实体框架4.1代码优先自我引用一对多和多对多关联

Question

我有一个用户可以收集他喜欢的用户...

另一个用户可以收集他喜欢的用户....

如果用户A喜欢用户B,并且用户B喜欢用户A,那么他们就会挂出.我需要向对方发送他们的联系信息.我们如何在Entity Framework Code First中代表这样的模型？

public class User
{
    public int UserId { get; set; }

    public int? UserLikeId { get; set; }
    public virtual UserLike UserLike { get; set; }
}

public class UserLike
{
    public int UserLikeId { get; set; }

    public int UserId { get; set; }
    public virtual User User { get; set; }

    public virtual ICollection<User> LikeUsers { get; set; }
}

这个型号是否正确？我不能让这个工作.

我尝试过另一种方式,但这也不行...

我试图将用户集合添加到用户表.

例如:

public virtual ICollection<User> userlike { get; set; }

public class User
{
    public int UserId { get; set; }
    public virtual ICollection<UserLike> UserLikes { get; set; }
}

public class UserLike
{
    public int UserLikeId { get; set; }

    public int UserId { get; set; }
    public virtual User User { get; set; }

    public int LikeUserId { get; set; }
    public virtual User LikeUser { get; set; }
}

当我尝试添加用户和他们喜欢的人时,我收到此错误:

已检测到与"UserLike_LikeUser"关系的"UserLike_LikeUser_Target"角色发生冲突的更改.

代表这种模型的最佳方式是什么？

Answer 1

你真的不需要一个单独的实体来描述这种关系,下面的对象模型可以解决这个问题:

public class User
{
    public int UserId { get; set; }
    public string Name { get; set; }

    public int? ThisUserLikesId { get; set; }
    public virtual User ThisUserLikes { get; set; }
    public virtual ICollection<User> LikeThisUser { get; set; }
}

public class Context : DbContext
{
    public DbSet<User> Users { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<User>()
                    .HasOptional(u => u.ThisUserLikes)
                    .WithMany(u => u.LikeThisUser)
                    .HasForeignKey(u => u.ThisUserLikesId);
    }
}

现在假设您手中有一个UserId,并希望找到喜欢此用户的其他用户,该用户也喜欢他:

using (var context = new Context())
{
    // For a given user id = 1
    var friends = (from u in context.Users
                   where u.UserId == 1
                   from v in u.LikeThisUser
                   where v.UserId == u.ThisUserLikesId
                   select new 
                   { 
                       OurUser = u, 
                       HerFriend = v 
                   })
                   .SingleOrDefault();

    ExchangeContactInfo(friends.OurUser, friends.HerFriend);
}                

更新1:

自引用多对多关联将使用连接表映射到数据库,该连接表需要不同的对象模型和完全流畅的API:

public class User
{
    public int UserId { get; set; }
    public string Name { get; set; }

    public virtual ICollection<User> ThisUserLikes { get; set; }
    public virtual ICollection<User> UsersLikeThisUser { get; set; }
}

public class Context : DbContext
{
    public DbSet<User> Users { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<User>()
                    .HasMany(u => u.ThisUserLikes)
                    .WithMany(u => u.UsersLikeThisUser)
                    .Map(c => 
                    {
                        c.MapLeftKey("UserId");
                        c.MapRightKey("OtherUserId");
                        c.ToTable("UserLikes");
                    });
    }
}

更新2:

正如我在这篇文章中解释的那样,多对多关联不能有有效载荷(例如EventId),如果是这种情况,那么我们必须将它分解为两个一对多关联到一个介入类,我可以看你已经正确地创建了这个类(UserLike)来表示附加到你自引用多对多关联的额外信息,但是这个中间类的关联不正确,因为我们需要准确定义2多对一从UserLike到User的关联,就像我在以下对象模型中展示的那样:

public class User
{        
    public int UserId { get; set; }
    public string Email { get; set; }       

    public virtual ICollection ThisUserLikes { get; set; }
    public virtual ICollection UsersLikeThisUser { get; set; }
}       

public class UserLike
{
    public int UserLikeId { get; set; }
    public int LikerId { get; set; }
    public int LikeeId { get; set; }
    public int EventId { get; set; }

    public User Liker { get; set; }
    public User Likee { get; set; }
    public virtual Event Event { get; set; }
}

public class Event
{
    public int EventId { get; set; }
    public string Name { get; set; }
}  

public class Context : DbContext 
{
    public DbSet Users { get; set; } 
    public DbSet Events { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity()
                    .HasMany(u => u.ThisUserLikes)
                    .WithRequired(ul => ul.Liker)
                    .HasForeignKey(ul => ul.LikerId);
        modelBuilder.Entity()                        
                    .HasMany(u => u.UsersLikeThisUser)
                    .WithRequired(ul => ul.Likee)
                    .HasForeignKey(ul => ul.LikeeId)
                    .WillCascadeOnDelete(false);
    }
}

现在,您可以使用以下LINQ查询来检索彼此喜欢的所有用户:

using (var context = new Context())
{                
    var friends = (from u1 in context.Users
                   from likers in u1.UsersLikeThisUser
                   from u2 in u1.ThisUserLikes 
                   where u2.LikeeId == likers.LikerId
                   select new
                   {
                       OurUser = u1.UserId,
                       HerFriend = u2.LikeeId 
                   })
                   .ToList();
}

希望这可以帮助.