ASP.NET 5(MVC6)EF7外键可能会导致循环

public class Post
{

    [Key]
    public int PostId { get; set; }

    [Required]
    [MaxLength(140)]
    public string Title { get; set; }

    [Required]
    public string ApplicationUserId { get; set; }

    public ApplicationUser ApplicationUser { get; set; }
    public ICollection<Comment> Comments { get; set; }
}

public class Comment
{
    [Key]
    public int CommentId { get; set; }

    [Required]
    [StringLength(1000)]
    public string Text { get; set; }

    [Required]
    public int PostId { get; set; }

    [Required]
    public string ApplicationUserId { get; set; }


    public Post Post { get; set; }
    public ApplicationUser ApplicationUser { get; set; }

}

我收到错误：

Introducing FOREIGN KEY constraint ‘FK_Comment_Post_PostId’ on table ‘Comment’ may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION,or modify other FOREIGN KEY constraints.
Could not create constraint or index. See previous errors.

这正是它们在documents中展示的方式.

现在,如果我删除：

[Required]
public int PostId { get; set; }

并使用Fluent API如下：

builder.Entity<Comment>().HasOne(p => p.Post).WithMany(c => c.Comments).IsRequired();

我仍然得到同样的错误.如果我明确说明

builder.Entity<Comment>().HasOne(p => p.Post).WithMany(c => c.Comments).IsRequired().OnDelete(DeleteBehavior.Cascade);

我仍然得到同样的错误.

如果我使用以下内容：

builder.Entity<Comment>().HasOne(p => p.Post).WithMany(c => c.Comments);

可以在没有帖子的情况下输入评论.评论必须属于帖子.

我错过了什么吗？这是一个常见的用例,与PK所需的FK的1对多关系.