Question

I’ve a class that has a list of IDs with a function for adding new IDs from a list of objects.

I’ve got this resolved, but I’m sure this can be done with much less code.

Public Class Page    Private _IdList As List(Of Integer)   Private _HasNewItems As Boolean = False    Public Sub AddItems(ByVal Items As List(Of Item))      Dim itemsID = From itemX In Items _                   Select itemX.ID      Dim list As List(Of Integer) = itemsID.ToList      If _IdList.Intersect(list).Count = list.Count Then       _HasNewItems = False     Else       _HasNewItems = True       _IdList.AddRange(list)       _IdList = _IdList.Distinct     End If    End Sub  End Class 

So how can this be done with less code and more from a NET 3.5 perspective…

Answer 1

Try the following

Public Sub AddItems(ByVal items as List(Of Item))   Dim oldCount = _IdList.Count   _IdList.AddRange(items.Select(Function(x) x.ID).Except(_IdList))   _HasNewItems = oldCount < _IdList.Count End Sub 

The trick here is that Except will return all items Except when they are present in the enumerable passed as the argument (In this case _IdList). So items.Except(_IdList) is all new items.