I have a workflow that is pretty picky with the PSCustomObjects it receives. I often use Select-Object to get the properties from the objects I want to keep and sometimes I need to convert some of the values to more usable formats. The easiest way to do this is to use the @{Name='Name'; Expression = {'Expression'}} technique.

BUT, that technique messes up the PSCustomObject in a way that blocks my further workflow.

The issue can be reproduced like this:

$object = [pscustomobject]@{
        Text        = "This is a string"
    }

In the output below, the Definition for string is ‘string Text=This is a string’

$object | Select-Object * | Get-Member
<# Outputs
TypeName: System.Management.Automation.PSCustomObject

Name        MemberType   Definition
----        ----------   ----------
Equals      Method       bool Equals(System.Object obj)
GetHashCode Method       int GetHashCode()
GetType     Method       type GetType()
ToString    Method       string ToString()
Text        NoteProperty string Text=This is a string
#>

When adding a new NoteProperty with the Select-Object technique, the Definition is ‘System.String Text2=This is a string’

This is what makes my next cmdlet throw.

$WhatHappensToText = $object | Select-Object @{Name='Text'; Expression={$_.Text}} 
$WhatHappensToText | Get-Member
<# Outputs
TypeName: Selected.System.Management.Automation.PSCustomObject

Name        MemberType   Definition
----        ----------   ----------
Equals      Method       bool Equals(System.Object obj)
GetHashCode Method       int GetHashCode()
GetType     Method       type GetType()
ToString    Method       string ToString()
Text        NoteProperty System.String Text=This is a string
#>

When stripping the surplus like below, Definition is back to ‘string Text2=This is a string’

Exporting to Clixml and re-importing does the same

$WhatHappensToText | ConvertTo-Json | ConvertFrom-Json | Get-Member
<# Outputs
TypeName: System.Management.Automation.PSCustomObject

Name        MemberType   Definition
----        ----------   ----------
Equals      Method       bool Equals(System.Object obj)
GetHashCode Method       int GetHashCode()
GetType     Method       type GetType()
ToString    Method       string ToString()
Text        NoteProperty string Text=This is a string
#>

If I add the new NoteProperty like this, Definition is ‘string Text2=This is a string’ as I like it

$object2 = $object | Select-Object *
$object2 | foreach-object {$_ | Add-Member -MemberType NoteProperty -Name Text2 -Value $_.Text}
$object2 | Get-Member
<# Outputs
TypeName: Selected.System.Management.Automation.PSCustomObject

Name        MemberType   Definition
----        ----------   ----------
Equals      Method       bool Equals(System.Object obj)
GetHashCode Method       int GetHashCode()
GetType     Method       type GetType()
ToString    Method       string ToString()
Text        NoteProperty string Text=This is a string
Text2       NoteProperty string Text2=This is a string
#>

I have the following questions:

Why is the @{Name='Name'; Expression = {'Expression'}} technique adding System.String to the Definition and not string like in the Add-Member scenario?

Is there a way to make the @{Name='Name'; Expression = {'Expression'}} technique add a string and not a System.String?