ViewBag multiple SelectList for dropdown list - asp.net-mvc-3

Question

I am trying to use dropdownList with two foreign keys which are modelId, and categoryId.
And I am using ViewBag with selectList.
public ActionResult Create()
{
ViewBag.categoryId = new SelectList(db.Category, "categoryId", "name");
ViewBag.modelId = new SelectList(db.Model, "modelId", "name");
return View();
}
//
// POST: /Product/Create
[HttpPost]
public ActionResult Create(Product product)
{
if (ModelState.IsValid)
{
db.Product.Add(product);
db.SaveChanges();
return RedirectToAction("Index");
}
ViewBag.categoryId = new SelectList(db.Category, "categoryId", "name", product.categoryId);
ViewBag.modelId = new SelectList(db.Model, "modelId", "name", product.modelId);
return View(product);
}
And here is my Create.cshtml.
<div class="editor-label">
#Html.LabelFor(model => model.Category)
</div>
<div class="editor-field">
#Html.DropDownList("categoryId", "--Select--")
</div>
<div class="editor-label">
#Html.LabelFor(model => model.Model)
</div>
<div class="editor-field">
#Html.DropDownList("modelId", "--Select--")
</div>
When I press submit button, error come up,
'An item with the same key has already been added'
What is problem? Is it problem with in Model?
Here is my models.
--Prodruct.cs--
public class Product
{
[Key] public int productId { get; set; }
[Required(ErrorMessage = "Please select category")]
public int categoryId { get; set; }
[Required(ErrorMessage = "Please select model")]
public int modelId { get; set; }
[DisplayName("Model name")]
public String model { get; set; }
public virtual Category Category { get; set; }
public virtual Model Model { get; set; }
}
--Category.cs--
public class Category
{
[Key] public int categoryId { get; set; }
public String name { get; set; }
}
--Model.cs--
public class Model
{
[Key] public int modelId { get; set; }
public String name { get; set; }
}
--RentalDB.cs--
public class rentalDB : DbContext
{
public DbSet<Product> Product { get; set; }
public DbSet<Model> Model { get; set; }
public DbSet<Customer> Customer { get; set; }
public DbSet<Order> Order { get; set; }
public DbSet<Cart> Cart { get; set; }
public DbSet<Category> Category { get; set; }
public DbSet<OrderDetails> OrderDetails { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
}
}
Where it is wrong? Index page in Create can get category data and model data. However, when I submit it, it has error, 'An item with the same key has already been added'.
Could you help me where has got problem?
Thank you.
--added more coding--
I am using this LINQ. Probably here has problem.
How can I add 'Model' entity in here?
var product = from a in db.Product.Include(a => a.Category)
select a;

Answer 1

This is how I would have done it..
I would suggest that you don't send your domain models to the view, but rather create a view model for each view. Doing it this way you will only include what is needed on the screen.
Create a new view model for your Create view:
public class ProductCreateViewModel
{
// Include other properties if needed, these are just for demo purposes
public string Name { get; set; }
public string SKU { get; set; }
public string LongDescription { get; set; }
// This is the unique identifier of your category,
// i.e. foreign key in your product table
public int CategoryId { get; set; }
// This is a list of all your categories populated from your category table
public IEnumerable<Category> Categories { get; set; }
// This is the unique identifier of your model,
// i.e. foreign key in your product table
public int ModelId { get; set; }
// This is a list of all your models populated from your model table
public IEnumerable<Model> Models { get; set; }
}
Category class:
public class Category
{
public int Id { get; set; }
public string Name { get; set; }
}
Model class:
public class Model
{
public int Id { get; set; }
public string Name { get; set; }
}
In your Create view you would have the following:
#model MyProject.ViewModels.ProductCreateViewModel
#using (Html.BeginForm())
{
<table>
<tr>
<td><b>Category:</b></td>
<td>
#Html.DropDownListFor(x => x.CategoryId,
new SelectList(Model.Categories, "Id", "Name", Model.CategoryId),
"-- Select --"
)
#Html.ValidationMessageFor(x => x.CategoryId)
</td>
</tr>
<tr>
<td><b>Model:</b></td>
<td>
#Html.DropDownListFor(x => x.ModelId,
new SelectList(Model.Models, "Id", "Name", Model.ModelId),
"-- Select --"
)
#Html.ValidationMessageFor(x => x.ModelId)
</td>
</tr>
</table>
<!-- Add other HTML controls if required and your submit button -->
}
Your Create action methods:
public ActionResult Create()
{
ProductCreateViewModel viewModel = new ProductCreateViewModel
{
// Here you do database calls to populate your dropdowns
Categories = categoryService.GetAllCategories(),
Models = modelService.GetAllModels()
};
return View(viewModel);
}
[HttpPost]
public ActionResult Create(ProductCreateViewModel viewModel)
{
// Check that viewModel is not null
if (!ModelState.IsValid)
{
viewModel.Categories = categoryService.GetAllCategories();
viewModel.Models = modelService.GetAllModels();
return View(viewModel);
}
// Mapping
Product product = ... // Do your mapping here
// Insert product in database
productService.Insert(product);
// Return the view where you need to be
}
I would also recommend that you use AutoMapper to do the mappings for you between your domain model and view model. I would also recommend that you look at Fluent Validation to take care of your view model validations.
I hope this helps.
UPDATED ANSWER
The service that was used to get all the categories could look like this:
public class CategoryService : ICategoryService
{
private readonly ICategoryRepository categoryRepository;
public CategoryService(ICategoryRepository categoryRepository)
{
// Check if category repository is not null, throw exception if it is
this.categoryRepository = categoryRepository;
}
public IEnumerable<Category> GetAllCategories()
{
return categoryRepository.GetAllCategories();
}
}
categoryRepository is injected by Autofac.
Category service interface:
public interface ICategoryService
{
IEnumerable<Category> GetAllCategories();
}
I currently still use Entity Framework 4.1 code first.
My category repository:
public class CategoryRepository : ICategoryRepository
{
MyContext db = new MyContext();
public IEnumerable<Category> GetAllCategories()
{
return db.Categories
.OrderBy(x => x.Name);
}
}
My category repository interface:
public interface ICategoryRepository
{
IEnumerable<Category> GetAllCategories()
}

Answer 2

public class Test
{
rentalDB db = new rentalDB();
public Product LoadProductById(int pId)
{
return db.Products.Include(p => p.Model).Include(p => p.Category).Where(p => p.productId == pId).SingleOrDefault();
} // To get specific product.
public IEnumerable<Product> LoadAllProducts()
{
return db.Products.Include(p => p.Model).Include(p => p.Category).ToList();
} // To get all products.
}
I have changed your DbSet to Products make it more clear. This is how you load all the references for one product or all products, in order to iterate over them.