ICollection 中的对象未与模型一起传递给视图

Question

我正在尝试创建一个网站，其中包含可以包含 cmets 的新闻。我一直在关注pluralsight.com 的指南，并且我已经按照信函指南中的内容进行了操作，但是当我在运行时调试并查看模型内部的内容时，不包括 cmets。

我的数据库类：

public class ProjectDB {
        public DbSet<ContentNode> ContentNodes{ get; set; }
        public DbSet<Comment> Comments { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {

            base.OnModelCreating(modelBuilder);

            modelBuilder.Entity<ContentNode>()
                .Property(n => n.ID).HasColumnName("NodeID");
            modelBuilder.Entity<ContentNode>()
                .HasMany(node => node.Comments)
                .WithRequired(comment => comment.Node);
        }
}

涉及的模型：

    public class ContentNode : Node
    {
        public ContentType ContentType { get; set; }
        public ContentCategory Category { get; set; }
        public ICollection<Comment> Comments { get; set; }

        public ContentNode()
        {
            Comments = new List<Comment>();
        }
    }

    public class Comment
    {
        public int ID { get; set; }
        public ContentNode Node { get; set; }
        public string Body { get; set; }
    }

从数据库中拉取新闻文章并发送到视图的控制器方法

[GET("frettir/{year}/{month}/{day}/{title}")]
public ActionResult GetArticle( int year, int month, int day, string title)
{
    var model = (from f in _db.ContentNodes
                 where f.dateCreated.Year == year &&
                       f.dateCreated.Month == month &&
                       f.dateCreated.Day == day &&
                       f.Title == title &&
                       f.ContentType.ID == 1
                 select f).Single();

    return View(model);
}

最后是视图本身：

@model Project.Models.ContentNode

@{
    ViewBag.Title = "GetByID";
}

<h2>GetByID</h2>

<fieldset>
    <legend>News</legend>

    <div class="display-label">
         @Html.DisplayNameFor(model => model.Title)
    </div>
    <div class="display-field">
        @Html.DisplayFor(model => model.Title)
    </div>

    <div class="display-label">
         @Html.DisplayNameFor(model => model.Body)
    </div>
    <div class="display-field">
        @Html.DisplayFor(model => model.Body)
    </div>

    <div class="display-label">
         @Html.DisplayNameFor(model => model.dateCreated)
    </div>
    <div class="display-field">
        @Html.DisplayFor(model => model.dateCreated)
    </div>
</fieldset>
<p>
    @Html.ActionLink("Edit", "Edit", new { id=Model.ID }) |
    @Html.ActionLink("Back to List", "Index")
</p>

    @foreach (var item in Model.Comments)
    {
        @Html.Partial("_Comment",item)
    }

@Html.ActionLink("New comment", "Create", "Comment", new { NodeID = Model.ID }, null)

我查看了示例，并且查看了视频指南十几次，看看我做错了什么。我想出的唯一解决方案是将 NodeContent 表与 Comments 表连接起来，并将其投影到另一个模型中，但据我所知，这不应该是必需的。

感谢任何帮助。

Answer 1

var model = _db.ContentNodes
    .Include(f => f.Comments) // eager load the child collection
    .Single(f => f.dateCreated.Year == year 
         && f.dateCreated.Month == month
         && f.dateCreated.Day == day 
         && f.Title == title 
         && f.ContentType.Id == 1);

Answer 2

这很可能是因为 Entity Framework 默认启用了延迟加载。您可以使用First 方法而不是Single 方法来显式强制查询运行：

var model = (from f in _db.ContentNodes
             where f.dateCreated.Year == year &&
                   f.dateCreated.Month == month &&
                   f.dateCreated.Day == day &&
                   f.Title == title &&
                   f.ContentType.ID == 1
             select f).First();
return View(model);