Powershell returns different datatype depending on number of elements

Question

Currently I'm very confused with Powershell and how it handles Arrays/ArrayLists and PSObjects/CustomObjects.

High level:

I'm trying to Import a CSV file and inserting at specific lines "placeholder" entries. This is actually working fine. My only issue the moment is, in case the CSV contains only 1 Element (Line) Powershell Creates a PsCustomObject . If there are multiple lines, Powershell delivers an Array.

1 Element in `$pConnectionsOnMpDevice

$pConnectionsOnMpDevice  = ($pList | ?({$_.device -like "*$pDevice*"}))
($pConnectionsOnMpDevice).getType()

IsPublic IsSerial Name BaseType
True True PsCustomObject[] System.Object

n Element in $pConnectionsOnMpDevice

$pConnectionsOnMpDevice  = ($pList | ?({$_.device -like "*$pDevice*"}))
($pConnectionsOnMpDevice).getType()

IsPublic IsSerial Name BaseType
True True Object[] System.Array

Finally I try to add an Element:

$pConnectionsOnMpDevice += $MpObject

(One of my first approaches was to use (FYI):

#$pConnectionsOnMpDevice.Insert($index,$match)

If I try to add $MpObject to $pConnectionsOnMpDevice I get following error:

Method invocation failed because [System.Management.Automation.PSObject] does not contain a method named 'op_Addition'.
At C:\Scripts\PS_GenerateMPConfig\PS_GenerateMPConfig_06_f.ps1:90 char:13
+             $pConnectionsOnMpDevice += $MpObject
+             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (op_Addition:String) [], RuntimeException
    + FullyQualifiedErrorId : MethodNotFound

I assume it's the same issue as described here

I tried to cast $pConnectionsOnMpDevice to an Arraylist by:

[System.Collections.ArrayList]::$pConnectionsOnMpDevice  += $MpObject

But still no success.

Does anyone has an advice how I can add an element?

Answer 1

Use the array subexpression operator ( @() ) to force a value expression to return an array:

$pConnectionsOnMpDevice  = @($pList | ?({$_.device -like "*$pDevice*"}))

---

I tried to cast $pConnectionsOnMpDevice to an Arraylist by:

 [System.Collections.ArrayList]::$pConnectionsOnMpDevice += $MpObject 

That's not a cast, that's a static invocation - PowerShell will invoke whatever static method or property has the same name as "$pConnectionOnMpDevice" .

Remove the :: if you want a cast operation:

$array = 1,2,3
$arraylist = [System.Collections.ArrayList]$array