ASP.Net MVC-正确执行MVVM

Question

I just have a quick question with regards to the MVVM design pattern... I'm just wondering if the way im doing things is the "correct" way?

I have a category mode like so:

[Table("Category")]
public class CategoryModel
{
    [Key]
    public Int32 CategoryId { get; set; }
    public string CategoryName { get; set; }
    public Int32? Category_ParentID { get; set; }
    public virtual CategoryModel Parent_Category { get; set; }
    public virtual ICollection<CategoryModel> SubCategories { get; set; }
    public Int16 CategoryOrder { get; set; }
    public bool Deleted { get; set; }

}

Not all of these are need on the "Create New Category" form, so I've created a ViewModel with just the required fields:

public class CategoryViewModel
{
    public string CategoryName { get; set; }           
    public Int32? Category_ParentID { get; set; }       
}

When a new category is being created, I send in the ViewModel as a parement, and create a new CategoryModel using the values from the ViewModel, like so:

if (ModelState.IsValid)
{

    CategoryModel newCategory = new CategoryModel()
    {
    CategoryName = model.CategoryName,
    Category_ParentID = model.Category_ParentID
    };

    //get the root node, and include it's subcategories
    var categoryList = DatabaseContext.Categories.Include("SubCategories").Single(c => c.CategoryId == model.Category_ParentID);

    //set the order of the category by getting the number of subcategories
    if (categoryList.SubCategories.Count > 0)
    newCategory.CategoryOrder = (Int16)(categoryList.SubCategories.Where(c => !c.Deleted).Max(c => c.CategoryOrder) + 1);
    else
    newCategory.CategoryOrder = 1;

    //save the new category
    DatabaseContext.Categories.Add(newCategory);
    await DatabaseContext.SaveChangesAsync();

    return PartialView("_CategoryModelItem", model);

} else {
    return new HttpStatusCodeResult(HttpStatusCode.InternalServerError);
}

Is this the right way to do the MVVM design pattern (ie the values are taken from a ViewModel, a new Model is created - takes values from the ViewModel - and gets written to the DB)? or am I misunderstanding how its suppored to be done?

Also

How does the "viewing" part work? What I mean is, if I'm listing a category and all of its subcategories in the Index() method of the Controller... should I used a model or viewmodel to display them? Of so, I'll need to add need to add the ICollection to the ViewModel, and then should I grab the data using Entity Framework and the Model class, and then somehow feed that into a ViewModel?

Answer 1

Yes, this is correct. But I'd make use of something like automapper to reduce the actual mapping code you need to write.

You'll use a viewmodel for displaying the items and it will be mapped from your model (again made easier with automapper).

You would also place your dataannotations on the viewmodel, and that will help with the validation logic on your view.

However, you don't need to use MVVM when you are doing MVC. They are different patterns that happen to be able to work together. MVVM is more commonly used in WPF application development.

Answer 2

Your are correct but i have some other tips for you:

• do not name Entity Framework entities with Model postfix, use the names of your DB tables in singular form
• always return a object. If you want to return a list of objects then wrap this list into a class. It will help you to keep your ViewModels more flexible and easy to extend. Use the wrapper class also if you want to return a single value. I call these objects PageModels.

If i want to return a single category then my edit page model will look like:

public class CategoryEditPageModel
{    
    CategoryModel Category { get; set;}
    //other data not directly related to category itself but needs to be visible on the page
    User CategoryOwner { get; set; }
}

Then POST only the CategoryModel if you want to update a category.