OnModelCreating - 新创建的表保持为空

Question

我有两个表需要连接。在每个表中，分别插入数据。问题是，在将数据插入两个表之后，OnModelCreating方法中新创建的表仍然是空的吗？！

抱歉我的英文。

我在这里附上代码以便更好地理解：

Advertisement.cs

 public class Advertisement {
    [Key]
    public int AdvertisementID { get; set; }

    [Required]
    public DateTime CreateDate { get; set; }

    [Required MaxLength(256)]
    public string Title { get; set; }

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

    [Required]
    public int? TypeOfAd { get; set; }

    [Required]
    public bool IsTop { get; set; }

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

    public int Views { get; set; }

    [Required]
    public bool IsActive { get; set; }

    public int? SubcategoryID { get; set; }

    public virtual Subcategory Subcategory { get; set; }

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

    public virtual User User { get; set; }

    public virtual ICollection<Photo> Photos { get; set; }
}

Photo.cs

public class Photo {
    [Key]
    public int PhotoID { get; set; }

    [Required(MaxLength(512)]
    public string ImageUrl { get; set; }

    public string ThumbnailUrl { get; set; }

    public virtual ICollection<Advertisement> Advertisements { get; set; }
}

DbContext.cs

public class AdvertisingDbContext : DbContext {
    public AdvertisingDbContext() : base("Advertising") { }

    public DbSet<Advertisement> Advertisements { get; set; }
    public DbSet<Photo> Photos { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder) {
        modelBuilder.Entity<Advertisement>()
        .HasMany(x => x.Photos)
        .WithMany(y => y.Advertisements)
        .Map(m => {
            m.ToTable("AdvertisementPhotos");
            m.MapLeftKey("AdvertisementID");
            m.MapRightKey("PhotoID");
        });
    }
}