使用两个FK时无法创建关系 [英] Cannot create a relationship when using two FK

问题描述

我在我的 ASP.Net Core 应用程序中使用 EF ，并且尝试将 UserNotification 表添加到我的 User 表中。这些是表结构：

I'm using EF in my ASP.Net Core application and I'm trying to associate an UserNotification table to my User table. These are the tables structure:

public class User : IdentityUser
{
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public virtual UserNotifications { get; set; }
}

public class UserNotifications
{
    public int Id { get; set; }

    [Key, ForeignKey("User")]
    public string UserId { get; set; }
    public User User { get; set; }

    [Key, ForeignKey("Sender")]
    public string SenderId { get; set; }
    public virtual User Sender { get; set; }      

    public string Title { get; set; }
    public string Message { get; set; }
}

我所做的就是创建 ForeignKey UserNotifications 中的code>，我将存储 User 已收到的所有通知。

What I did is create a ForeignKey of UserNotifications which I'm going to store all the notifications that the User has reiceved.

在表 UserNotifications 内，我创建了两个 FK 用户和发件人。本质上，我想存储已收到通知的 User 的 Id 和 Id已发送通知的用户的（发件人）。

Inside the table UserNotifications I created two FK for User and Sender. Essentially I want store the Id of the User that has reiceved the notification, and the Id of the User that has sent the notification (Sender).

在 OnModelCreating 内，我还定义了以下逻辑：

Inside the OnModelCreating I also defined the following logic:

builder.Entity<UserNotifications>(entity =>
{
    entity.HasKey(n => n.Id);
    entity.HasOne(u => u.User)
          .WithOne(u => u.UserNotifications)
          .HasForeignKey<User>(u => u.Id);

    entity.HasOne(u => u.Sender)
          .WithOne(u => u.UserNotifications)
          .HasForeignKey<User>(u => u.Id);
 });

当我在控制台：

add-migration InitialMigration -context MyAppContext

我得到：

无法在'User.UserNotifications'和'UserNotifications之间建立关系.Sender，因为 UserNotifications.User和 User.UserNotifications之间已经存在关系。导航属性只能参与单个关系。

Cannot create a relationship between 'User.UserNotifications' and 'UserNotifications.Sender', because there already is a relationship between 'UserNotifications.User' and 'User.UserNotifications'. Navigation properties can only participate in a single relationship.

我是 EntityFramework ，所以我不知道该如何解决，有人可以解释我做错了吗？

I'm a newbie of EntityFramework so I don't know how to fix this, someone could explain what I did wrong?

在此先感谢您的帮助。

推荐答案

您所描述的模型表示用户之间的两个一对多关系和 UserNotifications （顺便说一下，该实体应命名为 UserNotification ）实体。每个EF关系可以在每一侧映射到0或1个唯一的导航属性。

The model you are describing represents two one-to-many relationships between the User and UserNotifications (btw, the entity should be named UserNotification) entities. Each EF relationship can be mapped to 0 or 1 unique navigation properties at each side.

您已经有两个 User 和发件人在 UserNotifications 中引用导航属性（和相应的FK）。您需要的是 User 中的两个对应的集合导航属性：

You already have two User and Sender reference navigation properties (and corresponding FKs) in UserNotifications. What you need is two corresponding collection navigation properties in User:

public class User : IdentityUser
{
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public virtual ICollection<UserNotifications> ReceivedNotifications { get; set; }
    public virtual ICollection<UserNotifications> SentNotifications { get; set; }
}

并使用流畅的API进行映射：

and map the with fluent API:

builder.Entity<UserNotifications>(entity =>
{
    entity.HasKey(n => n.Id);

    entity.HasOne(n => u.User)
        .WithMany(u => u.ReceivedNotifications)
        .HasForeignKey(n => u.UserId)
        .IsRequired()
        .OnDelete(DeleteBehavior.Delete);

    entity.HasOne(n => n.Sender)
        .WithMany(u => u.SentNotifications)
        .HasForeignKey(n => n.SenderId)
        .IsRequired()
        .OnDelete(DeleteBehavior.Restrict);
 });

请注意，由于该模型引入了所谓的多个级联路径，需要关闭至少一个层叠删除并手动进行处理。

Note that since such model introduces the so called multiple cascade paths, you need to turn at least one of the cascade delete off and handle it manually.

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