public class NorthwindContext : DbContext
{
     public NorthwindContext(DbContextOptions options):base(options) { }

     public NorthwindContext() { }

     protected override void OnModelCreating(ModelBuilder builder)
     {
         builder.Entity().HasKey(table => new {
         table.FriendId, table.UserId
         });
     }
     public DbSet Relationships { get; set; }
     public DbSet Users { get; set; }
}