Hierarchy class Linq search

Question

I am trying to use Linq to search for a certain Product. How would I conduct this?

public class ShoppingCart : List<CartLine>
{
    // implement constructors you want available
    public ShoppingCart(){}

    public ShoppingCart( IEnumerable<CartLine> collection ) : base( collection ) {}

    public ShoppingCart( int capacity ) : base( capacity ) {}
}

public class CartLine
{
    public int CartLineId { get; set; }
    public Product Product { get; set; }
    public int Quantity { get; set; }
}

public class Product
{
    public int ProductId { get; set; }
    public string ProductName { get; set; }
    public string ProductDescription { get; set; }
    public string ImageLocation { get; set; }

    public int? ProductCategoryId { get; set; }
    public virtual ProductCategory ProductCategory { get; set; }
}

ShoppingCart shoppingCart = new ShoppingCart();

Linq Query Search: This keeps giving me errors, trying to use Resharper to get this in my repository pattern, testing

 shoppingCart.Find(p=>p.CartLine.Product.ProductName) = "SamsungTV"

Hi! In first, the predicate that is used in linq expression is wrong: it must return a boolean result. I think you want to use `shoppingCart.Find(p=>p.CartLine.Product == "SamsungTV")`. But `Product` property of a `CartLine` instance is not string. See [documentation](https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.list-1.find?view=netframework-4.7.2) to use the method properly. — Alexander, Oct 14 '18 at 06:41
What are you trying to do? search for `Product` with name `"SamsungTV"`? — Guy, Oct 14 '18 at 06:41
you got it I believe, shoppingCart.Find(p => p.Product.ProductName == "SamsungTV"); Thanks — TVLamp, Oct 14 '18 at 06:45
This is not linq. The `Find` method belongs to the `List` class. Also, you should read [Eric Lippert's answer](https://stackoverflow.com/a/21694054/3094533) to Why not inherit from List? And another thing - you can simply use a `Dictionary` to store the cart, where the `int` stands for quantity, and remove the `CartLine` class. — Zohar Peled, Oct 14 '18 at 06:47
so many good suggestions, I was reading from here, he has Cartlineid, but thanks for the input https://github.com/Apress/pro-asp.net-core-mvc-2/blob/master/10%20-%20SportsStore%20-%20Cart/SportsStore/SportsStore/Models/Cart.cs — TVLamp, Oct 14 '18 at 06:51

score 2 · Accepted Answer · answered Oct 14 '18 at 06:45

2

In the line shoppingCart.Find(p=>p.CartLine.Product.ProductName), p is already a CartLine. You also need to compare ProductName inside the query. Try

CartLine cartLine = shoppingCart.Find(p => p.Product.ProductName == "SamsungTV");

answered Oct 14 '18 at 06:45

Guy

46,488
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score 1 · Answer 2 · answered Oct 14 '18 at 07:16

1

For LINQ can u use a "where" :

var result =  shoppingCart.Product.Where(x => x.ProductName == "SamsungTV").ToList();

now you will have as a list of all in "Result" only where product name is Samsung TV ,to do what you like with it.

answered Oct 14 '18 at 07:16

Samuel Leiton

70
9

Alexander · Answer 3 · 2018-10-14T07:05:49.133

If you want to find instance of CartLine that' product name is "SamsungTV" you could use the following expression:

CartLine cartLine = shoppingCart.Find(p => String.Equals(p.Product?.ProductName, "SamsungTV", StringComparison.OrdinalIgnoreCase));

It will find product using ordinal (binary) sort rules and ignoring the case of product name. If you want to use another string comparison rules, define it using StringComparison enumeration.

Hierarchy class Linq search

3 Answers3