MusicStore 'System.Data.Objects.ObjectSet<....>' does not contain a definition for 'Add' and no extension method 'Add' accepting a first argument

Question

I'm following the MusicStore tutorial I'm already on the Part 8 of the tutorial. I got this error when I tried to add the ShoppingCart class.. I tried to google for a possible solution but failed to find a clean one T_T .. based on my research I'm getting this error because I'm using edmx which is database first instead of code first on the tutorial.

I had this codes added and is having an error on Add() and Remove()

namespace Project.Models 
{ 
    public partial class ShoppingCart 
    {  
        ProjectEntities db = new ProjectEntities();  

        string ShoppingCartId { get; set; }

        public const string CartSessionKey = "cart_ID";
        public static ShoppingCart GetCart(HttpContextBase context)
        {
            var cart = new ShoppingCart();
            cart.ShoppingCartId = cart.GetCartId(context);
            return cart;
        }
        // Helper method to simplify shopping cart calls
        public static ShoppingCart GetCart(Controller controller)
        {
            return GetCart(controller.HttpContext);
        }
        public void AddToCart(Product product)
        {
            // Get the matching cart and album instances
            var cartItem = db.Carts.SingleOrDefault(c => c.cart_ID == ShoppingCartId && c.product_ID == product.product_ID);

            if (cartItem == null)
            {
                // Create a new cart item if no cart item exists
                cartItem = new Cart
                {
                    product_ID = product.product_ID,
                    cart_ID = ShoppingCartId,
                    Count = 1,
                    DateCreated = DateTime.Now
                };
                db.Carts.Add(cartItem);
            }
            else
            {
                // If the item does exist in the cart,  then add one to the quantity
                cartItem.Count++;
            }
            // Save changes
            db.SaveChanges();
        }
        public int RemoveFromCart(int id)
        {
            // Get the cart
            var cartItem = db.Carts.Single(cart => cart.cart_ID == ShoppingCartId && cart.record_ID == id);

            int itemCount = 0;

            if (cartItem != null)
            {
                if (cartItem.Count > 1)
                {
                    cartItem.Count--;
                    itemCount = cartItem.Count;
                }
                else
                {
                    db.Carts.Remove(cartItem);
                }
                // Save changes
                db.SaveChanges();
            }
            return itemCount;
        }
        public void EmptyCart()
        {
            var cartItems = db.Carts.Where(cart => cart.cart_ID == ShoppingCartId);

            foreach (var cartItem in cartItems)
            {
                db.Carts.Remove(cartItem);
            }
            // Save changes
            db.SaveChanges();
        }
        public List<Cart> GetCartItems()
        {
            return db.Carts.Where(cart => cart.cart_ID == ShoppingCartId).ToList();
        }
        public int GetCount()
        {
            // Get the count of each item in the cart and sum them up
            int? count = (from cartItems in db.Carts
                          where cartItems.cart_ID == ShoppingCartId
                          select (int?)cartItems.Count).Sum();
            // Return 0 if all entries are null
            return count ?? 0;
        }
        public decimal GetTotal()
        {
            // Multiply album price by count of that album to get 
            // the current price for each of those albums in the cart
            // sum all album price totals to get the cart total
            decimal? total = (from cartItems in db.Carts
                              where cartItems.cart_ID == ShoppingCartId
                              select (int?)cartItems.Count * cartItems.Product.Price).Sum();

            return total ?? decimal.Zero;
        }
        public int CreateOrder(Order order)
        {
            decimal orderTotal = 0;

            var cartItems = GetCartItems();
            // Iterate over the items in the cart, adding the order details for each
            foreach (var item in cartItems)
            {
                var orderDetail = new OrderDetail
                {
                    product_ID = item.product_ID,
                    order_ID = order.order_ID,
                    UnitPrice = item.Product.Price,
                    Quantity = item.Count
                };
                // Set the order total of the shopping cart
                orderTotal += (item.Count * item.Product.Price);

                db.OrderDetails.Add(orderDetail);

            }
            // Set the order's total to the orderTotal count
            order.Total = orderTotal;

            // Save the order
            db.SaveChanges();
            // Empty the shopping cart
            EmptyCart();
            // Return the OrderId as the confirmation number
            return order.order_ID;
        }
        // We're using HttpContextBase to allow access to cookies.
        public string GetCartId(HttpContextBase context)
        {
            if (context.Session[CartSessionKey] == null)
            {
                if (!string.IsNullOrWhiteSpace(context.User.Identity.Name))
                {
                    context.Session[CartSessionKey] = context.User.Identity.Name;
                }
                else
                {
                    // Generate a new random GUID using System.Guid class
                    Guid tempCartId = Guid.NewGuid();
                    // Send tempCartId back to client as a cookie
                    context.Session[CartSessionKey] = tempCartId.ToString();
                }
            }
            return context.Session[CartSessionKey].ToString();
        }
        // When a user has logged in, migrate their shopping cart to
        // be associated with their username
        public void MigrateCart(string userName)
        {
            var shoppingCart = db.Carts.Where(c => c.cart_ID == ShoppingCartId);
            foreach (Cart item in shoppingCart)
            {
                item.cart_ID = userName;
            }
            db.SaveChanges();
        }
    }
}  

I'm a starter in MVC and hopefully anyone would help me to resolve this.

Answer 1

OK here what I did guys to make it work.. instead of using .Add() I use .AddObject() and instead of using .Remove I use .DeleteObject().. I dont know the reason behind how this things work but atleast it doesn't show an error message anymore.. :P thanks for everyone who helped me.. :)