序列在ASP.NET MVC中包含多个元素

我想显示使用单个子类别名称的产品，但是我正在获取序列包含多个元素错误。

子类别名称传递值来显示产品控制器的操作，如下所示

 public ActionResult show(string subcategory)
        {
            if (subcategory == null)
            {
                return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
            }


            var subcat = db.SubCategories.Include("Products").Single(s => s.SubCategoryName == subcategory);

            if (subcat == null)
            {
                return HttpNotFound();
            }

            return View(subcat);
        }

我有这样的菜单视图，

@model IEnumerable<mTest.Models.Category>

<div>
    <ul>
            @foreach (var category in Model)
            {
                <li class="active has-sub"><a href="#"><span>@category.CategoryName</span></a>
                    <ul>
                        @foreach (var subcategory in category.SubCategories)
                        {
                            <li class="has-sub"><a href="/Products/[email protected]"><span>@subcategory.SubCategoryName</span></a></li>

                        }
                    </ul>

                </li>
            }
      </ul>
</div>

以及类别，子类别和产品型号，例如

public class Category
    {
        public Category()
        {
           Products = new HashSet<Product>();
           SubCategories = new HashSet<SubCategory>();
        }
        public int CategoryId { get; set; }

        public string CategoryName { get; set; }



        public virtual ICollection<SubCategory> SubCategories { get; set; }

        public virtual ICollection<Product> Products { get; set; }
    }

public class SubCategory
    {
        public SubCategory()
        {
            Products = new HashSet<Product>();
        }

        public int SubCategoryId { get; set; }
        public string SubCategoryName { get; set; }

        public int CategoryId { get; set; }

        public virtual Category Category { get; set; }
        public virtual ICollection<Product> Products { get; set; }

    }

public class Product
    {

        public int ProductId { get; set; }
        public string ProductName { get; set; }



        public int CategoryId { get; set; }

        public int SubCategoryId { get; set; }

        public virtual Category Category { get; set; }

        public virtual SubCategory SubCategory { get; set; }

    }

我有子类别的数据是这样的

|Computer=>HP
         =>Lenovo
|Computer=>HP
         =>Lenovo

|Mobile  =>Samsung
         =>Apple
|Mobile  =>Samsung
         =>Apple

如何解决这个问题。