Question
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?
Accepted Answer
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.
Popular Answer
It's not mandatory the second collection. You only need to left de .WithMany() empty like this:
modelBuilder.Entity<Friend>()
.HasOne(f => f.MainUser)
.WithMany()
.HasForeignKey(f => f.MainUserId);
modelBuilder.Entity<Friend>()
.HasOne(f => f.FriendUser)
.WithMany()
.HasForeignKey(f => f.FriendUserId);
look at this : https://github.com/aspnet/EntityFramework/issues/6052
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