public void AddItem(AddToBasketViewModel item)
{
var existingItem = _items.SingleOrDefault(model => model.Id == item.Id);
if (existingItem == null)
{
_items.Add(item);
return;
}
existingItem.Merge(item);
}
public void Merge(AddToBasketViewModel item)
{
if (item.Id != Id)
{
throw new InvalidOperationException();
}
if (item.Description != Description)
{
throw new InvalidOperationException();
}
Quantity += item.Quantity;
}