如何使用实体框架对数据库中的嵌套集合进行计数

我正在制作我的第一个Asp.net Mvc应用程序-论坛系统。我正在尝试显示子类别中有多少帖子和主题。

这是我的表：

public class Category
{
   private ICollection<SubCategory> subCategories;

   public Category()
   {
       this.subCategories = new HashSet<SubCategory>();
   }

   public int Id { get; set; }

   public string Name { get; set; }

   public virtual ICollection<SubCategory> SubCategories
   {
       get { return this.subCategories; }
       set { this.subCategories = value; }
   }                          
}


public class SubCategory
{
    private ICollection<Thread> threads;

    public SubCategory()
    {
        this.threads = new HashSet<Thread>();
    }

    public int Id { get; set; }

    public string Title { get; set; }

    public string Description { get; set; }

    public int CategoryId { get; set; }

    public virtual Category Category { get; set; }

    public virtual ICollection<Thread> Threads
    {
        get { return this.threads; }
        set { this.threads = value; }
    }
}


public class Thread
{
    private ICollection<Post> posts;

    public Thread()
    {
        this.posts = new HashSet<Post>();
    }

    public int Id { get; set; }

    public string Title { get; set; }

    public virtual SubCategory SubCategory { get; set; }

    public int SubCategoryId { get; set; }

    public virtual ICollection<Post> Posts
    {
        get { return this.posts; }
        set { this.posts = value; }
    }

    public string AuthorId { get; set; }

    public virtual ApplicationUser Author { get; set; } 
}


public class Post
{
    public int Id { get; set; }

    public string Content { get; set; }

    public int ThreadId { get; set; }

    public virtual Thread Thread { get; set; }

    public string AuthorId { get; set; }

    public virtual ApplicationUser Author { get; set; }
}

这是我的看法：

    @model IEnumerable<ForumSystem.Web.ViewModels.Home.IndexCategoryViewModel>
@{
    ViewBag.Title = "Home Page";
}

<div class="container">
    @foreach (var category in Model)
    {
        <div class="row">
            <h5>@category.Name</h5>

            @foreach (var subCat in category.SubCategories)
            {
                <div class="col-md-10">
                    <div class="row">
                        <h7>
                            <a href="/SubCategory/@subCat.Title">@subCat.Title</a>
                        </h7>
                    </div>
                    <div class="row">
                        <p>@subCat.Description</p>
                    </div>
                </div>
                <div class="col-md-2">
                        <p>@category.ThreadsCount threads</p>
                        <p>@category.PostsCount posts</p>
                    <div class="row">

                    </div>
                </div>
            }
        </div>
    }
</div>

@ category.ThreadsCount和PostsCount不起作用。我可以使用@ subCategory.Threads.Count轻松查看线程数，但无法获取帖子数。在控制器中，我尝试了很多事情。目前的代码是：

public ActionResult Index()
    {
        var threadScount = this.Data
                           .SubCategories
                           .All()
                           .SelectMany(x => x.Threads)
                           .Count();

        var postsCount = this.Data
                        .Threads
                        .All()
                        .SelectMany(x => x.Posts)
                        .Count();

        var model = this.Data
                    .Categories
                    .All()
                    .Select(c => new IndexCategoryViewModel
                    {
                        Name = x.Name,
                        SubCategories = c.SubCategories,
                        ThreadsCount = threadScount,
                        PostsCount = postsCount,
                    })
                    .ToList();


        return this.View(model);
    }

但这给了我所有线程和帖子数，而不是每个子类别都特定。提前致谢。