System.Data.DataTable Becomes Null When Returned from Function on ARM64 and AMD64 Platforms (Windows, macOS & Linux)

[cameronfairbairn]

Prerequisites

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Steps to reproduce

When a System.Data.DataTable object is instantiated within a PowerShell function and then returned to the calling scope, the returned value incorrectly becomes $null. This issue has been observed across multiple platforms (Windows AMD64, macOS ARM64, Linux ARM64) and affects multiple recent PowerShell versions, including LTS (7.4) and the latest stable (7.5) and preview (7.6).

Directly creating and manipulating a System.Data.DataTable object outside of a function scope works correctly. Returning other object types (e.g., System.Collections.Hashtable) from functions also works correctly. This suggests an issue specific to how System.Data.DataTable objects are handled or marshalled across function boundaries in recent PowerShell versions, likely introduced sometime after PowerShell 7.3.

Run the following PowerShell code on an affected platform/version (e.g., Windows 10/11 with PS 7.4+, macOS ARM64 with PS 7.4+, Linux ARM64 with PS 7.4+):

Write-Host "Testing DataTable return issue on $($PSVersionTable.PSVersion) / $($PSVersionTable.OS)"

function New-EmptyDataTable {
    Write-Host "[Inside Function] Attempting to create DataTable..."
    $dt = New-Object System.Data.DataTable
    if ($dt -eq $null) {
        Write-Error "[Inside Function] FAILED to create DataTable object!"
        return "FUNCTION_FAILED_CREATION" # Should not happen based on tests
    } else {
        # Object creation inside the function appears successful
        Write-Host "[Inside Function] DataTable created. Type: $($dt.GetType().FullName). Returning..."
        return $dt # Attempt to return the created DataTable
    }
}

Write-Host "[Main Scope] Calling function..."
$resultTable = $null # Ensure it's null before call
try {
    $resultTable = New-EmptyDataTable
} catch {
    Write-Error "[Main Scope] Error calling function: $_"
}

Write-Host "[Main Scope] Function call complete."
Write-Host "[Main Scope] Checking returned value..."

if ($resultTable -eq $null) {
    Write-Error "[Main Scope] TEST FAILED: Returned DataTable is NULL." # This error occurs
} elseif ($resultTable -is [string] -and $resultTable -eq "FUNCTION_FAILED_CREATION") {
    Write-Error "[Main Scope] TEST FAILED: Function indicated internal creation failure."
} elseif ($resultTable -is [System.Data.DataTable]) {
    Write-Host "[Main Scope] TEST SUCCEEDED: Returned value is a DataTable." # This is expected
    Write-Host "[Main Scope] Returned Type: $($resultTable.GetType().FullName)"
} else {
    Write-Warning "[Main Scope] UNEXPECTED RESULT: Returned value is not null, but also not a DataTable."
    Write-Warning "[Main Scope] Returned Type: $($resultTable.GetType().FullName)"
    Write-Warning "[Main Scope] Returned Value: $resultTable"
}

Write-Host "--- Test Complete ---"

Expected behavior

[Main Scope] TEST SUCCEEDED: Returned value is a DataTable.
[Main Scope] Returned Type: System.Data.DataTable

Actual behavior

Write-Error: [Main Scope] TEST FAILED: Returned DataTable is NULL.

Error details

The bug causes the function to return $null. The following error occurs when attempting to use the $null variable that was incorrectly returned (e.g., trying to access a property or method):

Exception             :
    Type    : Microsoft.PowerShell.Commands.WriteErrorException
    Message : [Main Scope] TEST FAILED: Returned DataTable is NULL.
    HResult : -2146233087
CategoryInfo          : NotSpecified: (:) [Write-Error], WriteErrorException
FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorException
InvocationInfo        :
    MyCommand       : if ($resultTable -eq $null) {
                      Write-Error "[Main Scope] TEST FAILED: Returned DataTable is NULL."
                      } elseif ($resultTable -is [string] -and $resultTable -eq "FUNCTION_FAILED_CREATION") {
                      Write-Error "[Main Scope] TEST FAILED: Function indicated internal creation failure."
                      } elseif ($resultTable -is [System.Data.DataTable]) {
                      Write-Host "[Main Scope] TEST SUCCEEDED: Returned value is a DataTable."
                      Write-Host "[Main Scope] Returned Type: $($resultTable.GetType().FullName)"
                      } else {
                      Write-Warning "[Main Scope] UNEXPECTED RESULT: Returned value is not null, but also not a DataTable."
                      Write-Warning "[Main Scope] Returned Type: $($resultTable.GetType().FullName)"
                      Write-Warning "[Main Scope] Returned Value: $resultTable"
                      }
    HistoryId       : 4
    CommandOrigin   : Internal
ScriptStackTrace      : at <ScriptBlock>, <No file>: line 2

Environment data

PowerShell 7.4.7 (from tag: lts-7.4-azurelinux-3.0-arm64)

    PowerShell 7.5.0 (from tag: 7.5-azurelinux-3.0-arm64)

    PowerShell 7.6.0-preview.3 (from tag: preview-7.6-azurelinux-3.0-arm64)

Visuals

No response

[iRon7]

Is there any PowerShell version that does work? As there are at least two PowerShell gotchas in play here: The datatable will be unrolled to an enumerable null with will be eventually a $Null when assigned.

To prevent this, use the comma operator (,):

return ,$dt

Or use Write-Output -NoEnumerate

See also: https://stackoverflow.com/q/55373450/1701026

Besides:

$Null should be at the left-hand side of the operator:

if ($null -eq $resultTable) { ...

See also: Checking for $Null

[rhubarb-geek-nz]

See Binders.cs line 613

DataTable is treated as an enumerable so both assignment and writing to pipelines are affected.

You have my sympathy, it is really difficult dealing with strict data structures when PowerShell deliberately evaporates a container and having to treat a list of one or zero items as special cases to be tested for.

function New-EmptyDataTable {
   New-Object System.Data.DataTable
}

Would work, no need for return statement or assignment. Use $ErrorActionPreference or -ErrorAction to trap errors.

I would be wary of using common C# coding patterns with PowerShell. My approach to SQL databases and PowerShell is to read a result set and write directly to a pipeline output for each row. So you can read from SQL at the start of the pipeline and process the records as they are streamed in parallel.

$Command = $Connection.CreateCommand()

$Command.CommandText = $CommandText

Read-DbCommand -Command $Command | Format-Table

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This issue has been marked as answered and has not had any activity for 1 day. It has been closed for housekeeping purposes.

[microsoft-github-policy-service]

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