views for select list contained within a viewmodel and validation - asp.net-mvc-3

Question

My Scenario :
My Model is "Item" which contain 0 or many number of taxes (Model "Tax")
"Item" --> has 0 or n --> "Tax"
I have a View Model for MVC named "VMItem" which has an object of "Item", all taxes ("TaxDic") and selected taxes ("Taxes"). MVC page is bind to this view model ("ViewItem").
Requirement :
I want the MVC to display a list box of all taxes and enable user to select relevant tax for each item when he create the item.
Below is my code,
Reference to the following codes, ListBox which is for Taxes is not mandatory field. But when I submitted the form with some selection on ListBox, it shows red box around the ListBox and if I select nothing on ListBox and submit, there is no error it seems.
please have a look at the following scenario.. if there is any better way to achieve this, please someone guide me.
model
public class Item
{
[Display(Name="Item ID")]
public virtual Guid ItemID { get; set; }
[Required]
[Display(Name = "Name")]
public virtual string Name { get; set; }
[Required]
[Display(Name="Price")]
public virtual decimal Price { get; set; }
public virtual IEnumerable<Tax> Taxes { get; set; }
}
View Model
public class VMItem
{
public Item Item { get; set; }
public IEnumerable<Tax> Taxes { get; set; }
public IEnumerable<SelectListItem> TaxDic { get; set; }
}
Function to generate Select list item in the controller class
private VMItem GenerateViewModel(Item Item)
{
IEnumerable<Tax> Taxes = TaxServices.FindAll();
IList<SelectListItem> taxDic = new List<SelectListItem>();
// Generating Taxes and taxDic here..
VMItem VmItem = new VMItem
{
Item = Item,
Taxes = Taxes,
TaxDic = taxDic
};
return VmItem;
}
Contorller Action
// GET: /Product/Add
public ActionResult Add()
{
return View(GenerateViewModel(new Item()));
}
[HttpPost]
public ActionResult Add(VMItem collection)
{
Item item = new Item();
try
{
if(ModelState.IsValid)
{
item = collection.Item;
var taxes = collection.Taxes;
return View(GenerateViewModel(collection.Item));
}
// else..
}
// catch...
}
Views
<% using (Html.BeginForm()) { %>
<!-- more codes for other fields -->
<%: Html.ListBoxFor(model => model.Taxes, Model.TaxDic) %>
<!-- submit button goes below -->
<% } %>

Answer 1

This looks like a many-to-many relationship so first check if your tax class looks like this:
public class Tax
{
public Guid TaxId { get; set;}
public virtual ICollection<Item> Items { get; set;}
}
Then inside your OnModelCreating function in the context class add this:
modelBuilder.Entity<Item>()
.HasMany(i => i.Taxes).WithMany(t => t.Items)
.Map(t => t.MapLeftKey("ItemId")
.MapRightKey("TaxId")
.ToTable("ItemsTaxes"));
ViewModel
public class ItemTaxViewModel
{
public Item item { get; set; }
public virtual ICollection<AssignedTaxes> Taxes { get; set; }
}
public class AssignedTaxes
{
public int TaxId { get; set; }
public bool Assigned { get; set; }
}
Controller Action
public ActionResult Create()
{
var newItemVM = new ItemTaxViewModel
{
Item = new Item(),
Taxes = PopulateTaxes()
};
return View(newItemVM);
}
[HttpPost]
public ActionResult Create(ItemTaxViewModel itemTaxViewModel)
{
if(ModelState.IsValid)
{
var item = new Item();
item = itemTaxViewModel.Item;
AddOrUpdateTaxes(item, itemTaxViewModel.Taxes);
context.Items.Add(item);
context.SaveChanges();
return RedirectToAction("Index");
}
return View(itemTaxViewModel);
}
Helper Methods
private List<AssignedTaxes> PopulateTaxes()
{
var taxes = context.Taxes;
var assignedTaxes = new List<AssignedTaxes>();
foreach(var tax in taxes)
{
assignedTaxes.Add(new AssignedTaxes
{
TaxId = tax.TaxId,
Assigned = false
});
}
return assignedTaxes;
}
private void AddOrUpdateTaxes(Item item, ICollection<AssignedTaxes> assignedTaxes)
{
foreach(var assignedTax in assignedTaxes)
{
if(assignedTax.Assigned)
{
item.Taxes.Add(context.Taxes.Single(t => t.TaxId == assignedTax.TaxId));
}
}
}
EditorTemplate under the /Views/Shared/EditorTemplates
#model AssignedTaxes
#using projectName.ViewModels
<fieldset>
#Html.HiddenFor(model => model.TaxId)
#Html.CheckBoxFor(model => model.Assigned)
</fieldset>
View
<div class="editor-field">
#Html.EditorFor(model => model.Taxes)
<div class="editor-field">
Seems likes a lot of work but it's one of the cleanest ways to implement many-to-many checkboxes that I've come up with after going through many tutorials.

Answer 2

#Luis, your way looks well but it is too complicated and at the end you ended it with checkbox. May be it is better way. I came up with a solution and it was simple enough to me. I post it below. Please give me a feedback on it whether I should keep going with it or need improvement.
Controller
IEnumerable<Tax> Taxes = _TaxServices.FindTax();
IList<SelectListItem> taxDic = new List<SelectListItem>();
foreach (Tax tax in Taxes)
{
SelectListItem item = new SelectListItem();
item.Value = tax.TaxID.ToString();
item.Text = tax.Name;
taxDic.Add(item);
}
VMItem VmItem = new VMItem
{
Item = Item,
TaxDic = taxDic,
};
// Adding selected taxes to the list
IList<int> SelectedTaxes = new List<int>();
if (Item.Taxes != null && Item.Taxes.Count > 0)
{
foreach (Tax tax in Item.Taxes)
{
SelectedTaxes.Add(tax.TaxID);
}
}
VmItem.SelectedTax = SelectedTaxes;
return view(VmItem);
View
<%: Html.ListBoxFor(model => model.SelectedTax, Model.TaxDic) %>
Controller [HttpPost]
item.Taxes = new Iesi.Collections.Generic.HashedSet<Tax>();
if (vmItem.SelectedTax.Count() > 0)
{
IEnumerable<int> SelectedTaxesIDs = vmItem.SelectedTax.ToList();
foreach (int n in SelectedTaxesIDs)
{
item.Taxes.Add(_TaxServices.FindTax(n));
}
}
Please give feedback on this way.
Thanks.