Error passing a DataTable object back from Powershell function [duplicate] - sql-server

Question

I've been trying to write a utility function that will return initialized [System.Data.DataTable] object data type.
I am aware of the annoying PowerShell functions return behavior where it tries to "unroll" everything into a [System.Array] return type.
Previously I have always managed to get around that problem.
Usually using the "comma trick" to return your own array #(,$result) aways worked - however this time this does not seem to make a difference and I've run out of options...
Another trick I normally use is the $null assignments within the Process block (see my code bellow) - this way I fool the pipeline there is nothing to "unroll" on the output...
I am not taking impossible for an answer, so far based on my experience nothing is impossible in PowerShell :)
Here is my code:
function Get-SourceDataTable
{
[OutputType([System.Data.DataTable])]
[cmdletbinding()]
param(
[parameter(Mandatory=$true, Position=0)]
[System.Data.SqlClient.SqlBulkCopy] $Destination,
[parameter(Mandatory=$true, Position=1)]
[System.Collections.Specialized.OrderedDictionary] $ColumnDefinition,
[parameter(Mandatory=$false, Position=2)]
[int]$ColumnStartIndex = 0
)
BEGIN{
$datatable = New-Object System.Data.DataTable
$colIndex = $ColumnStartIndex
}
PROCESS{
$ColumnDefinition.Keys |
foreach {
$null = $datatable.Columns.Add($_, $ColumnDefinition[$_]) # define each column name and data type
$null = $Destination.ColumnMappings.Add($_, $colIndex) # map column to destination table
$colIndex++
}
}
END{
return ,$datatable
}
}
I hope someone can get this code working...

Answer 1

Rather than return use Write-Output -NoEnumerate. For example:
function New-DataTable {
$datatable = New-Object System.Data.DataTable
$null = $datatable.Columns.Add("x",[int])
$null = $datatable.Columns.Add("y",[int])
$null = $datatable.Rows.Add(#(1,2))
$null = $dataTable.Rows.Add(#(3,4))
Write-Output -NoEnumerate $datatable
}
New-DataTable | Get-Member
Note however that if you just type New-DataTable, it might look like enumberated rows, but Get-Member tells you the actual type returned.

Answer 2

I got the function from the question to return DataTable type when I used LoadWithPartialName to load the assembly containing the type and pipe it out with Out-Null.
Don't ask my why, but feel free to comment if you know the reason.
The working function code is below. Note the return statement is not necessary I only use it to improve code readability:
function Get-SourceDataTable
{
[OutputType([System.Data.DataTable])]
[cmdletbinding()]
param(
[parameter(Mandatory=$true, Position=0)]
[System.Data.SqlClient.SqlBulkCopy] $Destination,
[parameter(Mandatory=$true, Position=1)]
[System.Collections.Specialized.OrderedDictionary] $ColumnDefinition,
[parameter(Mandatory=$false, Position=2)]
[int]$ColumnStartIndex = 0
)
BEGIN{
[System.Reflection.Assembly]::LoadWithPartialName("System.Data") | Out-Null
$datatable = New-Object System.Data.DataTable
$colIndex = $ColumnStartIndex
}
PROCESS{
$ColumnDefinition.Keys |
foreach {
$null = $datatable.Columns.Add($_, $ColumnDefinition[$_]) # define each column name and data type
$null = $Destination.ColumnMappings.Add($_, $colIndex) # map column to destination table
$colIndex++
}
}
END{
return ,$datatable
}
}
To summarize all known possible solutions to the problem of forcing PowerShell function to return specific data type:
use $null assignments
use comma to return an array ,$variable
use LoadWithPartialName("Assembly.Name") | Out-Null
use Write-Output -NoEnumerate $variable to return the type - credit goes to Burt_Harris
Finally, after the input from Burt_Harris (THANKS Burt!) the final working version of the function from this question is this:
function Get-SourceDataTable
{
[OutputType([System.Data.DataTable])]
[cmdletbinding()]
param(
[parameter(Mandatory=$true, Position=0)]
[System.Data.SqlClient.SqlBulkCopy] $Destination,
[parameter(Mandatory=$true, Position=1)]
[System.Collections.Specialized.OrderedDictionary] $ColumnDefinition,
[parameter(Mandatory=$false, Position=2)]
[int]$ColumnStartIndex = 0
)
BEGIN{
#[System.Reflection.Assembly]::LoadWithPartialName("System.Data") | Out-Null
$datatable = New-Object System.Data.DataTable
$colIndex = $ColumnStartIndex
}
PROCESS{
$ColumnDefinition.Keys |
foreach {
$null = $datatable.Columns.Add($_, $ColumnDefinition[$_]) # define each column name and data type
$null = $Destination.ColumnMappings.Add($_, $colIndex) # map column to destination table
$colIndex++
}
}
END{
#return ,$datatable
Write-Output -NoEnumerate $datatable
}
}