Entity Framework 7 多对多连接表在插入时没有记录

Question

我正在尝试插入一个与其他表有多对多关系的表。表格如下：

ID 是主键并具有自动递增。我首先创建数据库，然后使用命令搭建/生成实体。我想在表

NOVEL

中插入一条记录，同时具有流派。这是我的插入代码：

public async Task<IActionResult> Create(CreateNovelViewModel novelVM)
        {
            Novel novel = new Novel();
            try
            {
                if (ModelState.IsValid)
                {
                    novel.NovelTitle = novelVM.NovelTitle;
                    novel.NovelCover = "";
                    novel.NovelDescription = novelVM.NovelDescription;
                    novel.AuthorId = novelVM.AuthorID;
                    novel.UserId = novelVM.UserID;

                    foreach(var genreId in novelVM.Genres)
                    {
                        var genre = new Genre();
                        novel.Genres.Add(genreId);
                    }

                    _context.Add(novel);
                    await _context.SaveChangesAsync();
                    return RedirectToAction(nameof(Index));
                }
                else
                {
                    ModelState.AddModelError("", "Không thể thêm.Hãy thử lại, nếu vấn đề còn tồn tại, liên hệ người có chuyên môn.");
                }
            }
            catch (RetryLimitExceededException ex)
            {
                ModelState.AddModelError("", "Không thể thêm. Hãy thử lại, nếu vấn đề còn tồn tại, liên hệ người có chuyên môn.");
            }
            ViewBag.AuthorId = new SelectList(_context.Authors, "AuthorId", "AuthorName", novelVM.AuthorID);
            ViewBag.UserId = new SelectList(_context.Users, "UserId", "UserId", novelVM.UserID);
            ViewBag.GenreId = new SelectList(_context.Genres, "GenreId", "GenreName");
            return View(novel);
        }

代码运行正常，一条记录添加到

NOVEL

成功。但是我不知道为什么

NOVEL_GENRE

表没有记录。我假设当时没有

novel

的 id，所以它不能插入到连接表中？

这是我的

Novel.cs

实体：

public partial class Novel
{
    [Key]
    public int NovelId { get; set; }

    public string NovelTitle { get; set; } = null!;

    public string NovelDescription { get; set; } = null!;

    public string NovelCover { get; set; } = null!;

    public DateTime NovelDatePost { get; set; } = DateTime.Now;

    public int NovelView { get; set; } = 1;

    public int AuthorId { get; set; }

    public string UserId { get; set; } = null!;

    public virtual Author Author { get; set; } = null!;

    public virtual ICollection<Chapter> Chapters { get; } = new List<Chapter>();

    public virtual User User { get; set; } = null!;

    public virtual ICollection<UserComment> UserComments { get; } = new List<UserComment>();

    public virtual ICollection<UserRating> UserRatings { get; } = new List<UserRating>();

    public virtual ICollection<Genre> Genres { get; } = new List<Genre>();
}

这是

Genre.cs

实体：

public partial class Genre
{
    public int GenreId { get; set; }

    public string GenreName { get; set; } = null!;

    public string GenreDescription { get; set; } = null!;

    public virtual ICollection<Novel> Novels { get; } = new List<Novel>();
}

我刚开始使用 EF，所以我可能会错误地使用该功能。如果有人为此举了一些例子，我们将不胜感激。谢谢。