more than one search page (it's basically a search preference).
The existing MVC controller in the app is a MAPCONTROLLER, with 3 actions that are responsible for generating HTML or JSON data to put on a map.
What we need to do now, is add an MVC route (controller + action) to allow the client view to save some information as their preference. Basically, whenever they are on the search page looking at a map, they can click a button that says "remember this as my default map view", and from then on, their map will always start with that view.
My question is (and I apologize, but I wanted to be very very clear, I see too many questions with no context to help). What should my controller represent? I obviously have 3 major system areas involved. Would it be proper to create a new SEARCH or PREFERENCES controller with a SaveDefaultMapView action (no view required), or piggyback on the xisting MAP controller, even though this new function is more about search and preferences than actual map generation? Should an MVC controller be aligned mostly with the screen (search page/search subsystem), the domain / data being manipulated (preferences), or the very specific visual element under scrutiny at the time the action is taken (the map)?
All of the examples and bootcamp projects are all well and good, but they are far too clean and simplified to apply to a huge legacy app. How does one design their MVC components around a system that incorporates many domain concerns into a single webpage?
Thanks all!
There are no hard and fast rules for how the controllers are organized. You organize them the way it makes most logical sense to you. This will require a bit of experimentation as you see how the routing works out, and you find the cleanest, most elegant design.
ASP.NET MVC is brilliantly agnostic in this respect. It doesn't care how you design your controller/route substructure, and it is flexible enough to handle most any design.
Your application design should be heavy on the Model side. Your controllers should be relatively small; if you find that you are stuffing a large amount of logic in the controllers, you should refactor that logic to the model, or add a service layer to contain the logic. Your controller layer is best thought of as a "patch panel"; it is the place where you connect your incoming Urls via routes to your model/service layer and your View Model/Views.
You should definitely check out Project Areas, as this might be an appropriate mechanism to contain your three different system areas.
Thanks, Robert.
I guess I could rephrase a bit...what guidelines have others found to be useful for keeping their controller responsibilities organized and logical?
While my example above only touches 3 of our areas, I expect to eventually replace most/all of the application with MVC.
Furthermore, each of the 3 areas I mentioned has relationships to multiple other areas.(eg, maps can be used to plot several location-based entities, preferences can apply to any area of the system, and, like maps, is capable of searching for several kinds of business entities (one at a time, not all together).
So the lines are blurry. I'm interested in hearing how others have found workable guidelines for controller organization.
Oh, and at the very least, we are sticking to the skinny controller/fat model paradigm!
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I've done some surface reading on mvc and mvp and they all talk about model, controllers and presenters. My looking up on those things didnt give me enough understanding so I want to know how important using an mvc or mvp is to website development, if it is compulsory to use either of them and lastly their benefits.
It is not like you can't develop web applications without the use of either of MVC or MVP. But they both are designing patterns and helps greatly in development an maintenance of your project and code.
At the heart of MVC is Separated Presentation. The idea behind Separated Presentation is to make a clear division between domain objects that model our perception of the real world, and presentation objects that are the GUI elements we see on the screen. Domain objects should be completely self contained and work without reference to the presentation, they should also be able to support multiple presentations, possibly simultaneously.
There are mainly 3 design patterns:
MVC (Model View Controller)
MVP (Model View Patterns)
MVVM (Model View View Model)
MVC (Model View Controller)
The MVC pattern is a UI presentation pattern that focuses on separating the UI (View) from its business layer (Model). The pattern separates responsibilities across three components: the view is responsible for rending UI elements, the controller is responsible for responding to UI actions, and the model is responsible for business behaviors and state management. In most implementation all three components can directly interact with each other and in some implementations the controller is responsible for determining which view to display.
Model View Presenter(MVP)
The MVP pattern is a UI presentation pattern based on the concepts of the MVC pattern. The pattern separates responsibilities across four components: the view is responsible for rending UI elements, the view interface is used to loosely couple the presenter from its view, the presenter is responsible for interacting between the view/model, and the model is responsible for business behaviors and state management. In some implementations the presenter interacts with a service (controller) layer to retrieve/persist the model. The view interface and service layer are commonly used to make writing unit tests for the presenter and the model easier.
Key Benefits
Before using any pattern a developers needs to consider the pros and cons of using it. There are a number of key benefits to using either the MVC or MVP pattern (See list below). But, there also a few draw backs to consider. The biggest drawbacks are additional complexity and learning curve. While the patterns may not be appropriate for simple solutions; advance solutions can greatly benefit from using the pattern. I’m my experience a have seen a few solutions eliminate a large amount of complexity but being re-factored to use either pattern.
Loose coupling – The presenter/controller are an intermediary between the UI code and the model. This allows the view and the model to evolve independently of each other.
Clear separation of concerns/responsibility
UI (Form or Page) – Responsible for rending UI elements
Presenter/controller – Responsible for reacting to UI events and interacts with the model
Model – Responsible for business behaviors and state management
Test Driven – By isolating each major component (UI, Presenter/controller, and model) it is easier to write unit tests. This is especially true when using the MVP pattern which only interacts with the view using an interface.
Code Reuse – By using a separation of concerns/responsible design approach you will increase code reuse. This is especially true when using a full blown domain model and keeping all the business/state management logic where it belongs.
Hide Data Access – Using these patterns forces you to put the data access code where it belongs in a data access layer. There a number of other patterns that typical works with the MVP/MVC pattern for data access. Two of the most common ones are repository and unit of work. (See Martin Fowler – Patterns of Enterprise Application Architecture for more details)
Flexibility/Adaptable – By isolating most of your code into the presenter/controller and model components your code base is more adaptable to change. For example consider how much UI and data access technologies have changed over the years and the number of choices we have available today. A properly design solution using MVC or MVP can support multi UI and data access technologies at the same time.
Key Differences
So what really are the differences between the MVC and MVP pattern. Actually there are not a whole lot of differences between them. Both patterns focus on separating responsibility across multi components and promote loosely coupling the UI (View) from the business layer (Model). The major differences are how the pattern is implemented and in some advanced scenarios you need both presenters and controllers.
Here are the key differences between the patterns:
MVP Pattern
View is more loosely coupled to the model. The presenter is responsible for binding the model to the view.
Easier to unit test because interaction with the view is through an interface
Usually view to presenter map one to one. Complex views may have multi presenters.
MVC Pattern
ontroller are based on behaviors and can be shared across views
Can be responsible for determining which view to display
Further More Research on topic to choose best pattern
Further research and also using the term "twisting the triad" will result in a couple of interesting articles to read that always addresses your question.
The most often heard result is this:
Do you develop a web application? Learn about MVC.
Do you develop a winform application? Learn about MVP.
Do you develop a WPF application? Learn about MVVM.
You can follow it on MVC, MVP and MVM Architectures for web development
You're definitely not required to use an MVC or MVP framework when writing a web app. People still write apps using nothing more than jQuery. However, many popular frameworks like angular 1, backbone, and knockout do make use of models, views, and/or controllers or some subset of them so it's probably good to know.
As for the benefits, it comes down to maintainability. As applications grow larger they become difficult to modify successfully without some sort of overarching structure to keep things consistent and to ensure good practices are used. Frameworks like angular provide you with this out of the box by using proven and well understood concepts like MVC. Without this you'll eventually have to come up with your own patterns and subsystems, which while doable, can take a lot of time and effort. Either that, or your app buckles under its own weight.
If you're new to development it's difficult to get an appreciation for this without working on a large project and seeing how crazy things get without some structure. I'm not sure it's something you can learn in a vacuum or that you need to concern yourself with too much right now. Eventually it will become painfully obvious to you why it's important.
As mentioned above, it has a lot to do with the ease of maintaining the code as it grows but that's not all.
A framework such as AngularJS allows you to change the way you build sites by applying the MVC methodology. When working with AngularJS is important to shift paradigms from manipulating the DOM to describing the desired effect and watching it happen.
With MVC each component is kept separate which makes testing them a lot easier. The separation and modular nature of this patterns allows for greater flexibility and allows bigger apps to grow at a faster rate without loosing quality.
A great tutorial on AngularJS can be found at : https://m.youtube.com/playlist?list=PLYxzS__5yYQmX2bItSRCqwiQZn5dIL1gt
Today I was getting some refresh about software design patterns.
In particular I was wondering about the difference between MVC and Three-tier-layer. Basically, from what I read on wikipedia and other sources, the main difference between the two is the components interaction:
A fundamental rule in a three tier architecture is the client tier
never communicates directly with the data tier;
whilst
...the MVC architecture is triangular: the view sends updates to
the controller, the controller updates the model, and the view gets
updated directly from the model
Now: if we take the apple docs regarding this matter we see this:
And they clearify that Views and Model shouldn't communicate directly:
view objects are typically decoupled from model objects in an MVC
application
and
When a model object changes (for example, new data is received over a
network connection), it notifies a controller object, which updates
the appropriate view objects
And so on.
So, what's the matter here? Is Cocoa adopting its own idea of an MVC, regardless of the common one? Or am I missing something in the common way of seeing an MVC architecture?
While it can be said that Cocoa's version of MVC is a sort of subset of the actual definition of MVC, they are not separate entities. The Cocoa version of MVC typically revolves around the use of a View (typically an NSWindow and/or an NSView), a controller (typically an NSWindowController), and a model layer (anything from a simple array to a Core Data stack). The separation of powers in this model is clear, but where in the 'tier' structure that Wiki defines should each of these belong?
I would argue that the Controller and the View are a part of the client layer. Not only is the controller responsible for the delegation between the model and the view, but it is responsible for responding to user events and determining the correct course of action to take during non-framework error handling. By taking this approach to MVC, you can now begin to see how Cocoa does, in fact, satisfy the broader definition of the pattern.
A fundamental rule in a three tier architecture is the client tier never communicates directly with the data tier;
This one's probably the hardest to reason about of the 3, and it involves delving into what "communication" actually means in the context of the pattern. When we say communication, what we mean is that the controller has no direct involvement in the actions taken by the model. That's not to say that the controller cannot order a change in the contents of the model, but rather that the controller does not have a hand in how the model updates itself. The controller acts as a director, not an implementer, which vastly simplifies the creation of a database layer, and is one of the reasons that Core Data and SQLite3 exist as external frameworks rather than as Foundation classes.
view objects are typically decoupled from model objects in an MVC application
That brings up one of the age-old taboos when programming with the pattern: making your views too smart. The controller provides a solid barrier between the model and view, such that the controller acts as a director and a filter for content from the model layer. Without any such barrer, say a tableview, would have to ensure that every cell had a copy of the data from the database, and that each cell knew when and how to update itself when a change is propagated in another cell. In Cocoa, this is where our NSWindowControllers come in. They manage the display of a root view and act as a barrier between some model and the content of the view it manages. Though, it is important to note that the controller objects in Cocoa are view-biased, mostly because it would be nearly impossible to provide a generic outlet to any kind of model layer without quite a bit of unnecessary glue.
When a model object changes (for example, new data is received over a network connection), it notifies a controller object, which updates the appropriate view objects.
That's the way it should be, for the reasons I've laid out above. But, to build on the networking example you've given, consider this:
Given an NSOperation that fetches data, and a controller that manages a tableview, you would probably not like the controller sticking its fat fingers into the operation, nor would you like the tableview to receive raw NSData and have to spend valuable rendering time processing the result and displaying it.
And so on. So, what's the matter here? Is Cocoa adopting its own idea of an MVC, regardless of the common one? Or am I missing something in the common way of seeing an MVC architecture?
I guess the conclusion I would draw from this is that your definition of the separation of powers in MVC and in how Cocoa does it is off. Cocoa is fairly rigid about adhering to the pattern, though there is an interesting contemporary movement within the Objective-C community towards MVVM.
You are correct the MVC practiced in most cocoa apps is not the MVC as it is defined in the text books. There are many variations of MVC employed by different frameworks. The MVC employed by tools with visual designers are heavily influenced by their visual designer implementation. With XCode you have story boards and nibs. The cocoa libraries and the way concerns are separated are influenced by this. If you want to take advantage of these tools, I would recommend understanding how concerns are separated by Xcode and work within this approach. Your code will coexist with it more smoothly. Apple documentation will help with this.
That being said, MVC is about separation of concerns. Separating concerns is hugely important in designing and maintaining software. Separating concerns properly can reduce dependency, reduce cyclomatic complexity, and make your code much more testable and maintainable. I think it is good that you are paying attention to this and whatever way you structure MVC should look to the reason why you are separating concerns as the guide to implementation.
Other than the “philosophical” aspects of it, is it a bad idea to have my controller also be my model?
It seems to save some programming time. I don’t have to create logic between the controller and the model, since it’s the same thing. And I can directly interact with the view.
What’s the point of separating the M and the C? Is modularity — that is, the ability to swap one model and controller set for another — the only reason to separate them? It seems to me that “swapping” modules out happens a lot less than (for example) having to update both the model and the controller because something in the model is changing.
It seems odd that a simple calculator, according to the MVC concept, should have both a controller and a view for its settings (like default settings, or something). I know this is a simple example, but it seems to apply to all cases (except maybe frameworks).
The primary reason is for reusability of code. If you’re only ever going to write one program in your professional life, then perhaps it doesn’t matter. If you plan to make a career of it, having reusable pieces is valuable. Well-designed model, controller and view classes are very easy to drop into other programs. I do this all the time.
Consider UITableViewController, which is a Controller. Now imagine if it were designed exclusively to handle music tracks (the Model), and you needed to create a completely different table-management class when you wanted to handle something else. Avoiding this nightmare is why MVC is heavily used in Cocoa.
There are other ways to split things up. Some languages subclass heavily rather than delegating. But in Cocoa, the primary means of splitting up programs is MVC, and it works very well.
EDIT: Just some more reasons from the world of developing commercial apps.
Memory handling is much easier in MVC. You can hold on to your model objects and throw away your view objects (and many of your controller objects) when they go offscreen.
It’s easier to serialize model objects that aren’t wrapped up with controllers and views, and it’s much easier to display the same data in multiple ways. Even in a “simple” text editor, you may want to be able to do split-screen, or have multiple windows showing the same document. In MVC that’s very easy.
If you need no flexibility now or in the future, you don’t need much architecture. But most real projects aren’t so simple. MVC grew out of Xerox’s experience with writing large programs and the difficulties encountered when everything was thrown together.
EDIT 2: I was looking at your earlier edit: “It seems odd that a simple calculator, according to the MVC concept, should have both a controller and a view for its settings (like default settings, or something).”
This is exactly the reason for MVC. It would seem crazy to have to re-code all of the things required for saving user settings specially for a Calculator app. You’d want a generic “please save these user settings” that was completely separate from the UI and that you could reuse. On OS X it’s called NSUserDefaults, and the Calculator app stores its configuration in exactly this way.
MVC is a standard pattern that is well understood in the development community, and for good reasons. The separation really makes things easy to read, easy to troubleshoot, easy to find, and easy to test, as individual components, each with its own area of responsibility.
Do you have to use it? of course not. But keeping the parts separate is generally considered a good idea.
The controller knows how to link a specific view to your model. The separation of model and controller, apart from improving documentation and maintainability, has the immediate benefit of allowing multiple views to display the same information from the model without adding any complexity to either.
That applies not just to multiple views in the same application, but also to the multiple variations in views you'll have across multiple versions of your application. Your model is insulated and logically clean.
Combining model and controller is a classic false economy in my opinion. It may feel like it saves a few minutes, but it costs significantly as an application develops and grows.
If it works for you then it works. Period. The reason for separation of Models, Views, and Controllers revolves around the idea that most development for enterprise applications is done by a team of developers.
Imagine 10 developers trying to work on your controller. But all they want to do is add something to the model. Now your Controller broke? What did they do?
The Models are usually separate components which can be re-used between Controllers. If you are absolutely certain you won't be re-using Models in multiple Controller, I don't really see a problem with blending these concerns.
I guess one could argue why even use MVC design if you are planning on deviating. Maybe there is a more suitable pattern to follow for your situation. Can you give us an example of something you've done where the Controller is the Model? It would help us understand what you are trying to do better.
MVC is all about management (separation of data, representation and business logic). So it's like this: if you run a small company, having a MS-sized management would be a real drag. But if you are a giant corporation, not having big middle management is impossible.
Honestly, in most of my college progamming assignments, I combined the models and controllers, because I didn't see the need for the separation. But working on big projects? The deficiency would be pretty obvious if you try to not separate. Just do what you feel right.
The model depends on neither the view nor the controller. This is one the key benefits of the separation. This separation allows the model to be built and tested independent of the visual presentation.
I just cannot seem to get my head around what exactly is the MODEL in MVP.
If I have a layered architecture PRESENTATION / APPLICATION / DOMAIN / INFRASTRUCTURE, what exactly is the MODEL?
DOMAIN objects accessed through
lower layers?
A separate object defined in the
PRESENTATION layer that maps to the
UI and uses data obtained from a
lower layer?
If someone could clear my understanding on what is the MODEL it would be greatly appreciated.
The Model is normally the group of classes/types/components that represent the core domain (business or otherwise) that your application operates within. These are the classes that perform the key logic required, often in the form of business rules, and also consume/manipulate data.
In your layered example, the Model would mostly be found in the Domain layer but could also be in the Application layer.
I think you're having difficulty understanding it because you are trying to combine two separate architectural patterns, or ways of looking at the application, being n-tier/n-layer versus MVP.
It's completely reasonable (and quite common) to use some sort of Model/View approach while at the same time applying layering in your application.
Maybe you should focus on them one at a time to start with and then overlay them when you are more familiar with both.
In any of the Model-View-* architectures, the Model is what describes the data in your application (and, if they fit the need, are passed in to the View for rendering).
If your application already has Domain objects, it very well may be the case that you could use them for your Model.
It doesn't matter what architectural guidelines you're following, M is always going to be the same thing. The Model is the piece that is specific to your domain. It's the part that really is what you're application is trying to do. The Model is supposed to represent your business domain. This goes for MVP, MVC, MVVM, etc.
If you were making a inventory system, then an Inventory class would most likely be in your Model, a Product would probably be there, an Order, you get the idea. These are the things that compose your domain logic.
The model is the data. This might just be data out of a database in DataSets, or it might be a complete domain model with objects representing your field of business.
The view is the UI, whether web pages or a Windows application or a mobile device application.
The presenter is the glue between the two and the brains of the whole outfit. Actions initiated by the view take place in the presenter. Generally in a WinForms application, for instance, a Button.Click event in my View simply calls a method on the Presenter, which then takes whatever action is necessary (and it may just be doing something back in the View).
The presenter holds a reference to the view (through an interface), and to the model. The view has a reference to the presenter (usually I strongly-type this, but it can be an interface as well). The model doesn't know about the presenter or the view.
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I found What are mvp and mvc and what is the difference but it didn't really answer this question.
I've recently started using MVC because it's part of the framework that myself and my work-partner are going to use. We chose it because it looked easy and separated process from display, are there advantages besides this that we don't know about and could be missing out on?
Pros
Display and Processing are seperated
Cons
None so far
MVC is the separation of model, view and controller — nothing more, nothing less. It's simply a paradigm; an ideal that you should have in the back of your mind when designing classes. Avoid mixing code from the three categories into one class.
For example, while a table grid view should obviously present data once shown, it should not have code on where to retrieve the data from, or what its native structure (the model) is like. Likewise, while it may have a function to sum up a column, the actual summing is supposed to happen in the controller.
A 'save file' dialog (view) ultimately passes the path, once picked by the user, on to the controller, which then asks the model for the data, and does the actual saving.
This separation of responsibilities allows flexibility down the road. For example, because the view doesn't care about the underlying model, supporting multiple file formats is easier: just add a model subclass for each.
Separation of concerns is the biggy.
Being able to tease these components apart makes the code easier to re-use and independently test. If you don't actually know what MVC is, be careful about trying to understand people's opinions as there is still some contention about what the "Model" is (whether it is the business objects/DataSets/DataTables or if it represents the underlying service layer).
I've seen all sorts of implementations that call themselves MVC but aren't exactly and as the comments in Jeff's article show MVC is a contentious point that I don't think developers will ever fully agree upon.
A good round up of all of the different MVC types is available here.
Jeff has a post about it, otherwise I found some useful documents on Apple's website, in Cocoa tutorials (this one for example).
I think another benefit of using the MVC pattern is that it opens up the doors to other approaches to the design, such as MVP/Presenter first and the many other MV* patterns.
Without this fundamental segregation of the design "components" the adoption of these techniques would be much more difficult.
I think it helps to make your code even more interface-based.. Not only within the individual project, but you can almost start to develop common "views" which mean you can template lot more of the "grunt" code used in your applications. For example, a very abstract "data view" which simply takes a bunch of data and throws it to a common grid layout.
Edit:
If I remember correctly, this is a pretty good podcast on MV* patterns (listened to it a while ago!)
MVC is just a general design pattern that, in the context of lean web app development, makes it easy for the developer to keep the HTML markup in an app’s presentation layer (the view) separate from the methods that receive and handle client requests (the controllers) and the data representations that are returned within the view (the models). It’s all about separation of concerns, that is, keeping code that serves one functional purpose (e.g. handling client requests) sequestered from code that serves an entirely different functional purpose (e.g. representing data).
It’s the same principle for why anybody who’s spent more than 5 min trying to build a website can appreciate the need to keep your HTML markup, JavaScript, and CSS in separate files: If you just dump all of your code into a single file, you end up with spaghetti that’s virtually un-editable later on.
Since you asked for possible "cons": I’m no authority on software architecture design, but based on my experience developing in MVC, I think it’s also important to point out that following a strict, no-frills MVC design pattern is most useful for 1) lightweight web apps, or 2) as the UI layer of a larger enterprise app. I’m surprised this specification isn’t talked about more, because MVC contains no explicit definitions for your business logic, domain models, or really anything in the data access layer of your app. When I started developing in ASP.NET MVC (i.e. before I knew other software architectures even existed), I would end up with very bloated controllers or even view models chock full of business logic that, had I been working on enterprise applications, would have made it difficult for other devs who were unfamiliar with my code to modify (i.e. more spaghetti).
One con I can think of is if you need really fast access to your data in your view (for example, game animation data like bone positions.) It is very inefficient to keep a layer of separation in this case.
Otherwise, for most other applications which are more data driven than graphics driven, it seems like a logical way to drive a UI.
If you follow the stackoverflow podcasts you can hear Jeff (and Geoff?) discuss its greatness. https://blog.stackoverflow.com/2008/08/podcast-17/. But remember that using these separate layers means things are easier in the future--and harder now. And layers can make things slower. And you may not need them. But don't let that stop you from learning what it is--when building big, robust, long-lived systems, it's invaluable.
It separates Model and View controlled by a Controller,
As far as Model is concerned, Your Models has to follow OO architecture, future enhancements and other maintenance of the code base should be very easy and the code base should be reusable.
Same model can have any no.of views e.g) same info can be shown in as different graphical views.
Same view can have different no.of models e.g) different detailed can be shown as a single graph say as a bar graph.
This is what is re-usability of both View and Model.
Enhancements in views and other support of new technologies for building the view can be implemented easily.
Guy who is working on view dose not need to know about the underlying Model code base and its architecture, vise versa for the model.
One of the major advantages of MVC which has not mentioned here is that MVC provides RESTful urls which enables SEO. When you name your Controllers and Actions wisely, it makes it easier for search engines to find your site if they only take a look at your site Urls. For example you have a car sale website and a page which displays available Lamborghini Veneno cars, instead of having www.MyCarSale.com/product/6548 referring to the page you can choose www.MyCarSale.com/SportCar/Lamborghini-Veneno url for SEO purpose.
Here is a good answer to MVC Advantages and here is an article How to create a SEO friendly Url.
Main advantage of MVC architecture is differentiating the layers of a project in Model,View and Controller for the Re-usability of code, easy to maintain code and maintenance. The best thing is the developer feels good to add some code in between the project maintenance.
Here you can see the some more points on Main Advantages of MVC Architecture.
![mvc architecture][1]
Model–view–controller (MVC) is a software architectural pattern for implementing user interfaces. It divides a given software application into three interconnected parts, so as to separate internal representations of information from the ways that information is presented to or accepted from the user.