EF Core - 类上的多对多关系

问题描述

我找到了答案

实体框架核心:多对多与同一实体的关系并像这样尝试.

实体:

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

    public virtual ICollection<Friend> Friends { get; set; }
}

public class Friend
{
    public int MainUserId { get; set; }

    public User ManUser { get; set; }

    public int FriendUserId { get; set; }

    public User FriendUser { get; set; }
}

流畅的 API:

modelBuilder.Entity<Friend>()
    .HasKey(f => new { f.MainUserId, f.FriendUserId });

modelBuilder.Entity<Friend>()
    .HasOne(f => f.ManUser)
    .WithMany(mu => mu.Friends)
    .HasForeignKey(f => f.MainUserId);

modelBuilder.Entity<Friend>()
    .HasOne(f => f.FriendUser)
    .WithMany(mu => mu.Friends)
    .HasForeignKey(f => f.FriendUserId);

当我添加迁移时，错误信息是

无法在User.Friends"和Friend.FriendUser"之间创建关系，因为User.Friends"和Friend.ManUser"之间已经存在关系.导航属性只能参与一个关系.

When I Add-Migration, the error message is

Cannot create a relationship between 'User.Friends' and 'Friend.FriendUser', because there already is a relationship between 'User.Friends' and 'Friend.ManUser'.Navigation properties can only participate in a single relationship.

我该怎么办?或者我应该创建一个实体 FriendEntity:User?

What should I do? Or I should create an Entity FriendEntity:User?

推荐答案

问题是你不能让一个集合同时支持一对多的关联.Friend 有两个外键，它们都需要在它们引用的实体中有一个反向.所以添加另一个集合作为 MainUser 的反面:

The problem is that you can't have one collection to support both one-to-many associations. Friend has two foreign keys that both need an inverse end in the entity they refer to. So add another collection as inverse end of MainUser:

public class User
{
    public int UserId { get; set; }
    public virtual ICollection<Friend> MainUserFriends { get; set; }
    public virtual ICollection<Friend> Friends { get; set; }
}

和映射:

modelBuilder.Entity<Friend>()
    .HasKey(f => new { f.MainUserId, f.FriendUserId });

modelBuilder.Entity<Friend>()
    .HasOne(f => f.MainUser)
    .WithMany(mu => mu.MainUserFriends)
    .HasForeignKey(f => f.MainUserId).OnDelete(DeleteBehavior.Restrict);

modelBuilder.Entity<Friend>()
    .HasOne(f => f.FriendUser)
    .WithMany(mu => mu.Friends)
    .HasForeignKey(f => f.FriendUserId);

其中一个(或两个)关系应该没有级联删除，以防止多个级联路径.

One (or both) of the relationships should be without cascading delete to prevent multiple cascade paths.

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