实体框架核心删除引用对象

Question

我有这个职位模型

public class Post
{
    [Key]
    public int Id { get; set; }
    public string AuthorId { get; set; }
    public ApplicationUser Author { get; set; }
    public int ChannelId { get; set; }
    [Required]
    public Channel Channel { get; set; }
    [Required]
    public string Text { get; set; }
    public int CountViewers { get; set; } 
    public List<ApplicationUser> WhoLiked { get; set; }
    public DateTime Date { get; set; } = DateTime.Now;
}

用户

public class ApplicationUser: IdentityUser
{
    [ProtectedPersonalData]      
    [MaxLength(70)]
    [MinLength(3)]
    [Required]
    public override string UserName { get; set; }
    [ProtectedPersonalData]
    [DataType(DataType.EmailAddress)]
    [Required]
    public override string Email { get; set; }
    [MaxLength(70)]
    public string FirstName { get; set; }
    [MaxLength(70)]
    [ProtectedPersonalData]
    public string LastName { get; set; }    
}

当我将用户添加到某些帖子的“喜欢的”列表中时，EF将该用户从其他列表中删除（在其他帖子中）。 我在做什么错了？

   post.WhoLiked.Add(user);
   _db.Posts.Update(post);
   await _db.SaveChangesAsync();