Question

我想在博文中输出所有评论。我已成功输入数据库中的所有数据，我可以输出帖子。但是我无法输出评论。

我的帖子模型如下：

  public class Post
    {
        [Key]
        public int PostId { get; set; }
        public string Title { get; set; }
        public DateTime CreatedDate{get;set;}
        public DateTime UpdateDate { get; set; }
        public string Body { get; set; }
        public ICollection<Comment> Comments { get; set;}

    }

我的评论模型如下：

public int CommentId { get; set; }
public int PostId { get; set; }
[ForeignKey("PostId")]
public virtual Post Post{get; set;}
public string CommentCreateDate { get; set; }
public string CommentUpdateDate { get; set; }
public string CommeterName { get; set; }
public string EmailAddress { get; set; }
public string CommentText { get; set; }
public bool Approved { get; set; }

我的行动如下：

[HttpPost]
public ActionResult CreateComment(int ?id, CommentViewModel model)
{
    Post post = GetPost(id);
    var comment = new Comment();
    comment.Post = post;
    comment.CommentCreateDate = DateTime.Now.ToString();
    comment.CommeterName = model.Name;
    comment.EmailAddress = model.Email;
    comment.CommentText = model.Text;

    db.Comments.Add(comment);
    db.SaveChanges();

    m_commentList.Add(m_comment);

    ViewData["Comment"] = comment;
    ViewBag.Comment = comment;
    TempData["Comment"] = comment;

    return RedirectToAction("Index");

}

我的索引视图如下：

@using Blog.Models

@{


    ViewBag.Title = "Index";
    var viewDataComment = ViewData["Comment"] as Comment;
    var tempDataComment = TempData["Comment"] as Comment;


    bool isPreviousLinkVisible = ViewBag.IsPreviousLinkVisible ?? false;
    bool isNextLinkVisible = ViewBag.IsNextLinkVisible ?? false;
    bool isAdmin = ViewBag.IsAdmin ?? false;
}

@foreach (Post post in Model)
    {


        <div class="newsResult">

            <div class="title">@Html.DisplayFor(modelItem => post.Title)</div>
            <div class="updated"> <b>Created:</b> @Html.DisplayFor(modelItem => post.CreatedDate) </div>
            <div class="updated"> <b>Updated:</b> @Html.DisplayFor(modelItem => post.UpdateDate)</div>
            <div class="data"> <b></b>  @Html.DisplayFor(modelItem => post.Body)</div>


            @*<div class="data"> <b></b>  @Html.DisplayFor(x => tempDataComment.CommentText)</div>*@

            @foreach (Comment comment in  post.Comments.OrderBy(x => x.CommentCreateDate))  //Offending line
            {
                <div class="comment">
                    <div class="commentName">
                        @if (!string.IsNullOrWhiteSpace(comment.EmailAddress))
                        {
                            <a href="mailto: @comment.EmailAddress;">@comment.CommeterName</a>
                        }
                        else
                        {
                            @comment.CommeterName;
                        }
                    </div>
                    said:
                    <div class="commentBody">@Html.Raw(Html.Encode(comment.CommentText).Replace("\n", "<br/>"))</div>
                    <div class="commentTime">at @comment.CommentCreateDate.ToString() on @comment.CommentCreateDate.ToString()</div>
                </div>
            }

以上帖子显示没问题。但是，当我尝试访问评论时，它给了我一个例外（违规行是第二个foreach的开始）：

System.ArgumentNullException: Value cannot be null

我确定已经创建了数据并且包含var tempDataComment中可用的注释。

为什么会这样？有人可以帮忙吗？

提前谢谢！

Answer 1

通过添加无效检查来解决问题：

@if (post.Comments != null) //added this
            {
            foreach (Comment comment in post.Comments.OrderBy(x => x.CommentCreateDate))
            {

            <div class="comment">
                <div class="commentName">
                    @if (!string.IsNullOrWhiteSpace(comment.EmailAddress))
                    {
                        <a href="mailto: @comment.EmailAddress;">@comment.CommeterName</a>
                    }
                    else
                    {
                        @comment.CommeterName;
                    }
                </div>
                said:
                <div class="commentBody">@Html.Raw(Html.Encode(comment.CommentText).Replace("\n", "<br/>"))</div>
                <div class="commentTime">at @comment.CommentCreateDate.ToString() on @comment.CommentCreateDate.ToString()</div>
            </div>
            }
       }

无法输出帖子中的所有评论

1 个答案: