Problem 1.Products Shop

namespace ProductShop.Data
{
    using System;
    using System.Data.Entity;
    using System.Linq;

    using ProductShop.Models;

    public class ProductShopContext : DbContext
    {
        public ProductShopContext()
            : base("name=ProductShopContext")
        {
        }

        public virtual IDbSet<User> Users { get; set; }

        public virtual IDbSet<Category> Categories { get; set; }

        public virtual IDbSet<Product> Products { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Entity<User>().HasMany(u => u.Friends).WithMany().Map(
                m =>
                    {
                        m.MapLeftKey("UserId");
                        m.MapRightKey("FriendId");
                        m.ToTable("UserFriends");
                    });

            modelBuilder.Entity<User>()
                .HasMany(u => u.Products)
                .WithOptional(p => p.User).Map(m => { m.MapKey("BuyerId"); });

            modelBuilder.Entity<User>()
                .HasMany(u => u.Products)
                .WithRequired(p => p.User)
                .Map(m =>
                {
                    m.MapKey("SellerId");
                });

            base.OnModelCreating(modelBuilder);
        }
    }
}