Mixing local list operations with linq to entities database operations - asp.net-mvc

Question

I have 2 lists. A shopping cart list, which contains a objects with the properties; Quantity and ProductId. I then get all products from the repository (IQueryable) that has ProductId in the shopping cart list. This means that for every product, there is a shopping cart object with the Quantity related to it.
When doing the select, I want to assign this Quantity also, but the only way I know to do this is to query the cart again.
For egx.
model = (from p in productService.GetAllProducts()
where cart.Entries.Select(c => c.ProductId).Contains(p.ProductId)
select new CartViewItem
{
Price = p.Price,
ProductId = p.ProductId,
ProductName = p.ProductName,
Quantity = cart.Entries.FirstOrDefault(c => c.ProductId == p.ProductId).Quantity
}).ToList();
Model:
public class ShoppingCartEntry
{
public int ProductId { get; set; }
public int Quantity { get; set; }
}
cart.Entries is not coming from a repository. productService.GetAllProducts() returns an entityframework's IQueryable.
EDIT: My new code is:
model= (from p in productService.GetAllProducts()
from c in cart.Entries
where c.ProductId == p.ProductId
select new CartViewItem
{
Price = p.Price,
ProductId = p.ProductId,
ProductName = p.ProductName,
Quantity = c.Quantity
}).ToList();
This throws an error:
Unable to create a constant value of type 'SampleApp.WebUI.Models.ShoppingCartEntry'. Only primitive types ('such as Int32, String, and Guid') are supported in this context.

Answer 1

i think this should work...
var model = (from c in cart.Entires // The small local cart collection
let cpid = cart.Entires.Select(c2 => c2.ProjectId) //
from p in productService.GetAllProducts() // Query all Products used in cart
.Where(queryp => cpid.Contains(queryp.ProjectId)).ToList()
where p.ProductId == c.ProductId
select new CartViewItem {
p.Price,
p.ProductId,
p.Brand,
p.ProductName,
Discount = p.DiscountPercent * c.Quantity}).ToList();