Linq到实体

Question

How to get rid of "If then else" ?

  If qShoppingCartByCartID.Invoke(_context).Count > 0 Then
            Return qShoppingCartByCartID.Invoke(_context).Select(Function(x) x.Products.UnitCost - x.Products.SalePrice).Sum
        Else
            Return 0
        End If

Answer 1

If the list is empty then Sum() will return null - so you could just return the sum:

  Return qShoppingCartByCartID.Invoke(_context).Select(Function(x) x.Products.UnitCost - x.Products.SalePrice).Sum()

In C# you could also use ?? to turn that into a zero instead of null if you wanted to

  return qShoppingCartByCartID....Sum() ?? 0;

I'm not a VB user, but it looks like you can do this same null coallescing in VB using If - see Is there a VB.NET equivalent for C#'s '??' operator?