Implement a collection of an object in my view model - ASP.net MVC

Question

I'm Completely new in ASP.net MVC

I have two model first is category

public class Category
{
    public virtual int Id { get; set; }
    [Required]
    public virtual string CategoryName { get; set; }
    public virtual List<SubCategory> SubCategories { get; set; }

}

and next subcategory model:

public class SubCategory
{
    public virtual int Id { get; set; }

    public virtual int CategoryId { get; set; }
    [Required]
    public virtual string SubCategoryName { get; set; }
    public virtual Category Category { get; set; }
    public virtual List<Question> Questions { get; set; }

}

I need to have a list of my categories and also a list of subcategories both in my view so this is my view model

public class CategorySubCategoryViewMoel
{
    public ICollection<Category> Category { get; set; }
    public SubCategory SubCategory { get; set; }


}

and here is my view

@model FinalSearch5.Models.CategorySubCategoryViewMoel
 <ul>
   @foreach (var category in Model.Category)
   {
     <li>@category.CategoryName</li>
   }
 </ul>

here is my controller

    public ActionResult Index()
    {
        var cats = db.Categories.ToList();
        return View(cats);
    }

It's not implementing completely yet but until here there is an Error

The model item passed into the dictionary is of type 'System.Collections.Generic.List1[FinalSearch5.Models.Category], but this dictionary requires a model item of type 'FinalSearch5.Models.CategorySubCategoryViewMoel'.`

Appreciate if help me what is the problem thank you.

The error message is self explanatory (your view expects CategorySubCategoryViewMoel but your passing it List<Category> But Category contains a collection of SubCategory so why do you need a view model with 2 separate collections - surely you would want to display each category, and for each category, its collection of SubCategory (i.e. nested foreach loops) — user3559349
– user3559349, Commented Jul 24, 2016 at 9:05
You don't necessarily need a view model if the view is for display only (although its still good practice to use one). The view can be @model List<Category) and then @foreach(var category in Model) { @foreach(var subCategory in category) { ... — user3559349
– user3559349, Commented Jul 24, 2016 at 9:14
By display only, I meant that you are not editing properties of Category or SubCategory in the view (in which case a foreach loop would never have worked anyway). — user3559349
– user3559349, Commented Jul 24, 2016 at 9:46
And that should have read @foreach(var subCategory in category.SubCategories) { — user3559349
– user3559349, Commented Jul 24, 2016 at 9:47

user3559349 · Accepted Answer · 2016-07-24 10:19:27Z

You view expects a model which is typeof CategorySubCategoryViewMoel but in the Index() method, you return a model which is List<Category>. In order for it to work, you could change the method to

public ActionResult Index()
{
    var model = new CategorySubCategoryViewMoel
    {
        Category = db.Categories.ToList()
    }
    return View(model );
}

Note that the property is a collection, so its name should be pluralized, and need only be IEnumerable i.e. public IEnumerable<Category> Categories { get; set; }

However its unclear what the purpose of your view model is. Its only other property is public SubCategory SubCategory { get; set; } and you never assign a value to it, or use it in the view. You code could use your current Index() method and then the view would be

@model List<Category>
<ul>
    @foreach(var category in Model)
    {
        <li>
            @category.CategoryName
            <ul>
                @foreach(var subCategory in category.SubCategories)
                {
                    <li>@subCategory.SubCategoryName</li>
                }
            </ul>
        <li>
    }
<ul>

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