Convert string to PSCustomObject

Question

The problem I'm having stems from passing a PSCustomObject as an argument to the Start-Process cmdlet (I'm essentially starting a new PowerShell process to run a script asynchronously from the calling script). Although the parameter is defined as type PSCustomObject, it is accepted as a string for some reason, and therefore it looks like I am required to convert it back to a PSCustomObject to access any attributes.

Here is the necessary part of my calling script:

# Convert JSON object to PowerShell object
$payload = ConvertFrom-Json $body

Write-Host $payload
## Returns exactly the following PsCustomObject:

## @{os=Windows Server Datacenter 2016; vmName=sbtestvm; diskType=Managed; username=testuser;
## password=Pa55w.rd1234; location=West Europe; size=Standard_D1;
## requestType=0; sender=test}

Write-Host $payload.os
## Returns: Windows Server Datacenter 2016

# Fire up new worker shell asynchronously
Start-Process powershell.exe -ArgumentList '-NoExit', "$PSScriptRoot\ServiceBus-AsyncWorker.ps1", "'$payload'"  # -Windowstyle Hidden

And my executed script:

Param(
    [Parameter(Mandatory=$True)]
    [PSCustomObject]$Request
)

# Import RequestHandler module to deal with processing service bus requests
Import-Module $PSScriptRoot\RequestHandler\RequestHandler.psm1

Write-Host $Request
## Returns exactly the same as 'Write-Host $payload' in the calling script

Write-Host $Request.os
## Returns empty string

Write-Host $Request.GetType()
## Returns System.String <--- This is the issue

Long story short: is there a way to prevent this object being automatically parsed as a string in the first place? If not - how can this string be cast back to the relevant object type?

Answer 1

Start-Process powershell.exe starts a new PowerShell process. You cannot pass PowerShell objects across process boundaries.

You could change

Start-Process powershell.exe -ArgumentList '-NoExit', "$PSScriptRoot\ServiceBus-AsyncWorker.ps1", "'$payload'"

to

$PSScriptRoot\ServiceBus-AsyncWorker.ps1 $payload

to avoid creating a new process, but that will run the script in the same window.

If you need to run the script detached from the console you could run it as a background job:

$job = Start-Job -ScriptBlock {
    Param($Path, $Data)
    & "$Path\ServiceBus-AsyncWorker.ps1" $Data
} -ArgumentList $PSScriptRoot, $payload

Otherwise you need to pass the argument in serialized form (e.g. the original JSON) when spawning the new process:

Start-Process powershell.exe -ArgumentList '-NoExit', "$PSScriptRoot\ServiceBus-AsyncWorker.ps1", "`"$body`""

and then (re-)create the object from the string:

Param(
    [Parameter(Mandatory=$true)]
    [string]$Json
)

# Import RequestHandler module to deal with processing service bus requests
Import-Module $PSScriptRoot\RequestHandler\RequestHandler.psm1

$Request = ConvertFrom-Json $Json
...