Given that I've got any number of controllers, how should they access the data saved in the model?
In a database driven application it's quite easy as all data can be fetched from one single object.
Should there be a namespace / singleton / global object which allows access to the data?
Should the model be passed to all controllers when they are created?
Some of the best practice being pass around is setting up a repository pattern like so within your model to abstract the data model form data mapping. I'd go into more detail but the first link gets you there.
Related
I am working on a custom Joomla MVC component.
My view has a form where the user enters an ID. I have retrieved the ID ($input_id) in the controller. Now I need to query the database to get the name WHERE ID = $input_id, then write the name to a different database table.
Can this all be done within the controller or do I have to pass my variables to the model somehow? Not sure of the correct way to achieve this within the MVC framework.
All data and data manipulation should be done in the model (e.g. model your data). The controller is there to determine the path of execution and which methods should be called (e.g. the manager aka controller determines what needs to be done).
Have a look at this tutorial which will help you understand MVC for Joomla better by taking you through the development of a simple component.
I’m having a philosophical problem with understanding how to use Models on MVC3.
I believe the problem lies from the fact that I come from WebForms :--)
Let's say I have 10 tables on my DB and as expected when I get them into my EF4, I get those Entity classes that represent the tables (and all their FK integer values).
When I want to display data on the View, I cannot display a select * from table because those FK integers means nothing to my users …and also because some data lies on related tables.
So my understanding is that I can create a Stored Proc, create a Complex Type that represent the actual data to display, coming from separate tables via different SQL joins.
QUESTION 1:
On the view, id MVC compliant to use as #model ..that Complex Type?
or shall I always use Models that are created on the Models folder? And if so, does that mean that I have to replicate the Complex Type on a new model inside the Models folder?
Question 2:
Is this the right way …to create specific SP to collect data that will be displayed or ..is it better to use linq and lambda to be applied to the EF4 Types that come from importing the DB into the EMDX designer.
Thoughts ??
FP
The correct way is to always define view models. View models are classes which are specifically tailored to the needs of a given view and would be defined in the MVC application tier. Those classes would contain only the properties that would be needed to be displayed by the view. Then you need to map between your domain models (EF autogenerated classes?) and the view models.
So a controller action would query a repository in order to fetch a domain model, map it to a view model and pass this view model to the view. Top facilitate this mapping you could use AutoMapper. A view shouldn't be tied to a domain model and always work with a view model. This works also the other way around: a controller action receives a view model from the view as action argument, maps it to a domain model and passes this domain model to the repository in order to perform some action with it (CRUD).
So a view model could be a class that is mapped from multiple domain models or multiple view models could be mapped to a single domain model. It all depends on how your domain looks like and how do you want to represent the information to the user.
As far as validation is concerned, I distinguish two types: UI validation and business validation. As an example of UI validation is: a field is required, or a field must be entered in a given format. A business validation is : the username is already taken or insufficient funds to perform wire transfer. UI validation should be done on the view models and business validation on the domain models.
I'm not sure why you need to use a stored proc, LINQ to Entities is able to generate complex types without needing to create stored procs (in most cases). You select subsets of data, just like you would with regular SQL.
As Darin says, the use of a View Model is appropriate for situations where you have a lot of complex data that isn't represented by a single entity. This View Model would contain multiple entities, or even multiple collections of entities. It all depends on how your data needs to be consumed.
I have a web application built on an MVC design.
I have a database which contains a large number of objects (forum threads) which I can't load into memory at once. I now want to display (part of) this collection with different filters in effect (kinda like what stackoverflow does with questions sorted by date, votes, tags etc).
Where do I implement the filtering logic? It seems to me that this must go into the model part of the application, as only models interact with the database (in my implementation). If I make the filtering a part of the view, then the view must access the database directly to get the list of filtered objects, right? I'd like to avoid this, because it exposes the database layout to the view. But at the same time, displaying different views of the same data should be implemented in the view part of the application, as they are just that -- different views of the same data.
So how do I resolve this? Do I create an additional model, say, FilteredThreadsList, and have it remember the filter to use, and then use a FilteredView to display the list of threads that FilteredThreadsList spits out?
Or do I have to build a ThreadQueryier that allows views to query the database for certain thread objects, so I can have the filtering logic in a view without exposing the database backend?
You should never query data from the view. I don't know what framework you are using in particular but as for Ruby on Rails (should be the same for other frameworks) we always pull the necessary data from the controller and store all that information into a variable. The variable will be accessed by the view which can help you avoid querying your database directly from the view.If the code to query the database gets too lengthy in the controller, insert that code into the model instead so it's more maintainable for your project in the future. Additionally, you can call this model method from multiple places in your application if needed. Good luck!
From an architectural point of view, the model should be having the code for filtering. This is so, because in many applications the code for filtering is not trivial and has a good amount of domain logic in it. (Think of filtering top gainers from a list of stocks). From your example as well, it looks the same since you might want to filter by vote or by date or by tags and then by answered or unanswered etc.
In some very simple applications that deal with search/list of entities and allows Create/Read/Update/Delete of an entity, the pagination, sorting and filtering logic is usually very generic and can be implemented in a controller base class that is inherited by all entity-specific controller classes.
The bottom line is this: if your filtering logic is generic put it in the controller else put it in the model.
Model, that's only bunch of entities.
View provides a visual representation of the data from model - use as much of views as you want. If your application is web based, you can fetch data into browser just once (AJAX) using and re-use them for different UI components rendered in the browser.
As for what entities and what view to use for their representation, I think it's work of Controller. If you need some support for it on "model layer", add it but avoid tight coupling.
I know it could be bad to use domain models as view models. If my domain model has a property named IsAdmin and I have a Create controller action to create users, someone could alter my form and get it to POST a IsAdmin=true form value, even if I did not expose such a text field in my view. If I'm using model binding then when I committed my domain model, that person would now be an admin. So the solution becomes exposing just the properties I need in the view model and using a tool like AutoMapper to map the property values of my returning view model object to that of my domain model object. But I read that the bind attribute on a class can be used to instruct the Model Binder which properties it should and shouldn't bind. So what really is the reason for making two separate classes (domain model and view model) that essential represent the same thing and then incure overhead in mapping them? Is it more a code organization issue and if so, how am I benefiting?
EDIT
One of the most important reasons I've come across for a View Model that's separate from the Domain Model is the need to implement the MVVM pattern (based on Martin Fowler's PM pattern) for managing complex UIs.
I have found that while my domain model gets me 85% of the way to having the fields I want, it has never covered 100% of the values I want on my view. Especially when it comes to permissions and whether or not a user should have access to certain portions of the view.
The design concept I attempt to follow is to have as little logic in my views as possible. This means I have fields in my view model like "CanViewThisField" or "CanEditThisField." When I first started with MVC I would have my domain model be my view model and I was always running into the scenario where I needed just one or two more fields to make my view less cluttered. I've since gone the View Model/Model Builder route and it has worked wonderfully for me. I don't battle my code any longer but am able to enhance my view model as I need to without affecting the domain model.
Another good reason to have a ViewModel is paging large sets of data. You could pass the view an array of Person ( Person[] ) but metadata such as the number of pages, the number of the current page, the size of the page would not belong on the Person class.
Therefore a PersonListViewModel would solve this issue.
A ViewModel holds only those members which are required by the View. They can usually be thought of as a simplification or a "flattening" of the underlying domain model.
Think of them like this:
ViewModel: this is the data that is appropriate to render on this
view
Domain model: this is all the information my application needs
about this entity in order to perform all it's functionality
For example, my Order class has a member called Customer which is a composition association, that is, my Order has a Customer. This Customer object has members such as Firstname, Lastname, etc... But how would I show this on a "details" view of the order or a list of Orders and the Customers who placed them?
Well, using a ViewModel I can have an OrderListItemViewModel which has a CustomerName member and I can map the combination of Firstname and Lastname from the Customer object to this. This can be done manually, or much preferably using Automapper or similar.
Using this approach, you can have multiple Order ViewModels that are specific to different views, e.g. the Order list view might render the customer name in a different way to the Order details view.
Another advantage of ViewModels is that you can cut down on extraneous data not required of the underlying domain object on a view, e.g. if I'm viewing a list of orders, do I really want to see all the customer's contact information, billing details, etc...? I guess that depends on the purpose of the list but, probably not.
Sometimes you need to display the data in a specific manner (ie, displaying a date in the format mm/dd/yyyy vs. yyyy/mm/dd) and often it is easier to make this property in the view and not in the domain model, where you would (or should) have a mapping to a column in your db.
you need to remember
that your domain model classes are only used internally; that is, they are never sent to the
client. That’s what your service model types (View Model types) are used for—they represent the data that will be going back and forth between the client and your service.
So I have read some of the similar asked questions, but I don't know if the right questions were asked. It appears there are different ways to get data from multiple entities passed into your View Model, but I want to go about it the correct way.
I basically have 2 entities available in my controller, and I need to pass different information from both entities to my view. I have read about creating a SomeNameViewModel class that would be instantiated in my controller ViewResult method. With the SomeNameViewModel object assigning the data into a single object to pass to the View Model
Example:
public ViewResult List()
{
var vm = new SomeNameViewModel {
products = _prodRepo.All();
catName = <Some Expression>;
return View(vm);
}
But is this the best practice way to go about this?
I am using Nhibernate: So would this be better handled in my Fluent Mapping so that I have access to the other entity through the one-to-one mapping?
Using a model per view is a common (and good) way to go about providing data to your views. View models can encompass values from more than one entity type and may contain ancillary data as well. You might want to also consider using view-specific models for any entities contained in your view model to further isolate your view from your domain objects. This way you can provide to your view exactly the data they need and no more and, if your domain model changes, you may be able to only modify how the view-specific model gets updated from the domain model rather than propagating the change throughout your views.