I've read that best practice dictates fats models, skinny controllers.
Models should contain business logic such as getting a list of customers based on parameters sent from a controller.
Controllers should contain just enough logic to invoke methods within a model to return to a view.
However I see many examples and tutorials where there is logic within the controller such as a query that accesses a db to get a list of products. I was under the impression that the logic should live in a method inside a model. The controller can then invoke this method, rather than containing the actual logic to query the database.
So if I have a ProductController I might have a Index action which returns an Index View, and I would have a ProductModel which would house my logic to display certain products based on a query string(which the ProductController would pass to said model). Right?
So if I have a ProductController I might have a Index action which returns an Index View, and I would have a ProductModel which would house my logic to display certain products based on a query string(which the ProductController would pass to said model). Right?
That is correct. As per the Model-view-controller architecture:
The model manages the behavior and data of the application domain,
responds to requests for information about its state (usually from the
view), and responds to instructions to change state (usually from the
controller). In event-driven systems, the model notifies observers
(usually views) when the information changes so that they can react.
The view renders the model into a form suitable for interaction,
typically a user interface element. Multiple views can exist for a
single model for different purposes. A viewport typically has a one to
one correspondence with a display surface and knows how to render to
it.
The controller receives user input and initiates a response by making
calls on model objects. A controller accepts input from the user and
instructs the model and viewport to perform actions based on that
input.
Keep the data-related queries and operations in the model; stuff as much as you can in there in accordance with DRY (Don't Repeat Yourself). Make the functions reusable as much as possible so they can be ported into various controllers and used throughout the application as necessary.
The view should contain little - if any - logic outside of view-specific work.
Your controller functions should invoke the model functions required to retrieve and manipulate data, and should be as "thin" as possible (as you pointed out). The smaller and less involved the controller, the easier it will be to add asynchronous features that "don't reboot the application" on the front-end, making for a better user experience. (If you are concerned about this, anyway!)
The Add Controller dialog box in VS 2010 has the option of adding a scaffold with CRUD functions into the controller. This should tell you quite a bit above how the ASP.NET MVC dev. team views this debate.
Related
I'm trying to better understand the Rails workflow, specifically RCAV in relation to MVC. I know that MVC is the typical structure of a Rails app and that RCAV is the standard order of building various components of the app, however, I'm a little confused about the correlation between the two.
For example, I'm assuming the routes in RCAV are what link the models with views and controller in MVC. Is this correct?
I'm also guessing that the controller and view in RCAV are the same as the controller and view in MVC and simply represent the order in which you build them. Is this correct as well?
What I'm really stuck on is the Action part of RCAV - does this represent the Model component of MVC?
Sorry if my question doesn't make sense, just trying to get a better hang of the standard Rails workflow and the order in which various components of an app are typically built. I wish it were a little more distilled i.e. "first build Model, then Views, then Controller" but this whole separate RCAV thing is confusing me a little.
To your title question, no.
To elaborate, it's kind of confusing to map out RCAV (the sequence) against MVC (the framework), but I'll see if I can clarify. It's worth noting that the concepts themselves are not as complex as they seem, it's just confusing to explain.
RCAV
(Route-Controller-Action-View)
Routes are defined in config/routes.rb. You may think of them as the coupling between an HTTP Request and a Method (a specific type of method called an Action). On the one side it defines a path (ex. "/login") and one of the HTTP verbs (ex. "GET"), and says that whenever that type of request is made to that location, to perform the appropriate action. On the other side, an action is given in the form of the name of its controller (ex. "sessions"), and the name of the method itself (ex. "new").
Controllers receive the request according to the routes (so following the above example, if a user navigated to www.example.com/login, they would wind up in the sessions controller, which would be housed in app/controllers/sessions_controller.rb). The Controller may perform a number of functions prior to (and following) the action, in the form of callbacks. Callbacks are arguably a more advanced concept than what you need to understand right now, they are an important step (and the reason I explain RCAV as "Route >> Controller >> Action >> View", not as "Route >> Controller-Action >> View").
Actions are public methods in the Controller. Again, by our above example, you'll be hitting a method named "new" in the sessions_controller when a user navigates to www.example.com/login. Actions may perform any variety of functions, and there is often interaction with the model here (for instance, you may have a session model in app/models/sessions.rb with a method named "logout", and perhaps the first thing you do when you hit the login page is ensure the user is currently logged out by calling Session.logout. This is a poor design, but a decent example). Your action must "return" in one way or another. Assuming your action is meant to be consumed by a user directly through their browser (as opposed to as, say, a JSON or XML service), you will either render a view now, or redirect_to another action.
Views are, dare I say, the "end result" of the action. If nothing is specified, the above example will end by rendering "app/views/sessions/new.html.erb" for the user (Rails defaults to rendering the view whose path matches the controller and action, but as referenced above you could name something different). In this file you will also potentially make reference to the model associated with sessions (but this time inside of ERB tags, to be compiled into HTML).
MVC
(Model-View-Controller)
Models are classes tied, generally, to tables in a database. They contain validations for their fields, class methods, and instance methods. Say your database keeps track of sessions. Then you could potentially grab a list of sessions by calling Session.all anywhere in your application. You'd probably use an action in the Sessions controller to save this list to an instance variable (maybe #sessions), which could in turn be accessed in its appropriate view (<% #sessions.each do |s| %> ... <% end %>).
Views are essentially the web pages. They can bring along their own styles and scripts, and exist in the form of HTML files with embedded ruby. They are the end point of request made to your site (unless you're hitting a service which returns something like JSON or XML instead).
Controllers contain all the actions a user may access, often prepare variables via methods from the models, and generally drop the user into a view.
In Summation
A user accesses a route. The route drops them into a specific action within a controller. The controller (in the form of callbacks) and the action (on its own) prepare data from the model (via instance variables) to be consumed by the view. The view is then rendered into the users browser.
This is a simplification, but in the most standard cases, this is how the MVC framework (and rails, specifically) functions.
I've been working with the MVC pattern for a while now, but I honestly don't feel like I truly understand how to work with and apply the "Model" ... I mean, one could easily get away with using only the Controller and View and be just fine.
I understand the concept of the Model, but I just don't feel comfortable applying it within the pattern... I use the MVC pattern within .NET and also Wheels for ColdFusion.
"the Model represents the information (the data) of the application and the business rules used to manipulate the data" - yes, I get that... but I just don't really understand how to apply that. It's easier to route calls to the Controller and have the Controller call the database, organize the data and then make it available to the View. I hope someone understands where my confusion resides...
I appreciate your help in advance!
Look at it like this. When your client requests a page this is what happens (massively trimmed):
He ends up at your controller
The controller gets the necessary data from your model
The controller then passes the data to the view which will create your HTML
The controller sends the HTML back to the client
So client -> controller -> model -> controller -> view -> controller -> client
So what is the model? It is everything that is required to get the data required for you view!
It is services
It is data access
It is queries
It is object mapping
It is critical 'throw exception' style validation
Your controller should not be writing your queries if you are sticking to the pattern. Your controller should be getting the correct data required to render the correct view.
It is acceptable for your controller to do a few other things such as validating posted data or some if/else logic but not querying data - merely calling services (in your model area) to get the data required for your view.
I suppose it's just what you decide to call the different bits in your application. Whichever class you use to pass information from the Controller to the View can be seen as/called "The Model".
Typically we call Model our entity classes, and we call View Model the "helper" classes, for lack of a better word, we use when a "pure" entity (i.e., one that will be stored in the database) doesn't suffice to display all the information we need in a View, but it is all mostly a naming thing.
Your model classes shouldn't have any functions; ideally a model class will have only properties. You should see model classes as data containers, information transporters. Other than that they are (mainly) "dumb" objects:
// This would be a model class representing a User
public class User
{
public int ID { get; set; }
public string Name { get; set; }
public string Email { get; set; }
}
How do you actually pass information (whatever that might mean in your context) form your controller to your View and vice versa? Well then, that's your model. :)
Here is the way I have explained before:
Controller: determines what files get executed, included, etc and passes user input (if any exists) to those files.
View: anything that is used to display output to user.
Model: everything else.
Hope that helps.
Model is the code representation of your base Objects. While some less data-intensive systems may be light on the model end of MVC, I am sure you will always find an applicable use.
Let's take a contrived (but realistic) example to the usefulness of a model:
Say I am making a Blog. My Blog has Post objects. Now, Posts are used in and around the site, and are added by many users in the system. Our system was coded for people to enter HTML into their posts, but low and behold, people are starting to add pasted text. This text uses "\n" as the newline character.
With a model, this is a relatively simple fix. We simply make a getter that overrides postText:
public function get postText() {
return this.postText.replace("\n", "<br />");
}
Suddenly, we can affect behavior across the entire site with a few lines of simple code. Without the implementation of a model, we would need to find and add similar functionality where ever postText is used.
The Model in MVC is all about encapsulation and flexibility of a codebase as it evolves over time. The more you work with it and think about it in this manner, the more you will discover other cases that would have been a nightmare otherwise.
--EDIT (you have added to your question above):
Let us take this same example and use your Controller calling the database. We have 9 Controller classes for vaious pages/systems that use Post objects. It is decided that our Post table needs to now have a delete_fl. We no longer want to load posts with delete_fl = 1.
With our Post model properly implemented, we simply edit the loadPosts() method, instead of hunting down all the cases across the site.
An important realization is that in any major system, the Model is more of a collection of files than a single monolith. Typically you will have a Model file for each of your database tables. User, Post, etc.
model: word, sentence, paragraph
controller: for (word in sentence), blah blah... return paragraph
view: <div>paragraph.text</div>
The idea is to separate the concerns. Why not just have the controller logic in the view as well? The model represents the business objects, the controller manipulates those objects to perform some kind of task and the view presents the result. That way, you can swap an entire view for a different one and you don't have to rewrite the entire application. You can also have people work on different layers (model, controller, view) without affecting the other layers to a significant degree.
By combining the controller and the model, you are making your code less maintainable and extensible. You are basically not performing object-oriented programming as you are not representing the things in your database as objects, you are just taking the data out and sending it to the view.
The model contains business logic (i.e. significant algorithms) and persistence interaction - usually with a database. The controller is the MVC framework: Wheels, Struts, .NET's MVC approach. The view displays data that the controller retrieves from the model.
The big idea going on with MVC is that the view and model should be unaware of the controller - i.e. no coupling. In practice there's at least some coupling that goes on, but when well done should be minimal, such that it allows for changing the controller with low effort.
So what should be happening is a request hits the controller, typically a front controller, where there should be some glue code that you've written that either extends some controller object or follows some naming convention. This glue code has the responsibility for calling methods on the correct service layer object(s), packing that data inside of some sort of helper - typically an Event object - and sending that to the correct view. The view then unpacks data from the Event object and displays accordingly.
And when done well, this leads to a domain model (a.k.a. model) that is unit testable. The reason for this is that you've divorced the algorithms from any framework or view dependencies. Such that you can validate those independently.
We have a dashboard-style application with lots of individual bits of the screen that load asynchronously. Each of these bits really makes sense as its own action on the page's controller. However, the data will load more quickly if we reduce the number of http requests to 1. I'm considering creating an action that just returns a combination of results from several smaller actions, such that the web client can GET the actions separately or together. However, this seems like a hand-rolled solution to a common problem, so I'm wondering if there's built-in support for agglomerating actions in this way that I don't know about. Anybody?
In your core view, you can use the Html.RenderAction() method to render completely separate actions from another action.
Why don't you just use ViewModel containing all data needed for your dashboard and then create several partial views, feed them with data from ViewModel?
I have also an dashboard in my project, I did it this way and I am happy with the solution. I have DashboardController and its Index action just takes ViewModel (which aggregates all necesary data) and sends it to View. In that View, I have several partial views (each of them needs its own model) and I pass them data from my ViewModel. Inside that partial view are then references to specific actions (like CRUD for specific models).
When you do it this way, you can easily create partial views for specific models (Task, Project, User .. in my case). And then just use them as a pieces in your final layout. My ViewModel contains collections of Tasks, Projects and Users which I then simply pass to matching partial views.
I'm learning MVC and am having trouble deciding when I should create a new controller versus just adding an action and view associated with an existing controller. On the one hand, Single Responsibility would seem to say a controller should be limited to a few actions. When I try this, though, the number of classes grows exponentially (model, views and controller for each)- to the point I wonder if I'm going overboard.
For example, the default AccountController has Login, ChangePassword, and Register actions. I would tend to instead create a LoginController, PasswordController, and ProfileController, and related model classes. So where there was 1 class, there would be 3-6.
Is there any good rule of thumb on this?
You should dedicate a controller for each model type you're manipulating. The controller acts as a collection of actions that act upon those models. This is generally the rule of thumb, but sometimes a controller's scope transcends a single model.
The AccountController deals with all things authentication related. This is an example of going beyond a single model's scope to encompass authentication in general. What are the key parts of authentication? Retrieving users, changing passwords, etc.
I think you need to be pragmatic about it. I'm working on a project that consists of a StatsController. The number of actions is continuously growing (RandomStat, MostPopular, MostViewed, MostVoted, etc...) the list goes on and on. These actions are simple to satisfy since the StatsController's dependencies don't change. I'm using an IoC to satisfy what my Controllers need and when I start to see my Controllers needing references to new objects, this is a signal that they need to be broken apart.
If your LoginController, PasswordController, and ProfileController all rely on the same objects, why break them apart?
My current AccountController has 12 methods which to me is completely manageable.
I have another controller which currently has 34 methods but those are all tied to a single view and they each have around 8-10 lines of code max (check required parameters, update the model, and redirect as necessary).
They key is to encapsulate your business logic in an entirely separate module. That will allow your action handlers to remain extremely light weight and can make testing your business logic easier.
In Ruby on Rails Development (or MVC in general), what quick rule should I follow as to where to put logic.
Please answer in the affirmative - With Do put this here, rather than Don't put that there.
MVC
Controller: Put code here that has to do with working out what a user wants, and deciding what to give them, working out whether they are logged in, whether they should see certain data, etc. In the end, the controller looks at requests and works out what data (Models) to show and what Views to render. If you are in doubt about whether code should go in the controller, then it probably shouldn't. Keep your controllers skinny.
View: The view should only contain the minimum code to display your data (Model), it shouldn't do lots of processing or calculating, it should be displaying data calculated (or summarized) by the Model, or generated from the Controller. If your View really needs to do processing that can't be done by the Model or Controller, put the code in a Helper. Lots of Ruby code in a View makes the pages markup hard to read.
Model: Your model should be where all your code that relates to your data (the entities that make up your site e.g. Users, Post, Accounts, Friends etc.) lives. If code needs to save, update or summarise data related to your entities, put it here. It will be re-usable across your Views and Controllers.
To add to pauliephonic's answer:
Helper: functions to make creating the view easier. For example, if you're always iterating over a list of widgets to display their price, put it into a helper (along with a partial for the actual display). Or if you have a piece of RJS that you don't want cluttering up the view, put it into a helper.
The MVC pattern is really only concerned with UI and nothing else. You shouldn't put any complex business logic in the controller as it controls the view but not the logic. The Controller should concern itself with selecting the proper view and delegate more complex stuff to the domain model (Model) or the business layer.
Domain Driven Design has a concept of Services which is a place you stick logic which needs to orchestrate a number of various types of objects which generally means logic which doesn't naturally belong on a Model class.
I generally think of the Service layer as the API of my applications. My Services layers usually map pretty closely to the requirements of the application I'm creating thus the Service layer acts as a simplification of the more complex interactions found in the lower levels of my app, i.e. you could accomplish the same goal bypassing the Service layers but you'd have to pull a lot more levers to make it work.
Note that I'm not talking about Rails here I'm talking about a general architectural style which addresses your particular problem.
Perfect explanations here already, one very simple sentence as conclusion and easy to remember:
We need SMART Models, THIN Controllers, and DUMB Views.
http://c2.com/cgi/wiki?ModelViewController
The Rails way is to have skinny controllers and fat models.
Do put stuff related to authorization/access control in the controller.
Models are all about your data. Validation, Relationships, CRUD, Business Logic
Views are about showing your data. Display and getting input only.
Controllers are about controlling what data goes from your model to your view (and which view) and from your view to your model. Controllers can also exist without models.
I like to think of the controller as a security guard/receptionist who directs you the customer(request) to the appropriate counter where you ask a teller (view) a question. The teller (view) then goes and gets the answer from a manager (model), who you never see. You the request then go back to the security guard/receptionist (controller) and wait until you are directed to go another teller (view) who tells you the answer the manager (model) told them in response to the other teller's (view) question.
Likewise if you want to tell the teller (view) something then largely the same thing happens except the second teller will tell you whether the manager accepted your information. It is also possible that the security guard/receptionist (controller) may have told you to take a hike since you were not authorized to tell the manager that information.
So to extend the metaphor, in my stereotyped and unrealistic world, tellers (views) are pretty but empty-headed and often believe anything you tell them, security guard/receptionists are minimally polite but are not very knowledgeable but they know where people should and shouldn't go and managers are really ugly and mean but know everything and can tell what is true and what isn't.
One thing that helps separate properly is avoiding the "pass local variables from controller to view" anti-pattern. Instead of this:
# app/controllers/foos_controller.rb:
class FoosController < ApplicationController
def show
#foo = Foo.find(...)
end
end
#app/views/foos/show.html.erb:
...
<%= #foo.bar %>
...
Try moving it to a getter that is available as a helper method:
# app/controllers/foos_controller.rb:
class FoosController < ApplicationController
helper_method :foo
def show
end
protected
def foo
#foo ||= Foo.find(...)
end
end
#app/views/foos/show.html.erb:
...
<%= foo.bar %>
...
This makes it easier to modify what gets put in "#foo" and how it is used. It increases separation between controller and view without making them any more complicated.
Well, it sort of depends upon what the logic has to deal with...
Often, it makes sense to push more things into your models, leaving controllers small. This ensures that this logic can easily be used from anywhere you need to access the data that your model represents. Views should contain almost no logic. So really, in general, you should strive to make it so that you Don't Repeat Yourself.
Also, a quick bit of google reveals a few more concrete examples of what goes where.
Model: validation requirements, data relationships, create methods, update methods, destroy methods, find methods (note that you should have not only the generic versions of these methods, but if there is something you are doing a lot, like finding people with red hair by last name, then you should extract that logic so that all you have to do is call the find_redH_by_name("smith") or something like that)
View: This should be all about formatting of data, not the processing of data.
Controller: This is where data processing goes. From the internet: "The controller’s purpose is to respond to the action requested by the user, take any parameters the user has set, process the data, interact with the model, and then pass the requested data, in final form, off to the view."
Hope that helps.
In simple terms, generally,
Models will have all the codes related to table(s), their simple or complex relationships (think them as sql queries involving multiple tables), manipulation of the data/variables to arrive at a result using the business logic.
Controllers will have code/pointers towards the relevant models for the job requested.
Views will accept the user input/interaction and display the resultant response.
Any major deviation from these will put unwanted strain on that part and the overall application performance may get impacted.
Testing, Testing ...
Put as much logic as possible in the model and then you will be able to test it properly. Unit tests test the data and the way it is formed by testing the model, and functional tests test the way it is routed or controlled by testing the controllers, so it follows that you can't test the integrity of the data unless it is in the model.
j