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ASP.NET MVC - Best practices when passing dependencies

I have a question, that I tried to Google but honestly, I don't really know how to search or even ask this particular question.
Let's imagine I have the following:
Controller
[HttpGet]
public virtual ActionResult Summary()
{
var summaryViewModel = new CheckoutSummaryViewModel()
{
Products = ProductViewModel.BuildListFromShoppingCart(GetShoppingCart())
};
return View("_Summary", summaryViewModel);
}
ProductViewModel
public class ProductViewModel
{
public string Name
{
get; set;
}
public static List<ProdutoCheckoutViewModel> BuildListFromShoppingCart(ShoppingCart shoppingCart, IMappingService mappingService)
{
var itemsInCart = new List<ProductViewModel>();
foreach (var item in shoppingCart.ItemsInCart)
{
var itemViewModel = mappingService.Map<Product, ProductViewModel>(item.Product);
itemViewModel.Quantidade = item.Quantity;
itemsInCart.Add(itemViewModel);
}
return itemsInCart;
}
}
This is not production code. Is just so I can explain what I mean.
Is this the correct way of doing this?
Is there a better way than using static for building the list? I really don't want to do it inside the controller.
Passing IMappingService to the method does not look right. But maybe I'm just being picky. Is it the best way?
Another case, where I need to pass Session State to a static helper class.
public static Guid GetCheckoutId(HttpSessionStateBase session)
{
return (Guid)session["checkoutId"];
}
Or, also, sometimes I need to pass as parameter, to helper methods, my "unifOfWork", since I use the repository pattern.
I've come accross this "problem" a lot and I did not find the best way, yet, to do it.
PS: If any of you has a better title for this question, please tell me so I can update it.

Controller
If you use DI, it would look something like this:
public class CheckoutController
{
private readonly ICheckoutService _checkoutService;
public CheckoutController(ICheckoutService checkoutService) =>
_checkoutService = checkoutService;
[HttpGet]
public virtual ActionResult Summary()
{
var shoppingCartData = _checkoutService.GetShoppingCart(Session["..."]);
// The viewmodel here could be returned by your service or the service
// would return all required data and the viewmodel simply transforms that Dto into what is needed by the UI
var summaryViewModel = new CheckoutSummaryViewModel()
{
Products = shoppingCartData
};
return View("_Summary", summaryViewModel);
}
}

.NET MVC Null Object which initialized in constructor of ViewModel using RedirectToAction

I have two controllers(controllerA.actionA & controllerB.actionB) which share the same view & ViewModel(ViewModel_Shared).
So, in both Controller, I use RedirectToAction to redirect to a third controller(controllerC.actionC) which points to the shared view.
All three Actions are in different Controller.
When ActionA or ActionB was invoked All the parameters that post from view was sent to the modelC in actionC successfully.
However, when I try to feed data into the object(Item), NullReference exception was thrown. the object(Item) was NULL.
But I'm sure the constructor of ViewModel_Shared was hit TWICE while ActionA was called and ActionC was called.
So, basically, object(Item) was NEW twice.
I don't really understand why it's like that.
thank you all in advance!!!
public ActionResult actionA (ViewModel_Shared modelA)
{
return RedirectToAction("actionC", "controllerC", modelA);
}
public ActionResult actionB (ViewModel_Shared modelB)
{
return RedirectToAction("actionC", "controllerC", modelB);
}
public ActionResult actionC (ViewModel_Shared modelC)
{
modelC.FillEditedData();
// Send the data to view
ViewData.Model = modelC;
return View();
}
public class ViewModel_Shared
{
public ItemCustomer Item { get; set; }
public ViewModel_Shared()
{
Item = new ItemCustomer();
}
public void FillEditedData()
{
// NullReference exception was throw here, somehow, Item is null.
Item.LegalCost = "some value";
}
}
[Serializable]
public class ItemCustomer
{
public string Item_No { get; set; }
public string MaterialPricingGroup { get; set; }
public string MaterialGroup { get; set; }
public string Plant { get; set; }
public string LegalCost { get; set; }
}

As mentioned, complex objects cannot travel with requests.
Instead you need to serialize the object and pass the serialized data to the destination action method:
public ActionResult actionA (ViewModel_Shared modelA)
{
var serializedModel = JsonConvert.SerializeObject(modelA);
return RedirectToAction("actionC", "controllerC", serializedModel);
}
UPDATE
My bad. Indeed the parameters, sent through RedirectToAction() are sent as route values so even serialization cannot help here. At least not by itself - the routing must be setup appropriately ...
A different approach must be taken and during actionA, place your modelA into the TempData, then do redirect. In the actionC retrieve the model and carry on.
public ActionResult actionA (ViewModel_Shared modelA)
{
TempData["shared_model"] = modelA;
return RedirectToAction("actionC", "controllerC");
}
Later, in actionC:
public ActionResult actionC (ViewModel_Shared modelA)
{
var modelC = TempData["shared_model"];
modelC.FillEditedData();
ViewBag.Model = modelC;
return View();
}
Do note, that the objects in he TempData are alive only to the next request and then gone. Here you can read more about the TempData.

Yin
1) if you are using the ItemCustomer class as a property you should initialize it when you are using.
public ItemCustomer Item { get; set; }
2) if you are using ItemCustomer as object it will initialize when you constructor call as your example.
public ItemCustomer Item;
I have run the second point without get and set it's working fine.

using ViewBag to pass a model object

I'm trying to sort my result page (which is in another view than the filtration page). I have faced this weird issue I do not understand why keeps happening to me.
All the codes provided in very short form, please ask me if you need any other parts of my code for more information.
My Index view(where user filters results):
#model IEnumerable<Cars.Models.CarSearch>
#using (Html.BeginForm("SearchResult", "Home", FormMethod.Post,
new
{
id = "CategoryFormID",
data_modelListAction = #Url.Action("ModelList"),
data_makeListAction = #Url.Action("MakeList"),
data_editionListAction = #Url.Action("EditionList")
}))
{
<label>Make</label>
<select id="MakeID" name="carMake">
<option>All Makes</option>
</select>
}
My SearchResult view:
#model IEnumerable<Cars.Models.Car>
Make
My model:
public class Car
{
public String Make { get; set; } //is my table model
}
public class CarFilter {
public String carMake { get; set; }
}
public class CarSearch {
public CarFilter CarFilter { get; set; }
public byte PageSize { get; set; }
public short PageNumber { get; set; }
public int TotalRows { get; set; }
}
My Controller:
public ActionResult SearchResult(String sortOrder, CarFilter filters)
{
ViewBag.CurrentFilters = filters;
return View();
}
All I'm trying to do is to get carMake from Index post it to controller in CarFilter form (since in my code there are LOTS of fields in the form and I don't want to write them all down) and when user clicks on sort by Make it GET the SearchResult method and it's supposed to set filters = ViewBag.CurrentFilters which is the value user inputted from beginning.
Now the funny part is, when I replace CarFilter filters with String carMake and other places respectively. It works like a charm.
My question:
Why?
How can I do this with CarFilter filters?
UPDATE:
Problem is that filters = ViewBag.CurrentFilters in my SearchResult view does not work with the type CarFilter, because it keeps giving me NULL value when user clicked on the sort by Make.
Second UPDATE:
I tried changing filters = ViewBag.CurrentFilters with CarFilter = ViewBag.CurrentFilters. Now CarFilter filters in my SearchResult(...)method in my controller is not and null object, but ALL the values of the objects in the model class is null (which shouldn't be). I mean the filters object exists but it seems like the values of CarFilter class in my model haven't been passed by ViewBag.CurrentFilters to the view.

when you canged the name it worked because framework found property name and the bind it to what you have within action parameters doesnt work so nicely with objects. My advice is to stick with simple types
Here is similiar case:
How to send model object in Html.RenderAction (MVC3)
Its not a ViewBag problem thants how it works in general. Its the prime reason for using flatted models :/

ASP.NET MVC3: Displaying Validation Errors from Child View in Parent View

I'm trying to add a form to allow users to comment on posts on my blogging application. So far, I've added a form to the post details view and I can submit comments, adding them to my database correctly. However, I have a problem with displaying validation errors to the user. The comment form is contained within a partial view and is rendered using Html.RenderAction inside the post details view. I'd like to stress that I don't want to use AJAX for this as I'd like to approach this from a progressive enhancement point-of-view.
Here's the relevant posting action:
[HttpPost, Authorize]
public ActionResult AddComment(CommentViewModel newComment)
{
if (ModelState.IsValid)
{
Comment comment = new Comment(_userRepository.GetByUsername(User.Identity.Name));
Mapper.Map(newComment, comment);
_commentRepository.Add(comment);
_postsRepository.CommentAdded(comment.Article);
return RedirectToAction("Index", new { id = newComment.PostID });
}
// What do I do here?
}
I've tried several ways of returning views here but my issue is further complicated by some controller parameter validation that I have going on in the parent action:
//
// GET: /Posts/5/this-is-a-slug
public ActionResult Index(int id, string slug)
{
PostViewModel viewModel = new PostViewModel();
var model = _postsRepository.GetByID(id);
if (model != null)
{
if (slug == null || slug.CompareTo(model.Slug) != 0)
{
return RedirectToActionPermanent("Index", new { id, slug = model.Slug });
}
else
{
_postsRepository.PostVisited(model);
Mapper.Map(model, viewModel);
viewModel.AuthorName = _userRepository.GetById(model.AuthorID);
}
}
return View(viewModel);
}
This action basically mimics how SO's URLs work. If a post ID is supplied, the post is fetched from the database along with a slug which is created when the post is created. If the slug in the URL doesn't match the one in the database, it redirects to include the slug. This is working nicely but it does mean I'm having issues trying to populate my parent viewmodel, which is the following:
public class PostViewModel
{
public int PostID { get; set; }
public string Title { get; set; }
public string Body { get; set; }
public string Slug { get; set; }
public DateTime DatePublished { get; set; }
public int NumberOfComments { get; set; }
public int AuthorID { get; set; }
public string AuthorName { get; set; }
public List<CommentViewModel> Comments { get; set; }
public CommentViewModel NewComment { get; set; }
}
What I was hoping would work is to populate PostViewModel.NewComment, test to see if it has data and then using it to display any model errors. Unfortunately, I'm lost as to how to accomplish that. This question helped me shape my approach, but it didn't quite answer my problem.
Could someone give me a gentle push in the right direction? If my approach seems unreasonable, I'd love to find out why and what a potential fix would be.
Many thanks in advance.

Forgot to fill in my answer here. For anyone that happens to stumble on this, the answer was to use TempData to store the ModelState errors and then repopulating ModelState in the relevant controller action.
Firstly, I declared a key in the controller which would be used to reference the data inside TempData. I decided to base this on the CommentViewModel type as both actions depend on it.
public class PostsController : Controller
{
private static readonly string commentFormModelStateKey = typeof(CommentViewModel).FullName;
// Rest of class.
}
In this first action, the code checks to see if TempData contains data assigned to the key. If it does, it's copied into ModelState.
// GET: /posts/comment
[ChildActionOnly]
public PartialViewResult Comment(PostViewModel viewModel)
{
viewModel.NewComment = new CommentViewModel(viewModel.PostID, viewModel.Slug);
if (TempData.ContainsKey(commentFormModelStateKey))
{
ModelStateDictionary commentModelState = TempData[commentFormModelStateKey] as ModelStateDictionary;
foreach (KeyValuePair<string, ModelState> valuePair in commentModelState)
ModelState.Add(valuePair.Key, valuePair.Value);
}
return PartialView(viewModel.NewComment);
}
This action determines if the ModelState is valid before adding a comment to the database. If the ModelState is not valid, it is copied to TempData, which makes it available to the first action.
// POST: /posts/comment
[HttpPost, Authorize]
public ActionResult Comment(CommentViewModel newComment)
{
if (!ModelState.IsValid)
{
TempData.Add(commentFormModelStateKey, ModelState);
return Redirect(Url.ShowPost(newComment.PostID, newComment.Slug));
}
// Code to add a comment goes here.
}

How do I transfer ViewModel data between POST requests in ASP.NET MVC?

I have a ViewModel like so:
public class ProductEditModel
{
public string Name { get; set; }
public int CategoryId { get; set; }
public SelectList Categories { get; set; }
public ProductEditModel()
{
var categories = Database.GetCategories(); // made-up method
Categories = new SelectList(categories, "Key", "Value");
}
}
Then I have two controller methods that uses this model:
public ActionResult Create()
{
var model = new ProductEditModel();
return View(model);
}
[HttpPost]
public ActionResult Create(ProductEditModel model)
{
if (ModelState.IsValid)
{
// convert the model to the actual entity
var product = Mapper.Map(model, new Product());
Database.Save(product);
return View("Success");
}
else
{
return View(model); // this is where it fails
}
}
The first time the user goes to the Create view, they are presented with a list of categories. However, if they fail validation, the View is sent back to them, except this time the Categories property is null. This is understandable because the ModelBinder does not persist Categories if it wasn't in the POST request. My question is, what's the best way of keeping Categories persisted? I can do something like this:
[HttpPost]
public ActionResult Create(ProductEditModel model)
{
if (ModelState.IsValid)
{
// convert the model to the actual entity
var product = Mapper.Map(model, new Product());
Database.Save(product);
return View("Success");
}
else
{
// manually populate Categories again if validation failed
model.Categories = new SelectList(categories, "Key", "Value");
return View(model); // this is where it fails
}
}
But this is an ugly solution. How else can I persist it? I can't use a hidden field because it's a collection.

I would use the repository to fetch whatever data is needed and don't think it's an ugly solution:
[HttpPost]
public ActionResult Create(ProductEditModel model)
{
if (!ModelState.IsValid)
{
// manually populate Categories again if validation failed
model.Categories = Repository.GetCategories();
return View(model);
}
// convert the model to the actual entity
var product = Mapper.Map(model, new Product());
Database.Save(product);
// I would recommend you to redirect here
return RedirectToAction("Success");
}
To further refactor this I would recommend you watching the excellent Putting Your Controllers on a Diet video presentation by Jimmy Bogard.

I typically implement my lists (for drop downs) as a readonly property. When the View gets the value the property is self contained on what it needs to return the values.
public SelectList Categories
{
get
{
var categories = Database.GetCategories(); // made-up method
return new SelectList(categories, "Key", "Value");
}
}
If necessary you can grab the currently selected item (i.e. validation failed) from the property containing the id that was posted and bound to the instance of your class.

In my case I have a BaseModel class where I keep all those property list as class attributes.
Like in the following sample:
public IEnumerable<SelectListItem> CountryList
{
get
{
return GetCountryList().Select(
t => new SelectListItem { Text = t.Name, Value = Convert.ToString(t.CountryID) });
}
}
GetCountryList() is a function that ask a Singleton for data. This would only happen once in the app lifecycle
Another way for doing this, and if those lists are pretty big, would be to have a static utility class with the lookup table that returns the SelectListItem.
If you need to access a list that change from time to time then simply dont use a Singleton class.