实体框架定义复杂的对象关系

Question

我有一个 User 和 Following 类定义如下：

public class User : IdentityUser
{
    public User()
    {
        Followers = new HashSet<Following>();
        Following = new HashSet<Following>();
    }

    [Key]
    public string ID { get; set; }
...
...

    public virtual ICollection<Following> Followers { get; set; }

    public virtual ICollection<Following> Following { get; set; } 
}

public class Following
{
        [Key]        
        public int ID {get;set;}

        [MaxLength(100)]
        public string follower { get; set; }

        [MaxLength(100)]
        public string following { get; set; }           

        public virtual User UserFollower { get; set; }

        public virtual User UserFollowing { get; set; }
 }

Following中的属性follower和following都是User对象的外键，代表关系。然后在 DBcontext 类中，我将覆盖 OnModelCreating：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {      
        modelBuilder.Entity<User>()
            .HasMany<Following>(u => u.Followers)
            .WithOptional()
            .HasForeignKey(c => c.following);

        modelBuilder.Entity<User>()
            .HasMany<Following>(u => u.Following)
            .WithOptional()
            .HasForeignKey(c => c.follower);
}

这非常适合获取用户的关注者和关注者：

User user = await UserManager.FindByIdAsync(ID);
List<Following> followers = user.Following.ToList();

我的基本问题是如何创建 UserFollower 和 UserFollowing 关系，以便将 Following 的这些属性中的每一个都映射到用户？

理想情况下，我可以按照以下方式做一些事情：

User user = await UserManager.FindByIdAsync(ID);
List<Following> followers = user.Following.ToList();

User userFollowing = followers[0].UserFollowing;

Answer 1

稍微修改你的模型

public class User : IdentityUser
{
    public User()
    {
        // Don't do this. Entity Framwork will do that for you
        // Followers = new HashSet<Following>();
        // Following = new HashSet<Following>();
    }

    // Don't add this. IdentityUser has already defined it as `Id`
    // [Key]
    // public string ID { get; set; }

    public virtual ICollection<Following> Followers { get; set; }

    public virtual ICollection<Following> Following { get; set; } 
}

public class Following
{
    [Key]        
    public int ID {get;set;}

    // [MaxLength(100)] No need to do this as this is Foreign Key Property
    public string follower { get; set; }

    // [MaxLength(100)] No need to do this as this is Foreign Key Property
    public string following { get; set; }           

    public virtual User UserFollower { get; set; }

    public virtual User UserFollowing { get; set; }
}

然后是用户流畅的 API 来定义关系

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{      
    modelBuilder.Entity<User>()
        .HasMany(u => u.Followers)
        .WithRequired(f => f.UserFollower)
        .HasForeignKey(c => c.following);

    modelBuilder.Entity<User>()
        .HasMany(u => u.Following)
        .WithRequired(f => f.UserFollowing)
        .HasForeignKey(c => c.follower);
}

这将创建一个双向关系。进一步的 EntityFramework 将覆盖所有虚拟属性并定义您期望的行为。

如果您没有修改 EntityFramework 配置，您将可以直接这样做

User user = await UserManager.FindByIdAsync(ID);
List<Following> followers = user.Following.ToList();

User userFollowing = followers[0].UserFollowing;