序列不包含元素：首先自引用代码 [英] Sequence contains no elements : self referencing code first

问题描述

当我尝试使用下一个实体进行自我引用

when I try to do self referencing with next entities

public class Folder
{
    public int Id { get; set; }
    public int?  ParentFolderId { get; set; } // Added property
    public string Name { get; set; }


    public virtual ICollection<Folder> Childrens { get; set; } // Added property
    public virtual ICollection<ArticleTitle> ArticleTitles { get; set; }

}


public class ArticleTitle
{
    public int Id { get; set; }
    public string Title { get; set; }
    public int? FolderId { get; set; }
    public virtual Folder Folder { get; set; }
    public virtual Article Article { get; set; }
}

我添加了几个属性（注释添加属性）和这行代码：

I added few properties (commented 'added property') and this line of code:

  modelBuilder.Entity<Folder>()
 .HasMany(s => s.Childrens)
 .WithOptional()
 .HasForeignKey(s => s.ParentFolderId);

得到这个例外：

< b>序列不包含元素

是否自动引用不正确？

推荐答案

这是你的代码如何：

public class Folder
{
    public int Id { get; set; }
    [ForeignKey("ParentFolder")]
    public int?  ParentFolderId { get; set; }
    public virtual Folder ParentFolder { get; set; }
    public string Name { get; set; }


    public virtual ICollection<Folder> Childrens { get; set; }
    public virtual ICollection<ArticleTitle> ArticleTitles { get; set; }

}
...

我很高兴它有帮助。

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