How to return nested List in Entity Framework

Question

I have two classes ShoppingCart and CartItems like this:

public class ShoppingCart
{
    public Guid Id { get; set; }
    public DateTime CreatedOn { get; set; }
    public Guid OwnerId { get; set; }
    public ICollection<CartItem> Items { get; set; }
}

 public class CartItem
 {
        public Guid Id { get; set; }}
        public int Quantity { get; set; }
        public Guid ProductId { get; set; }
        public Guid ShoppingCartId { get; set; }
}

I want get all CartItems by ownerId using this method:

public IEnumerable<CartItem> GetCartItems(Guid ownerId)
{
    return _shoppingCarts.Where(row => row.OwnerId == ownerId)
                         .Select(row => row.Items)
                         .ToList() ; 
}

but it returns an error :

Cannot implicitly convert type System.Collections.Generic.List<System.Collections.Generic.ICollection<CartItem>>'to System.Collections.Generic.IEnumerable<CartItem>

Domysee · Accepted Answer · 2016-03-30 08:51:08Z

5

The current return value of your method is of type IEnumerable<List<CartItem>>.

Instead of Select you should use SelectMany, like this:

public IEnumerable<CartItem> GetCartItems(Guid ownerId)
{
    return _shoppingCarts.Where(row => row.OwnerId == ownerId).SelectMany(row => row.Items).ToList() ; 
}

SelectMany flattens the collection of collections of CartItem to one collection of CartItem.

edited Mar 30, 2016 at 8:51

answered Mar 30, 2016 at 8:47

Domysee

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Pedro G. Dias · Accepted Answer · 2016-03-30 08:44:26Z

0

public class ShoppingCart
{
    public Guid Id { get; set; }
    public DateTime CreatedOn { get; set; }
    public Guid OwnerId { get; set; }
    public virtual ICollection<CartItem> Items { get; set; }
}

You forgot to add virtual to your ICollection of CartItems. Now when you load a shoppingCart, you can do:

var shoppingCart = _shoppingCarts.Include("CartItems").Where(cart => cart.Id == id);

So, to filter for ownerId, you can rewrite your query correspondingly. Just remember to include the items.

answered Mar 30, 2016 at 8:44

Pedro G. Dias

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2 Comments

temp125050 Over a year ago

I dont need shoppingCart Entity , I want get collection Of CartItem without ShoppingCart

Pedro G. Dias Over a year ago

Even easier. Just make sure your CartItems are part of your Context class, so you can query on them directly

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