This may sound like a stupid or unconstructive question but I'm a fan of not creating so many layers to reduce the amount of code that has to be written and maintained. In a classic scenario, the application logic would be in one class which calls the business layer. However, if the application logic is simple enough, would it be a crime if I were to put application logic in view models? In my case, this would entail calling the business layer in my view models.
yes, it would be a crime and completely destroy the mvc nature of... mvc.
if you have to, put application logic in your controller.
Surely it is not a crime. But it is good to understand why the Application Logic is "Normally" (what is normal) separated from the User Interface layer. The most important reason that is usually given for this separation is the ability to re-use the application logic when you application gets another User Interface implementation. This can be another technology, or another deployment model. Also for maintenance and readability this is often a best practice.
The fact that you are talking about a viewmodel probably means that you are creating a controller class that has no dependency on the view, according to MVC. This is already a separation in some sense from your user interface.
So my opinion: If you have the need / requirement / wish to modernize your user interface in the future or have multiple user interfaces target the same application logic, put some effort in a separate application logic component. Otherwise, you are not commiting a crime by implementing your application logic in your controller.
Related
I'm aware that in model-view-controller, the Model is the class part.
If I have a User class and instantiate an object, the object must refer to a single user from the database.
So I'll have the CRUD methods on the user, for that specific user.
But if I need a function to run a SELECT * FROM Users, should I create a function within the User class? Or a function in a helper file? Or in the controller? Where should it go, in order to respect the MVC pattern?
I mean, it makes no sense to instantiate a User object just to run a function to display the Users table.
I'm not sure if this will raise "primarily opinion based" flags. I just don't know where those functions should go. If you guys consider the question worth closing, it's ok. But tell me in the comments in which stack community I should ask this.
Back up a bit. Let's go foundational for a moment.
In the MVC pattern
The model is your state (in simple terms), meaning a representation of the data important to the business functionality you are working with
The view is a way of presenting the state to the user (NOTE user here could be another system, as you can use MVC patterns for service endpoints)
The controller ensures the model gets to the view and back out of the view
In a system designed with good separation of state, business functions are not present in the model, the view or the controller. You segregate business functionality into its own class library. Why? You never know when the application will require a mobile (native, not web) implementation or a desktop implementation or maybe even become part of a windows service.
As for getting at data, proper separation of concerns states the data access is separate not only from the model, view and controller, but also from the business functionality. This is why DALs are created.
Before going on, let's go to your questions.
should I create a function within the User class? This is an "active record" pattern, which is largely deprecated today, as it closely couples behavior and state. I am sure there are still some instances where it applies, but I would not use it.
Or a function in a helper file? Better option, as you can separate it out. But I am not fond of "everything in a single project" approach, personally.
Or in the controller? Never, despite Scott Gu's first MVC examples where he put LINQ to SQL (another groan?) in the controller.
Where should it go, in order to respect the MVC pattern?
Here is my suggestion:
Create a DAL project to access the data. One possible pattern that works nicely here is the repository pattern. If you utilize the same data type for your keys in all/most tables, you can create a generic repository and then derive individual versions for specific data. Okay, so this one is really old, but looking over it, it still has the high level concepts (https://gregorybeamer.wordpress.com/2010/08/10/generics-on-the-data-access-layer)
Create a core project for the business logic, if needed. I do this every time, as it allows me to test the ideas on the DAL through unit tests. Yes, I can test directly in the MVC project (and do), but I like a clean separation as you rarely find 0% business rules in a solution.
Have the core pull the data from the DAL project and the MVC project use the core project. Nice flow. Easy to unit test. etc.
If you want this in a single project, then separate out the bits into different folders so you can make individual projects, if needed, in the future.
For the love of all things good and holy, don't use the repository pattern. #GregoryABeamer has a great answer in all respects, except recommending you create repository instances to access your entities. Your ORM (most likely Entity Framework) covers this, and completely replaces the concepts of repositories and unit of work.
Simply, if you need something from your database, hit your ORM directly in your controller. If you prefer, you can still add a level of abstraction to hide the use of the ORM itself, such that you could more easily switch out the data access with another ORM, Web Api, etc. Just don't do a traditional unit of work with tens or hundreds of repository instances. If you're interested, you can read a series of posts I wrote about that on my blog. I use the term "repository" with my approach, but mostly just to contrast with the typical "generic" repository approach you find scattered all over the interwebs.
I'd use some kind of 'Repository' layer. Then, my controller calls the UserRepository GetAll method and sends the data to View layer.
I keep reading that the biggest layer in the MVC pattern should be the model. I've also heard that we should avoid putting logic on the controller layer. However, as my ASP.Net MVC 5 application is getting larger, I see that I'm getting heavy views, heavy controllers, and... extremely tiny models (they're not more than references to my SQL tables).
Yes, I admit, I could never manage to put any logic on my model.
I like the MVC pattern, and my website is working good, but I keep on thinking that I'm surely not doing things right...
Can you show me some useful links about how to write MVC code properly? Rick Anderson's (Microsoft) MVC 5 tutorial is fine, but once again, his models are indeed very tiny...
In my applications I put as much logic as possible in the domain models. On top of that there is an application layer which interacts with the database and domain models to perform application specific operations. The controller actions have as little code as possible and just call methods in the application layer.
In addition I usually have a view model for each view. Any logic that you have making your views "heavy" would go there.
One of the main reasons I try to put as much logic as possible in the domain models is to make unit testing easier. Logic in the application layer usually involves the database, which you will need to mock in order to test. Moving logic to the domain models makes testing easier and makes you code more reusable.
This is a pretty complex issue. I have an in depth blog post on the question if you're interested.
This answer is also pretty close to what I would suggest.
You're missing a service/business layer which should be injected in your controllers though "Dependency Injection". These services do all the heavy lifting.
Having Models without any methods or operations in them is a good thing. You're only storing this info anyway. They basically just get; set; data.
Use extra layer between models and controllers (for example repositories as data access layer).
I strongly recommend using ViewModels-they make code much more organized.
You should Create Some Classes that purely doing business logic and emit ViewModels for MVC view. Controller should respond to actions and the action method delegate the responsibility of getting the model to this business classes.
After some research on this issue, and taking into account some of these answers and comments, I realized that a medium sized MVC project can't rely exclusively on the 3 layered model. As the controller actions become bigger, the developer starts feeling the need of creating a 4th layer: the service layer. Like Gunnar Peipman correctly suggests in the following blog post, "Controller communicates with service layer and gets information about how access code claiming succeeded": http://weblogs.asp.net/gunnarpeipman/archive/2011/06/20/asp-net-mvc-moving-code-from-controller-action-to-service-layer.aspx
I have heard that the controller should be kept light and models heavy.
I am somewhat confused about the best practice on what should be kept in the controller and what should be kept in the model.
In our organization, we use Entity Framework where and put the tables there.
For the controller, we use LINQ and then send the info over to the view.
Kind of confused on what code should be in the Controller and in the Model.
DisclaimerThe whole topic is a giant mess. Especially when it comes to Web MVC. For all practical purposes it is impossible to use classical MVC pattern for web, because the view should be observing model. Theoretically you could implement something like that with WebSockets, but keeping a persistent model for each user is not a realistic solution.
Here is what you must know about MVC
The most important idea in both classical MVC and MVC-inspired patterns Separation of Concerns. It divides the application in two major layers:
Presentation layer
Governs the user interface. It deals with both creation of the interface and reacts to the user's manipulation of this interface. This interface might be GUI for a desktop application or HTML web page, but it also can be REST API or receiver-responder on a Mars rover. This is why a web application can implement MVC pattern in both frontend and backend.
The mandatory parts are views and controllers, but, in context of web, fully realized views usually also use multiple templates to create the interface.
Model layer
This is where all the business rules and logic lives. The M in MVC is not a single entity. Instead it is a layer, which contains different structures. Some of those structures are also responsible for interaction with storage.
What are the responsibilities of controllers ?
Controllers are part of presentation layer, which deals with user input. In context of web-based implementations, you will usually have 1:1 relationship between views and controllers, where controller receives the requests from browser and, based on the content of said requests, alters the state of model layer and view.
If you are using classical MVC or Model2 MVC, then that is the extent of controllers responsibilities.
In MVP and MVVM patterns, where you have a passive view, controller-like structures are responsible for acquiring information from model layer and passing it on to the current view instance. This post might provide some additional details on the MVC-inspired patterns.
But the controller is in no way responsible for any form of business logic. If it was, it would mean, that you have a leaking abstraction, because the structures of presentation layer would be doing work, which should be in the model layer.
Usually the controllers will the be simplest structures in you application.
What about the model ?
As mentioned before, model is a layer, which encompasses all of the domain business logic and related functionality. This layer , just like presentation layer, is made up from multiple groups of structures:
Domain Objects[1]
These structures are usually what people mean, when talking about "models". They are also known as model objects or business objects. This is where most of domain business logic ends up.
Data Storage Structures
This group would contain all of the classes, which abstract the interaction with storage (SQL databases, caching systems, noSQL, remote SOAP or REST APIs). They will usually implement some variation of data mapper or repository pattern , but you could be using some other solutions too, like unit of work. The implementation details are not so important. What is important is that they let you store data from and retrieve information into your domain objects.
Services
Or you could call the "components". There are high level abstractions in your model layer, which facilitate the interaction between domain objects and storage structures. The usually represent large chunks of model layer, like "recognition service", "mailers", "article management", and will provide the interface for presentation layer to interact with.
That's something of a religious debate.
Some like as little as possible code in their controller and other as little as possible in their model.
Do what feels natural to you in the project, but be consistent within it.
All else is dogma you can pick an example either way and make a case.
Model is the core of your application. It is best to think of models as of your business entities. Do you want to create a view of an invoice? Then Invoice be your model, it represents the underlying object.
Controller is just a way to handle requests from a client, retrieving the data from database (or updating them) and flushing out the responses.
Your thoughts about the application design should be model-centric, that's the important part.
In simple terms, Model represents the underlying data that your application will be using. It is to be designed in a way that it can be used across different applications.
For example, A model to represent News data can be used by console commands, Web service etc.
It is in model where you will have ur business logic defined, independent of the view.
Controller can be thought of as glue that binds Model and View together. They deal directly with client requests and accordingly interact with views and models.
In a well designed application, you data structure and business logic will be designed in a
Model, making it "heavy". While Controller will just interlink your model and view with the client requests, making it "light".
In the classic Model-View-Controller MVC pattern, your Model is essentially a "headless" application, with no UI and is completely UI-agnostics. It offers an API that is the functional core of the application.
The View is the user interface, however you choose to define it (web page? elevator control panel? something else?). A given application might have 1 view or it might have many views.
The Controller (or Controllers — like Views, you might have one to many Controllers for a given application) relays and transforms events, notifications and data between View and Model so as to preclude the Model from needing to know anything that is View-specific.
The idea is to isolate the core application (the Model) from the user interface (the View). From that some things follow:
The View is aware of and communicates with both Controller and Model (you're unlikely to try to wire up the View to another Model) and expected for the Controller to be aware of both View and Model.
The Controller is aware of and communicates with both View and Model.
The Model knows nothing of Controller or View.
Code that performs business logic should be in the Model, not in the Controller.
I'm no MVC expert, but try and concentrate on the fact that the controller should use the input from the user to direct them to the correct view.
I don't know if NerdDinner is an ideal example, but you can see Scott Hanselman et al does a little bit of data access from his EF context but pushes most of the other logic to service classes or helpers on the model.
I don't know if I agree with the 'models heavy' part, as I don't use the models as 'business objects'. If I really need a lot of 'business' logic, I will typically create that in a separate 'Domain' layer and may even have a separate Data Access layer on top of this. But for a lot of simple (see: non-enterprise) projects, this is overkill in my experience.
What are the responsibilities of one vs the other?
What kind of logic should go in one vs the other?
Which one hits services and databases?
How do I decide if my code should go in the viewmodel or the controller?
For the record, I am using ASP MVC, but since the question is architectural, I do not believe it matters what language or framework I am using. I'm inviting all MVC to respond
The ViewModel is a Pattern used to handle the presentation logic and state of the View and the controller is one of the fundamentals parts of any MVC framework, it responds to any http request and orchestrates all the subsequent actions until the http response.
The ViewModel Pattern: More info
In the ViewModel pattern, the UI and
any UI logic are encapsulated in a
View. The View observes a ViewModel
which encapsulates presentation logic
and state. The ViewModel in turn
interacts with the Model and acts as
an intermediary between it and the
View.
View <-> ViewModel <-> Model
The Controllers (Comes from the Front Controller Pattern): More Info
It "provides a centralized entry point
for handling requests."
HTTP Request -> Controller -> (Model,View)
--Plain Differences:--
While the ViewModel is an optional
pattern the Controller is a must, if
you are going the MVC way.
The ViewModel encapsulates
presentation logic and state, The
Controller orchestrates all the
Application Flow.
The ViewModel can be on the client side as well as server side.
Wherever it may be, the sole purpose of viewmodel is to play the
presentation data.
In MVC architecture Viewmodel is not mandatory but with out controller the request from the client cannot be processed.
Controller can be visualised as the main interface between client and server to get any response from the server. It processes the client request, fetches data from repository and then prepares the view data. Viewmodel can be visualised as view data processor/presenter thus an interface to manage the view more eloquently.
In the overall context of a web application we can say the controller is the application request handler whereas viewmodel is only the UI handler.
The Model-View-Controller (MVC) is an architectural design pattern which exists, primarily, to separate business logic from the presentation. Basically, you don't want your back-end touching your front. It typically looks like this:
The reasons for doing this is because, by separating the back-end and the front, you don't tie your user-interface directly to your data/work. This allows you to put new interfaces onto your business logic without affecting said logic. In addition, it also improves the ease of testing.
A simple example of where MVC comes in handy - let's say you have an application that manages your company's finances. Now, if you are correctly using MVC, you can have a front end that sits at some financier's desk and lets him handle transactions, manage the finances, etc. BUT, because the business logic is separate, you can also provide a front-end to your CEO's Blackberry that lets him see the current status of the business. Because the two front-ends are different, they can do different things while still providing (different types of) access to the data.
EDIT:
Since you updated your question a bit, I'll update my answer. There is no perfect science to the separation of MVC. There are some good rules of thumb, however. For example, if you are talking about GUI components, that is probably a view. (Are you talking about look and feel, usability, etc.) If you are talking about data and the "business" side of the house (databases, logic, etc), you are probably referring to a model. And, anything that controls the interaction between the two is most likely a controller.
In addition, it should be noted that, while Views and Models are typically "physically" separated, a controller can exist with a view when it makes sense.
You are correct when you say the framework (or even language) for MVC doesn't matter. The pattern itself is language agnostic and really describes a way to architect your system.
Hope that helps!
I think there's some value to learning received doctrine. But there is also value in understanding how the doctrine came to be the way it is.
Trygve Reenskaug is widely credited with inventing MVC. N. Alex Rupp's article Beyond MVC: A new look at the servelet architecture includes a History of MVC. In a section on Reenskaug's 1978 work at Xerox Palo Alto Research Center, there's a link to his paper Thing-Model-View-Editor: an Example from a planningsystem. There the pieces are described like this.
Thing
Something that is of interest to the user. It could be concrete, like a house or an integrated
circuit. It could be abstract, like a new idea or opinions about a paper. It could be a whole,
like a computer, or a part, like a circuit element.
Model
A Model is an active representation of an abstraction in the form of data in a computing
system
View
To any given Model there is attached one or more Views, each View being capable of
showing one or more pictorial representations of the Model on the screen and on hardcopy. A
View is also able to perform such operations upon the Model that is reasonabely associated
with that View.
Editor
An Editor is an interface between a user and one or more views. It provides the user with a suitable command system, for example in the form of menus that may change dynamically
according to the current context. It provides the Views with the necessary coordination and
command messages.
Rupp identifies Reenskaug's Editor as a Controller or Tool.
MVC Triads emerged in SmallTalk-80. The model was an abstraction of the real-world concept, the view was its visual representation, and the controller was the buttons and slider bars that allowed the user to interact with it (thereby "controlling" the view). All pieces in the triad were interconnected and could communicate with the other two pieces, so there was no layering or abstraction involved. Since then, Reenskaug has "preferred to use the term Tool rather then Controller." According to his notes, these are the terms he has used in later implementations
Some logic and model should be invoked to generate some data (structured or semi-structured). From this data the returned page/JSON/etc. is created, typically with only rudimentary outlining logic.
The first part (creating the data) is done by the controller (via the model usually). The second part - by the View. The ViewModel is the data structure being passed between controller and view, and usually contains only accessors.
Model represents your data and how it's manipulated. Thus, model touches the DB.
View is your UI.
Controler is the glue between them.
MVC stands for Model, View, Controller.
Model = Data (Database tables)
View = HTML, CSS, JavaScript, etc
Controller = Main logic, a contract between Model & View.
In simple and graspable terms,
MVC allows you to develop your applications in a way that your business data and presentation data are separated. With this, a developer and designer can work independently on a MVC app without their work clashing. MVC makes your app avail OOP too.
We have started using MVC framework and now we are bit confused where to write business-logic, in controllers or models?
For the project we are going to use WCF layer as DAL.
People have different views on Model & Controller, and think differently of writing business logic either in 'M' or 'C'.
What is the best practice?
I believe we will be accessing WCF (DAL) service in Model and applying all the business logic or filtering and then Controller accessing the data from Model.
These are my rules:
Controller
Mainly Pageflow . Determines what View is displayed next.
Has access to Services ( ie productService.GetProduct(Model.ProductID) )
Model
I have 2 of them.
POCO-Classes - used by all layers (BLL,DAL)
ViewModel - used by View and Controller for stronly typed views.
View
Hopefully mainly easy HTML
I try to have the layout in a way, that it is possible to have different kind of people work at the project: The frontend guy and the backend guy.
The backend guy will do the Service and Repository.
The Frontend guy will do Controller and Views. He also does ajax.
Try to keep -Business- logic and -Application flow- logic separate. Most people tend to mix those together as -business logic-
Most people keep their business logic in the model and this is considered best practice. Steve Sanderson who has written xVal endorses this method.
As I’ve discussed before, validation rules should go in your domain model, because the role of your model is to represent the workings of your business. It ensures that the rules will be enforced consistently, regardless of whether the UI coder remembers them or not.
Check out his post about xVal that talks about the problem you are discussing.
Do not think that model is supposed to be build from data access logic (wcf service in your case) only. I would recommend you to check out Domain Driven Design, it goes well with MVC. Controllers shouldn't contain any business logic. Controller action method should be ~20 or less lines. But that's just my opinion (made up from countless sources).