var cartItem = _db.ShoppingCartItems.SingleOrDefault( c => c.CartId == ShoppingCartId

I have the following code from a tutorial and I'm trying to understand the following line of code. I added the full code lenght...

Just having a hard time understanding this sample code bellow...
var cartItem = _db.ShoppingCartItems.SingleOrDefault(
          c => c.CartId == ShoppingCartId
          && c.ProductId == id);


public class ShoppingCartActions : IDisposable
  {
    public string ShoppingCartId { get; set; }

    private ProductContext _db = new ProductContext();

    public const string CartSessionKey = "CartId";

    public void AddToCart(int id)
    {
      // Retrieve the product from the database.           
      ShoppingCartId = GetCartId();

      var cartItem = _db.ShoppingCartItems.SingleOrDefault(
          c => c.CartId == ShoppingCartId
          && c.ProductId == id);
      if (cartItem == null)
      {
        // Create a new cart item if no cart item exists.                 
        cartItem = new CartItem
        {
          ItemId = Guid.NewGuid().ToString(),
          ProductId = id,
          CartId = ShoppingCartId,
          Product = _db.Products.SingleOrDefault(
           p => p.ProductID == id),
          Quantity = 1,
          DateCreated = DateTime.Now
        };

        _db.ShoppingCartItems.Add(cartItem);
      }
      else
      {
        // If the item does exist in the cart,                  
        // then add one to the quantity.                 
        cartItem.Quantity++;
      }
      _db.SaveChanges();
    }

    public void Dispose()
    {
      if (_db != null)
      {
        _db.Dispose();
        _db = null;
      }
    }

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yguyon28Asked:
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it_saigeDeveloperCommented:
This line:

var cartItem = _db.ShoppingCartItems.SingleOrDefault(
          c => c.CartId == ShoppingCartId
          && c.ProductId == id);

Basically just means, based on the search criteria [CartID equals ShoppingCartID and ProductID equals id], I am expecting a single cart item.  Give me that single cart item.

If a single cart item cannot be found (or multiple cart items are found), then give me a default cart item (in this case a null object of the same type as cartItem).

The same goes for product.

-saige-
0
 
yguyon28Author Commented:
And also this line of code

 Product = _db.Products.SingleOrDefault(
           p => p.ProductID == id)

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