如何初始化我的模型 [重复]

Question

首先，我想向您展示我的模型。

public class Blog
{
    [Key]
    public int BlogID { get; set; }
    public System.Nullable <DateTime> LastModified { get; set; }
    public System.Nullable<int> AidID { get; set; }
    public virtual BlogAid BlogAid{ get; set; }
    public System.Nullable<int> AuthorID { get; set; }
    public virtual BlogAuthor BlogAuthor { get; set; }
    public System.Nullable<int> CommentID { get; set; }
    public virtual ICollection<BlogComment> BlogComment { get; set; }
    public System.Nullable<int> TitleID { get; set; }
    public virtual BlogTitle BlogTitle { get; set; }
    public System.Nullable<int> ContentID { get; set; }
    public virtual BlogContent BlogContent { get; set; }
    public System.Nullable<int> NewsID { get; set; }
    public virtual BlogNews BlogNews { get; set; }
}

尤其是这一行：

public virtual ICollection<BlogComment> BlogComment { get; set; }

这意味着我的博客和cmets之间是一对多的关系，那么看看我的控制器：

var comments = from c in DB.BlogCommenttbl
                      join b in DB.Blogtbl on c.BlogID equals b.BlogID
                      where c.CommentID > 0
                      select new
                      { Comments = c.Comments, LastModified=c.LastModifed};

if (comments.FirstOrDefault() !=null)
{
    bpm.Blogs.BlogComment = new List<BlogComment>();

    foreach (var item in comments.ToList())
    {
        bpm.Blogs.BlogComment.Add(new BlogComment{Comments=item.Comments, LastModifed=item.LastModified});
    }
}

视图是

@foreach (var item in Model.Blogs.BlogComment)
{
    <h3>Start Bootstrap <small>@Html.DisplayText(item.LastModifed.ToString())</small></h3>
    <p>@Html.DisplayText(item.Comments.ToString())</p>
}

但我收到了Object reference not set to an instance of an object. 错误。

然后我调试了代码，发现

bpm.Blogs.BlogComment = new List<BlogComment>();

无法正常工作，我该如何修复这个错误？或者处理这个问题？

Answer 1

您可能没有初始化bpm.Blogs 属性。在bpm.Blogs.BlogComment = new List<BlogComment>(); 行之前，您必须初始化Blogs：

bpm.Blogs = new Blog();

Answer 2

if (comments.FirstOrDefault() !=null)
{
    bpm.Blogs.BlogComment = new List<BlogComment>();

    foreach (var item in comments.ToList())
    {
        bpm.Blogs.BlogComment.Add(new BlogComment{Comments=item.Comments, LastModifed=item.LastModified});
    }
}

如果 cmets 不包含任何项目，则代码块将不会被执行。如果未执行，则不会实例化 bpm.Blogs.BlogComment。将其更改为：

bpm.Blogs.BlogComment = new List<BlogComment>();

if (comments.FirstOrDefault() !=null)
{
    foreach (var item in comments.ToList())
    {
        bpm.Blogs.BlogComment.Add(new BlogComment{Comments=item.Comments, LastModifed=item.LastModified});
    }
}