ShoppingCartEntity.cs

[JsonObject(MemberSerialization.OptIn)]
public class ShoppingCartEntity : IShoppingCart
{
 
    [JsonProperty("list")]
    private List<CartItem> list { get; set; } = new List<CartItem>();
 
    public void Add(CartItem item)
    {
        // Get existing
        var existingItem = this.list.FirstOrDefault(i => i.ProductId == item.ProductId);
 
        if (existingItem == null)
        {
            this.list.Add(item);
        }
        else
        {
            existingItem.Count += item.Count;
        }
    }
 
    public void Remove(CartItem item)
    {
        var existingItem = this.list.FirstOrDefault(i => i.ProductId == item.ProductId);
 
        if (existingItem == null)
        {
            return;
        }
 
        if (existingItem.Count > item.Count)
        {
            existingItem.Count -= item.Count;
        }
        else
        {
            this.list.Remove(existingItem);
        }
    }
 
    public Task<ReadOnlyCollection<CartItem>> GetCartItems()
    {
        return Task.FromResult(this.list.AsReadOnly());
    }
 
     [FunctionName(nameof(ShoppingCartEntity))]
     public static Task Run([EntityTrigger] IDurableEntityContext ctx)
            => ctx.DispatchAsync<ShoppingCartEntity>();
}