How to get Lambda in LINQ to actually filter for dynamic linq - vb.net

Question

Example-I have a person class
Public Class Person
Private _fname As String
Public Property Fname() As String
Get
Return _fname
End Get
Set(ByVal value As String)
_fname = value
End Set
End Property
Private _lname As String
Public Property Lname() As String
Get
Return _lname
End Get
Set(ByVal value As String)
_lname = value
End Set
End Property
Private _age As Integer
Public Property Age() As Integer
Get
Return _age
End Get
Set(ByVal value As Integer)
_age = value
End Set
End Property
End Class
Dim people As New List(Of Person)
people.Add(New Person With {.Fname = "Alice", .Lname = "Apples", .Age = 1})
people.Add(New Person With {.Fname = "Bob", .Lname = "Banana", .Age = 2})
people.Add(New Person With {.Fname = "Charlie", .Lname = "Cherry", .Age = 3})
people.Add(New Person With {.Fname = "Dave", .Lname = "Durian", .Age = 4})
people.Add(New Person With {.Fname = "Eric", .Lname = "EggPlant", .Age = 10})
Dim filteredPerson = From person In people
filteredPerson.Where(Function(fp) fp.Fname = "Bob")
Dim finalList = filteredPerson.ToList
For Each p In finalList
Debug.Print("FNAME: " + p.Fname)
Next
This still returns all 5 people, like the where is not being applied, what am I doing wrong?
I would also like to be able to pass a list of names and return only those
Dim searchList As New List(Of String)
searchList.Add("Bob")
searchList.Add("Dave")
Dim filteredPerson = From person In people
For Each s In searchList
Dim innerName As String = s
filteredPerson.Where(Function(fp) fp.Fname = innerName)
Next
Dim finalList = filteredPerson.ToList
For Each p In finalList
Debug.Print("FNAME: " + p.Fname)
Next

Answer 1

The problem is that Where doesn't change the collection. It returns the newly filtered collection.
Try this:
Dim filteredPerson = people.Where(Function(fp) fp.Fname = "Bob")
(By the way, I don't see anything dynamic in here... where are you using dynamic LINQ?)
To add multiple Where clauses, you'll want something like this:
Dim searchList As New List(Of String)
searchList.Add("Bob")
searchList.Add("Dave")
Dim filteredPerson As IEnumerable(Of String) = people
For Each s In searchList
Dim innerName As String = s
filteredPerson = filteredPerson.Where(Function(fp) fp.Fname = innerName)
Next
Dim finalList = filteredPerson.ToList
For Each p In finalList
Debug.Print("FNAME: " + p.Fname)
Next
However, I don't believe that's actually what you want to do. Each Where clause is going to insist that Fname is the specified name - and it's not going to be both Bob and Dave! I think you actually want something which can be expressed much more simply:
Dim searchList As New List(Of String)
searchList.Add("Bob")
searchList.Add("Dave")
Dim filteredPerson = people.Where(Function(fp) searchList.Contains(fp.Fname))
Dim finalList = filteredPerson.ToList
For Each p In finalList
Debug.Print("FNAME: " + p.Fname)
Next
All we want to know is whether Fname is in searchList, which is what Contains does.

Answer 2

Dim people As New List(Of Person)
people.Add(New Person With {.Fname = "Alice", .Lname = "Apples", .Age = 1})
people.Add(New Person With {.Fname = "Bob", .Lname = "Banana", .Age = 2})
people.Add(New Person With {.Fname = "Charlie", .Lname = "Cherry", .Age = 3})
people.Add(New Person With {.Fname = "Dave", .Lname = "Durian", .Age = 4})
people.Add(New Person With {.Fname = "Eric", .Lname = "EggPlant", .Age = 10})
Dim searchList As New List(Of String)
searchList.Add("Bob")
searchList.Add("Dave")
dim filteredItems = from p in people _
join i in searchList on p.FName equals i _
select p
dim personFound as Person
for each personFound in filteredItems
Console.WriteLine(personFound.Lname)
next