非静态外键 EF 核心

Question

I am working on a messenger API, and it goning be something like discord which someone sends a friend request to another user, and if the user accepted, they start messaging. as you know each FriendRequest has two contacts, sender and receiver, there are two ways to implement this relationship, one way is to define a many-to-many relationship between FriendRequest and contact and limit the FriendRequest 's contacts to two. the other way is to define two properties in FriendRequest , SenderContact and ReceiverContact .

I chose the second way which each FriendRequest should have two foreign keys with two contacts. But EF added another foreign key automatically. I just want to know two things
1: Is the second way that I chose a good way? Is there any better way to implement this situation?
2: Can I prevent EF from creating the ContactId column?

OnModelCreating in MyConext:

protected override void OnModelCreating(ModelBuilder builder)
{
    builder.Entity<Contact>().HasMany<FriendRequest>().WithOne(f => f.FromContact);
    builder.Entity<Contact>().HasMany<FriendRequest>().WithOne(f => f.ToContact);
    base.OnModelCreating(builder);
}

FriendRequest:

public class FriendRequest
{
    public int Id { get; set; }
    public Contact FromContact { get; set; }
    public Contact ToContact { get; set; }
    public string Text { get; set; }
}

Contact:

public class Contact
{
    [Key]
    public int Id { get; set; }
    public int UserId { get; set; }
    public string Username { get; set; }
    public ICollection<Chat> Chats { get; set; }
    public ICollection<FriendRequest> FriendRequests { get; set; }
    public ICollection<Contact> Friends { get; set; }
}

Answer 1

Your approach seems okay to me, but you have a configuration error. Your contact object should be

public class Contact
{
    [Key]
    public int Id { get; set; }
    public int UserId { get; set; }
    public string Username { get; set; }
    public ICollection<Chat> Chats { get; set; }
    public ICollection<FriendRequest> SentFriendRequests { get; set; }
    public ICollection<FriendRequest> ReceivedFriendRequests { get; set; }
    public ICollection<Contact> Friends { get; set; }
}

FriendRequest can stay the same, tho it is recommended to define a foreign key

public class FriendRequest
{
    public int Id { get; set; }
    public Contact FromContact { get; set; }
    public Contact ToContact { get; set; }
    public string Text { get; set; }
}

And the configuration

    protected override void OnModelCreating(ModelBuilder builder)
    {
        builder.Entity<Contact>()
          .HasMany<FriendRequest>(c => c.SentFriendRequests)
          .WithOne(f => f.FromContact);

        builder.Entity<Contact>()
          .HasMany<FriendRequest>(c => c.ReceivedFriendRequests)
          .WithOne(f => f.ToContact);

        base.OnModelCreating(builder);
    }

I always take a second look at the MS documentation when configuring relations, I recommend you do that.