Coming from a Silverlight background, MVVM is solidly planted in my mind. Moving to MVC, although rewarding, has been something of a paradigm shift for me.
One of the questions I have is about using EditorForModel when the strongly typed view has been passed a ViewModel with the object to be editted as a property, rather than the POCO being directly passed in as the model, with no viewmodel encapsulated around it.
How can I use EditorForModel on a property of the model, rather than the whole model itself? I went looking for something akin to #HtmlHelper.EditorForModel(model.Customer), but coulndt find an overload. It seems you can only generate an editor for the whole model...
(where customer is a good 'ol poco)
You could try -
#Html.EditorFor(m => m.Name)
Related
NO this is not a duplicate!
In MVVM viewModel a PersonViewModel wraps a Person model.
In MVC viewModel a PersonViewModel does/should not wrap a Person.
Instead Automapper is used else it would be a hybrid PersonViewModel.
So the mvc alpha geeks on SO say
What is the reason that it is not allowed/wanted for mvc that a viewmodel wraps a model?
The context of my question is this:
When I dont wrap my models inside the viewmodel then I have to assign all model properties to the viewmodel properties in the controller. Thats a mess. Then people tell to use AutoMapper which is partly fine and partly terrible because now I have viewModel logic in the AutoMapper profile classes and I have viewModel logic in the viewmodels which belong there.
Now I have to test automapper AND viewModels. I would like to have a consistent architecture where I test only viewModels but then I have to wrap my models.
Thats the origion of my question.
It's perfectly allowed, but it's not part of the structure of MVC. If you start wrapping data models with view models, then you're beginning to adhere to MVVM.
Which pattern you use depends on many factors, and is often largely down to your personal preference. Hence, there's nothing inherently wrong in using one pattern over another, but the point of doing so is to adhere to that certain set of principles to achieve a consistent architecture.
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For the ViewBag, I heard it was a no-no to use.
I would assume have the content from the ViewBag should be incorporated into a view model?
Question:
Is my assumption above the best practice. (Not to use a ViewBag and second to have it in the view model)
Are there situations where a ViewBag is absolutely necessary?
ViewBag is a dynamic dictionary. So when using ViewBag to transfer data between action methods and views, your compiler won't be able to catch if you make a typo in your code when trying to access the ViewBag item in your view. Your view will crash at run time :(
Generally it is a good idea to use a view model to transfer data between your action methods and views. view model is a simple POCO class which has properties specific to the view. So if you want to pass some additional data to view, Add a new property to your view model and use that.Strongly typed Views make the code cleaner and more easy to maintain. With this approach, you don't need to do explicit casting of your viewbag dictionary item to some types back and forth which you have to do with view bag.
public class ProductsForCategoryVm
{
public string CategoryName { set;get; }
public List<ProductVm> Products { set;get;}
}
public class ProductVm
{
public int Id {set;get;}
public string Name { set;get;}
}
And in your action method, create an object of this view model, load the properties and send that to the view.
public ActionResult Category(int id)
{
var vm= new ProductsForCategoryVm();
vm.CategoryName = "Books";
vm.Products= new List<ProductVm> {
new ProductVm { Id=1, Name="The Pragmatic Programmer" },
new ProductVm { Id=2, Name="Clean Code" }
}
return View(vm);
}
And your view, which is strongly typed to the view model,
#model ProductsForCategoryVm
<h2>#Model.CategoryName</h2>
#foreach(var item in Model.Products)
{
<p>#item.Name</p>
}
Dropdown data ?
A lot of tutorials/books has code samples which uses ViewBag for dropdown data. I personally still feel that ViewBag's should not be used for this. It should be a property of type List<SelectListItem> in your view model to pass the dropdown data. Here is a post with example code on how to do that.
Are there situations where a ViewBag is absolutely necessary?
There are some valid use cases where you can(not necessary) use ViewBag to send data. For example, you want to display something on your Layout page, you can use ViewBag for that. Another example is ViewBag.Title (for the page title) present in the default MVC template.
public ActionResult Create()
{
ViewBag.AnnouncementForEditors="Be careful";
return View();
}
And in the layout, you can read the ViewBag.AnnouncementForEditors
<body>
<h1>#ViewBag.AnnouncementForEditors</h1>
<div class="container body-content">
#RenderBody()
</div>
</body>
1) Is my assumption above the best practice. (Not to use a ViewBag and
second to have it in the view model)
You should use viewmodels instead of passing data via ViewBag as much as possible.
2) Are there situations where a ViewBag is absolutely necessary?
There is no situation where a ViewBag is absolutely necessary. However, there are some data I personally prefer using ViewBag instead of View Model. For example, when I need to populate a dropdown box for predefined values (i.e Cities), I use ViewBag for carrying SelectListItem array to view. I prefer not to pollute my ViewModels with this data.
1) Is my assumption above the best practice. (Not to use a ViewBag and
second to have it in the view model)
Yes.
2) Are there situations where a ViewBag is absolutely necessary?
No. Everything that you have stored in a ViewBag could go into the view model passed to the view.
The issue with ViewBags and the recommended best practice boils down to compile time checking. ViewBags are just dictionaries and with that you get 'magic' strings, so if you end up changing the object type of one of the viewbag items or the key name you won't know until runtime, even if you precompile the views using <MvcBuildViews>true</MvcBuildViews>.
Sticking to view models is best, even if you have to alter them to fit a specific view now and again.
I have found some use for ViewBag where there is common functionality across all pages, and the functionality does not depend on the page being shown. For example, say you are building StackOverflow. The job board appears on each page, but the jobs shown have nothing to do with the page (my usage was similar in concept). Adding a property to each ViewModel would be difficult and time consuming, and a lot of fluff to your tests. I don't think it is worth it in this situation.
I have used a base ViewModel class with the cross cutting data, but if you more than one (e.g., jobs & list of stack exchange sites), you either have to start stuffing extra data in, or some other abuse of a ViewModel, plus you need a ViewModel builder to populate the base data.
As for the magic strings problem, there are a lot of solutions. Constants, extension methods, etc.
With all that said, if you have something that is displayed on your page that depends on the context of the page, a ViewModel is your friend.
Erick
No. Use ViewModels.
No. If you design a perfect ViewModel, you never need a ViewBag.
If you cannot re-design EXISTING ViewModel use ViewBag.
If there were no use cases for it, it wouldn't be implemented in the first place. Yes you can do everything with ViewModels, but what if you don't really need one? One such scenario is editing entities. You can pass DTO directly as a model.
#model CategoryDto
<div class="md-form form-sm">
<input asp-for="Name" class="form-control">
<label asp-for="Name">("Category Name")</label>
</div>
But what if you want to select Category parent? Entity DTO ideally holds only it's own values, so to populate select list you use ViewBag
<select asp-for="ParentId" asp-items="ViewBag.ParentList">
<option value="">None</option>
</select>
Why do this? Well if you have 50 types of entities each with some sort of select from different values, you just avoided creating 50 extra ViewModels.
I thought I'd give my opinion on this, as I've used the ViewBag extensively.
The only real benefits you'll get from using it are for a small project, or in cases where you have a new project and just want to get the ball rolling and not have to worry about creating loads of model classes.
When your project is more mature, you may find issues with unexpected behaviour caused by using weak typing all over your application. The logic can be confusing, difficult to test and difficult to troubleshoot when things go wrong.
I actually went down the route of completely removing the ViewBag from my applications, and preventing other developers from using it within the same codebase by throwing compilation errors when they try to, even within Razor views.
Here's a sample ASP.NET 5 project on GitHub where I've removed it: https://github.com/davidomid/Mvc5NoViewBag
And here's a blog post where I explain the motivations for removing it and an explanation on how the solution works:
https://www.davidomid.com/hate-the-aspnet-mvc-viewbag-as-much-as-i-do-heres-how-to-remove-it
2.Are there situations where a ViewBag is absolutely necessary?
In some case you'll need to share your data from the Controller across the layouts, views and partial views. In this case, ViewBag is very helpful and I doubt there's any better way.
At the risk of opening up an old can of worms here, let me offer a tiny bit of insight. Regardless of what might be the "best practice," let me offer the real-world experience that the extensive use of ViewBag can be a nightmare source of niggling, hard to find bugs and issues that are an utter nuisance to track down and resolve. Even if an agreeable notion or rule for the use of ViewBag can be established, they too easily become a crutch for junior developers to rely on to distraction AND discourage the development of proper, strongly typed ViewModels.
Unfortunately, too many "tutorial" YouTube videos show the use of ViewBags for a demonstration purposes and offer little to no insight on when such a practice isn't appropriate for production code. Yes, there may be times when use of the ViewBag may be a suitable solution to a given problem, but can lead to a long and winding road of frustration and poor maintainability. At the risk of overcorrecting in the cautious direction, I would encourage younger developers not to rely on the ViewBag until they get more experience with MVC, develop a natural sense of when and how ViewModels are useful, and then after that time develop a more seasoned sense of when the use of the ViewBag is appropriate.
Looking through the project we are working on (ASP MVC 3.0), I have seen this part of code in one of my ASPX views:
var groups = Model.GroupBy(t => new { t.OrganizationUnitName, t.OrganizationUnitId, t.ServiceTermDate }).OrderBy(m =>m.Key.ServiceTermDate).ThenBy(m => m.Key. OrganizationUnitId);
foreach (var group in groups){
var data = group.Select(t => new
{
t.PersonFullName,
t.ServiceTermStatusName,
t.VisitTypeName,
SubType = ControllerHelper.LocalizedPersonSubType(t.PersonSubTypeName),
t.MedicalServiceName,
t.PersonId,
t.ServiceTermId,
t.Phone,
CountryName = t.Name,
PersonUniqueNumber = t.GetUniqueIdentifyingNumber(),
}).OrderBy(m => m.HoursFromMinutesFrom);
foreach(var item in data){%>
...............
//render table and table rows, for sample
<tr>
<td><%= item.PersonFullName%></td>
</tr>
..............
<%}%>
<%}%>
<%}%>
I am not sure this is best coding practice, shouldn't LINQ statement be placed in controller helper (or somewhere else) instead in view directly? And if I'm right, how that could be done utilizing best coding practices?
Thank you in advance
It seems that LINQ which is performed directly in the view is not only at the wrong place but also it raise another interesting question: if we place it into service layer or controller or controller helper, then how it would be passed in this case - anonymous type IGrouping to strongly typed view?
Personally, I wouldn't use LINQ in the view. Do this in the controller for unit testing purposes.
If there is logic being performed, in a larger application I'd even move it out to a services assembly which would contain all of your LINQ queries.
Your view should be as basic as possible. Any ordering, grouping or sorting should be done in your controller (preferably with the help of a helper method which is re-usable for different actions across the application).
The philosophy of ASP.NET MVC (and I'd say of the MVC paradigm in general) is:
Put as little code as possible in the view. Ideally, you should just
reference data in the model class, perhaps with some loops or
conditional statements.
Do not put complex application logic in the controller methods.
Ideally, these methods should just collect the input data from the user
(if any), perform all the appropriate security and data validations, then pass the data to an application logic (or business logic)
class, then redirect to the appropriate view with the new model data
obtained from the logic class. (I once read that a controller method should have no more than 10 lines of code; maybe this is a bit exagerated but you get the point)
So I would say: not only the view should be LINQ free; the controller should be like this too.
Yes you can do it on View but i prefer to use Business logic work done through
controller rather than on View.
View is just used to display the GUI that must be as basic and simple to reduce the complexity of the GUI.
To make application code consistent, maintainable and reusable put these type of logic on Business Logic Classes except writing on Controller or view.
MVC is about abstraction of concerns.
The code you have posted above is breaking the most important rule of MVC. The view is the view, it has no business logic or data access code. It simply displays data that it is given to it in a nice way that can allow for presentation and user interaction. Think of the view as something you could give to a designer who knows nothing of asp.net.
The problem you have above is a perfect candidate for a ViewModel. The "Model" variable that is being used here is wrong, since you are taking it and then changing it to display something different. If the domain model doesn't fit then the controller should create a ViewModel that looks exactly as the view expects. There are a few ways of doing this. But one way is for example:
public ActionResult DoSomething()
{
List<DomainModel> modelCollection = getListOfDomainModels();
// Perform ViewModel projection
var viewModelList = modelCollection
.GroupBy(t => new { t.OrganizationUnitName, t.OrganizationUnitId, t.ServiceTermDate })
.OrderBy(m =>m.Key.ServiceTermDate)
.ThenBy(m => m.Key. OrganizationUnitId)
.Select(p => new MyViewModel()
{
FullName = t.PersonFullName,
StatusName = t.ServiceTermStatusName,
// etc ...
});
return View("DoSomethingView", viewModelList);
}
Now your Model variable will contain the correct model for the view.
Depending on your project's size and requirements you can make this alot better by performing the whole query in another layer outside of the controller and then projecting to a ViewModel inside your controller.
You should not be doing it in either the View or the Controller. Thus without giving you to much to chew at a a time you will want to have Separation of concerns (SOC) and keep it DRY (Don't repeat yourself) otherwise it becomes a maintenance nightmare.
If you put that code in the view (which is the worst place for it). 1. What happens if you want to use same or similar code elsewhere? 2. How will you step through debugging your code in this manner?
This is the equivalent of placing sql queries in a ASP.NET webforms .aspx file, not even in the code behind .aspx.cs file. Not using your model or a repository pattern and putting the code in the controller is another bad idea as a controller ActionResult has a Single Responsibility (SRP) of handling request, by smothering it with this code you have introduced an anti-pattern. Keep the code clean in organized areas. Don't be afraid to add class library projects. Look up the Repository pattern and eventually get to the point of doing unit testing and using DI (Dependency Injection) not just for unit test, but for a loosely coupled / highly cohesive application.
I like the way model binding in django works: you send stuff that you need in a Json-like way:
'param1': val,
'param2': val
In ASP.NET MVC you can't do it primarily because C# is a static language. You can use ViewData but it's ugly and not recommended.
So I had to create dozens of ViewModels for every view: IndexViewModel, AboutViewModel, etc. And today I got an idea: why not just create one Model class and have Visual Studio generate all necessary fields? It's almost like in django.
return View(new Model
{
Param1 = "asd",
Param2 = "sdf"
});
Param1 & Param2 are not members of the Model class, but Visual Studio will automatically generate them.
Now my question is, is it gonna work? The thing is that there will be a lot of fields in this Model class. And when we pass it to a view, only a small percentage of fields made for that view in particular will be used. Is it gonna be bad performance wise?
Thanks
If you have all these properties on your ViewModel which aren't used (i.e null or whatever) it isn't really going to impact performance. What it will impact however, is your design.
Generally speaking, one model to rule them all as you are proposing is a bit evil and goes against separation of concerns. ViewModel's should be very simple and should be tailored to the view. ViewModel's shouldn't really provide the view with more or less data than what the view needs in order to render.
Consider this....
You have a generic model with 15 properties on it and you only set a handful of them. Somebody else designs a new view and looks at the model, they may not know which of those properties are sent and under what conditions they are set. Consequently they may be attempting to display data that does not exist. This isn't a very clean approach.
I would stick to individual view models and where there is common functionality between views, create an abstraction or base ViewModel from which other view models can extend.
Edit: One other thing you could do is use the new MVC 3 (still in preview) syntax (dynamic) for setting ViewData properties directly as if they were properties.
So rather than doing
ViewData["FirstName"] = "Bob";
You can do
ViewModel.FirstName = "Bob";
This gives you dynamic variables automatically in MVC 3.
Have a look a Clay the 'malleable' object model being used by the Orchard Project.
http://weblogs.asp.net/bleroy/archive/2010/08/16/clay-malleable-c-dynamic-objects-part-1-why-we-need-it.aspx
http://weblogs.asp.net/bleroy/archive/2010/08/18/clay-malleable-c-dynamic-objects-part-2.aspx
There's no reason it shouldn't work.
You can even skip the Model class and create an anonymous type with just the members you need.
return View(new { Amount = 108, Message = "Hello" });
The problem using anonymous types is that you're giving up on auto-completion in the view since you won't be able to type the view according to the model.
Just use dynamic
The 'RenderPartial()' method in ASP.NET MVC offeres a very low level of functionality. It does not provide, nor attempt to provide a true 'sub-controller' model *.
I have an increasing number of controls being rendered via 'RenderPartial()'. They fall into 3 main categories :
1) Controls that are direct
descendants of a specific page that
use that page's model
2) Controls that are direct
descendants of a specific page that
use that page's model with an
additional key of some type.
Think implementation of
'DataRepeater'.
3) Controls that represent unrelated
functionality to the page they appear
on. This could be anything from a
banner rotator, to a feedback form,
store locator, mailing list signup.
The key point being it doesn't care
what page it is put on.
Because of the way the ViewData model works there only exists one model object per request - thats to say anything the subcontrols need must be present in the page model.
Ultimately the MVC team will hopefully come out with a true 'subcontroller' model, but until then I'm just adding anything to the main page model that the child controls also need.
In the case of (3) above this means my model for 'ProductModel' may have to contain a field for 'MailingListSignup' model. Obviously that is not ideal, but i've accepted this at the best compromise with the current framework - and least likely to 'close any doors' to a future subcontroller model.
The controller should be responsible for getting the data for a model because the model should really just be a dumb data structure that doesn't know where it gets its data from. But I don't want the controller to have to create the model in several different places.
What I have begun doing is creating a factory to create me the model. This factory is called by the controller (the model doesn't know about the factory).
public static class JoinMailingListModelFactory {
public static JoinMailingListModel CreateJoinMailingListModel() {
return new JoinMailingListModel()
{
MailingLists = MailingListCache.GetPartnerMailingLists();
};
}
}
So my actual question is how are other people with this same issue actually creating the models. What is going to be the best approach for future compatibility with new MVC features?
NB: There are issues with RenderAction() that I won't go into here - not least that its only in MVCContrib and not going to be in the RTM version of ASP.NET-MVC. Other issues caused sufficent problems that I elected not to use it. So lets pretend for now that only RenderPartial() exists - or at least that thats what I've decided to use.
Instead of adding things like MailingListSignup as a property of your ProductModel, encapsulate both at the same level in a class like ProductViewModel that looks like:
public class ProductViewModel() {
public ProductModel productModel;
public MailingListSignup signup;
}
Then get your View to be strongly-typed to the ProductViewModel class. You can access the ProductModel by calling Model.productModel, and you can access the signup class using Model.signup.
This is a loose interpretation of Fowler's 'Presentation Model' (http://martinfowler.com/eaaDev/PresentationModel.html), but I've seen it used by some Microsoft devs, such as Rob Conery and Stephen Walther.
One approach I've seen for this scenario is to use an action-filter to populate the data for the partial view - i.e. subclass ActionFilterAttribute. In the OnActionExecuting, add the data into the ViewData. Then you just have to decorate the different actions that use that partial view with the filter.
There's a RenderPartial overload I use that let's you specify a new ViewData and Model:
RenderPartial code
If you look at the previous link of the MVC source code, as well as the following (look for RenderPartialInternal method):
RenderPartialInternal code
you can see that if basically copies the viewdata you pass creating a new Dictionary and sets the Model to be used in the control. So the page can have a Model, but then pass a different Model to the sub-control.
If the sub-controls aren't referred directly from the main View Model, you could do the trick Marc Gravell mentions to add your custom logic.
One method I tried was to use a strongly typed partial view with an interface. In most situations an agregated ViewModel is the better way, but I still want to share this.
<%# Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<IMailingListSignup>" %>
The Viewmodel implements the interface
public class ProductViewModel:IMailingListSignup
Thats not perfect at all but solves some issues: You can still easily map properties from your route to the model. I am not shure if you can have a route parameter map to the properties of MailingListSignup otherwise.
You still have the problem of filling the Model. If its not to late I prefer to do it in OnActionExecuted. I dont see how you can fill a Model in OnActionExecuting.