I think this was the first time I ever used the [Select extension method][1]. And it gave me an unexpected result.
First I created a Person Class.
Public Class Person
Private _name As String
Public Sub New()
_name = "person1"
End Sub
Public Sub New(ByVal Name As String)
_name = Name
End Sub
Public Property Name() As String
Get
Return _name
End Get
Set(ByVal value As String)
_name = value
End Set
End Property
End Class
And what I wanted was to get a count of all the persons whose name was Test1.
So I created myself a testclass.
Imports NUnit.Framework
<testfixture()> _
Public Class TestIlistSelect
Private _persons As List(Of Person)
<SetUp()> _
Public Sub Setup()
_persons = New List(Of Person)
_persons.Add(New Person("Test1"))
_persons.Add(New Person("Test2"))
_persons.Add(New Person("Test3"))
End Sub
End Class```
And the first test I did was this.
```vbnet
<Test()> _
Public Sub If_Select_Name_As_Test1_Gives_1_Element()
Assert.AreEqual(1, _persons.Select(Function(x) x.Name = "Test1").Count)
End Sub```
Result
> <span class="MT_red">NUnit.Framework.AssertionException: Expected: 1<br /> But was: 3</span>
Not good.
Ok, next attempt.
```vbnet
<Test()> _
Public Sub If_Select_Name_As_Test1_Gives_1_Element_2()
Assert.AreEqual(1, (_persons.Select(Function(x) x.Name = "Test1")).Count)
End Sub```
Same result.
Next up.
```vbnet
<Test()> _
Public Sub If_Select_Name_As_Test1_Gives_1_Element_3()
Dim results = _persons.Select(Function(x) x.Name = "Test1")
Assert.AreEqual(1, results.Count)
End Sub```
And again nothing.
Time to look at what it is doing by debugging it.
I thought Select was returning an array of Persons. But it isn’t it is returning an array of booleans. Where it gives you the result of the statement.
So I actually got the following as a result.
> True
> False
> False
Now on to the next test, just to see if I am right.
```vbnet
<Test()> _
Public Sub If_Select_Name_As_Test1_Gives_1_Element_4()
Dim results = _persons.Select(Function(x) x.Name = "Test1")
Dim i = 0
For Each result In results
If result = True Then
i += 1
End If
Next
Assert.AreEqual(1, i)
End Sub```
And yes this gives me <span class="MT_green">Success</span>.
Woohoo.
But while digging through the different extension methods I also found this one.
```vbnet
<Test()> _
Public Sub If_Count_Name_As_Test1_Gives_1_Element_3()
Assert.AreEqual(1, _persons.LongCount(Function(x) x.Name = "Test1"))
End Sub```
Which gives me the result I want in a shorter fashion and more readable way.
> <span class="MT_red">All the above because I misunderstood what the Select was supposed to give me. Alex told me to use the Where method instead which gives me the result I wanted. I do not think that the Select method is very intuitive.</span>
[1]: http://msdn.microsoft.com/en-us/library/bb548891.aspx
Chris is awesome.