Powershell querying users in Active Directory - powershell

Question

I am having a hard time figuring out a more efficient way of querying info from AD. As it stands I import a .csv file of active users from our student information system. Then I want to create a new .csv file of active users info from AD. As such, I am querying AD on every user (approx 10k students.) I have a feeling I could somehow accomplish this with one query, but no luck. The students match on a numeric ID that is stored in the AD title field. The code does work, however it takes hours to run. Here is what I use:
$Users = Import-Csv "c:\DASLExport.csv" -Header #("a") | Select a
$usersarray = #()
ForEach ($Row in $Users) {
$userSearchString = $Row.a
$currentUser = (Get-ADUser -Filter {Title -eq $userSearchString} -Properties title, SamAccountName, extensionAttribute1)
$UserObj = New-Object PSObject
Add-Member -InputObject $UserObj -MemberType NoteProperty -Name "ID" -Value $($currentUser.title)
Add-Member -InputObject $UserObj -MemberType NoteProperty -Name "Username" -Value $($currentUser.SamAccountName)
Add-Member -InputObject $UserObj -MemberType NoteProperty -Name "Password" -Value $($currentUser.extensionAttribute1)
$usersarray += $UserObj
}
If($usersarray.count -gt 0) {$usersarray | Export-Csv -Path 'c:\users.csv' -NoTypeInformation}

Answer 1

I think, instead of query each user with Get-ADUser , Get all users with title at once and save it to a variable, Then query this variable instead.
Also, Regular Arrays are in fixed size, which mean that each time you insert new element you actually create new array and copy all the data into it, and you repeat it again and again, which take much time. so switch to ArrayList which is intend to grow, it will be much faster.
Check it yourself:
$ArrayList = New-Object System.Collections.ArrayList
$RegularArray = #()
Measure-Command { 1..10000 | % {[void]$ArrayList.Add($_)} }
Measure-Command { 1..10000 | % {$RegularArray += $_ } }
So For example try this:
$Users = Import-Csv "c:\DASLExport.csv" -Header #("a") | Select a
$ADUsers = Get-ADUser -Filter {Title -ne "$null"} -Properties title, SamAccountName, extensionAttribute1
$Usersarray = New-Object System.Collections.ArrayList
ForEach ($Row in $Users) {
$userSearchString = $Row.a
$currentUser = $ADUsers | ? {$_.Title -eq $userSearchString}
if (!$currentUser) {continue}
$UserObj = New-Object PSObject
Add-Member -InputObject $UserObj -MemberType NoteProperty -Name "ID" -Value $($currentUser.title)
Add-Member -InputObject $UserObj -MemberType NoteProperty -Name "Username" -Value $($currentUser.SamAccountName)
Add-Member -InputObject $UserObj -MemberType NoteProperty -Name "Password" -Value $($currentUser.extensionAttribute1)
[void]$usersarray.Add($UserObj)
}
If($usersarray.count -gt 0) {$usersarray | Export-Csv -Path 'c:\users.csv' -NoTypeInformation}

Answer 2

While #Avshalom's answer is useful, it can be improved:
[CmdletBinding()]
param
(
[Parameter(Position = 0)]
[ValidateScript({Test-Path -Path $PSItem -PathType Leaf})]
[string]
$Path = 'C:\DASLExport.csv',
[Parameter(Position = 1)]
[ValidateScript({Test-Path -Path $PSItem -PathType Leaf -IsValid})]
[string]
$Destination = 'C:\users.csv'
)
$csv = Import-Csv -Path $Path -Header a
$users = #(Get-ADUser -Filter 'Title -ne "$null"' -Properties Title, SamAccountName, extensionAttribute1)
$collection = foreach ($row in $csv)
{
$title = $row.a
$user = $users.Where{$PSItem.Title -eq $title}
if (-not $user)
{
Write-Warning -Message "User $title not found."
continue
}
[pscustomobject]#{
ID = $user.Title
Username = $user.SamAccountName
Password = $user.extensionAttribute1
}
}
$collection | Export-Csv -Path $Destination -NoTypeInformation
You can assign the output of the foreach loop to a variable directly, avoiding the need to manage a list object (although if you do opt for a list, you should use System.Collections.Generic.List<Type> since ArrayList is deprecated). Additionally, you don't need to use a Select-Object statement since your csv was already loaded and it just processes it twice in that scenario. The biggest speed improvement is not querying AD thousands of times, keeping it in a single object, but MOSTLY by not using [array]/#().
Speed comparisons:
$L = 1..100000
Measure-Command {$col = foreach ($i in $L) { $i }}
~70ms
Measure-Command {$col = [System.Collections.Generic.List[int]]::new(); foreach ($i in $L) { $col.Add($i) }}
~110ms
Measure-Command {$col = #(); foreach ($i in $L) { $col += $i }}
~46 SECONDS