Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
579 views
in Technique[技术] by (71.8m points)

c# - EF Core - Many to many relationship on a class

User-Friend relationship

I find an answer

Entity Framework Core: many-to-many relationship with same entity and try like this.

Entitys:

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; }
}

The fluent 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);

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.

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

See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Reply

0 votes
by (71.8m points)

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; }
}

And the mapping:

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);

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


与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
OGeek|极客中国-欢迎来到极客的世界,一个免费开放的程序员编程交流平台!开放,进步,分享!让技术改变生活,让极客改变未来! Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

...