C# 如何使用实体框架计算数据库中的嵌套集合

我正在制作我的第一个Asp.NETMVC应用程序-论坛系统。 我试图显示子类别中有多少帖子和线程

这是我的桌子：

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; }
}

但这给了我所有线程和帖子的数量，而不是每个子类别的具体数量。

---

提前感谢。

我相信您正在寻找的是：

var model = this.Data
    .Categories
    .Select(c => new IndexCategoryViewModel
    {
        Name = c.Name,
        SubCategories = c.SubCategories,
        ThreadsCount = c.Threads.Count(),
        PostsCount = c.Threads.Sum(t => t.Posts.Count()),
    })
    .ToList();

在这里，您可以创建嵌套查询来统计每个类别的线程和帖子。您不需要

threadscont

和

postscont

，因为它们存储总计数，而不是每个类别的计数

注意

我假设

Threads

属性存在于category类上，而

Posts

属性存在于thread类上。否则，您将需要使用谓词将POST与线程关联，并将线程与类别关联。最常见的是ID，在这种情况下，代码看起来类似于：

var model = this.Data
    .Categories
    .Select(c => new IndexCategoryViewModel
    {
        Name = c.Name,
        SubCategories = c.SubCategories,
        ThreadsCount = this.Data
            .Threads
            .Count(t => t.CategoryId == c.Id),
        PostsCount = this.Data
            .Posts
            .Count(p => this.Data
                .Threads
                .Any(t => p.ThreadId == t.Id && t.CategoryId == c.Id)
            ),
    })
    .ToList();

---

请注意，我还跳过了所有

.all（）

调用，因为它们看起来是多余的，尽管我不确定它们是做什么的，所以如果需要，您可以将其扔回那里。

试试这个，您还需要更改ViewModel以反映需求

public ActionResult Index()
{
    var model = from subCategory in this.Data.SubCategories
                select new SubCategoryViewModel
                {
                    Name = subCategory.Category.Name,
                    SubCategory = subCategory,
                    ThreadsCount = subCategory.Threads.Count(),
                    PostsCount = subCategory.Threads.SelectMany(c => c.Posts).Count(),
                })
                .ToList();


    return this.View(model);
}

---

创建表示要显示内容的视图模型

public class SubCategoryVM
{
  public string Title { get; set; }
  public string Description { get; set; }
  public int ThreadsCount { get; set; }
  public int PostCount { get; set; }
}

public class CategoryVM
{
  public string Name { get; set; }
  public List<SubCategoryVM> SubCategories { get; set; }
}

看法

@model IEnumerable
@{
ViewBag.Title=“主页”；
}
@foreach（模型中的var类别）
{
@类别.名称
@foreach（类别中的var子类别。子类别）
{
//在你看来，下面这句话毫无意义
// 
//假设您在SubCategory Controller中有方法：public ActionResult Details（字符串标题），那么
@ActionLink（subCategory.Title，“详细信息”，“子类别”，新{Title=subCategory.Title}，null）
@子类别.说明

@子类别.ThreadCountthreads

@subCategory.PostCountposts

}
}

这就是整个视图吗？如果是这样，则需要创建一个表示要显示内容的视图模型。特别是，CategoryViewModel应该包含线程计数和posts计数的属性，并且您是否真的有一个名为

子类别的控制器，它对每个子类别标题都有一个方法（
）！
public ActionResult Index()
{
    var model = from subCategory in this.Data.SubCategories
                select new SubCategoryViewModel
                {
                    Name = subCategory.Category.Name,
                    SubCategory = subCategory,
                    ThreadsCount = subCategory.Threads.Count(),
                    PostsCount = subCategory.Threads.SelectMany(c => c.Posts).Count(),
                })
                .ToList();


    return this.View(model);
}

public class SubCategoryVM
{
  public string Title { get; set; }
  public string Description { get; set; }
  public int ThreadsCount { get; set; }
  public int PostCount { get; set; }
}

public class CategoryVM
{
  public string Name { get; set; }
  public List<SubCategoryVM> SubCategories { get; set; }
}

public ActionResult Index()
{
  var model = this.Data.Categories.Select(c => new CategoryVM
  {
    Name = c.Name,
    SubCategories = c.SubCategories.Select(s => new SubCategoryVM
    {
      Title = s.Title,
      Description = s.Description,
      ThreadsCount = s.Threads.Count,
      PostsCount = s.Threads.SelectMany(t => t.Posts).Count;
    })
  });
  return View(model);
}

@model IEnumerable<CategoryVM>
@{
  ViewBag.Title = "Home Page";
}

<div class="container">
  @foreach (var category in Model)
  {
    <div class="row">
      <h5>@category.Name</h5>
      @foreach (var subCategory in category.SubCategories)
      {
        <div class="col-md-10">
          <div class="row">
            <h7>
              // The following line in your view makes no sense
              // <a href="/SubCategory/@subCat.Title">@subCat.Title</a>
              // Assuming you have method: public ActionResult Details(string title) in SubCategoryController, then
              @Html.ActionLink(subCategory.Title, "Details", "SubCategory", new { title = subCategory.Title }, null)
            </h7>
          </div>
          <div class="row">
            <p>@subCategory.Description</p>
          </div>
        </div>
        <div class="col-md-2">
          <p><span>@subCategory.ThreadCount</span><span>threads</span></p>
          <p><span>@subCategory.PostCount</span><span>posts</span></p>
        </div>
      }
    </div>
  }
</div>