Populate parameter list from XML

Question

I need to pull a list of IDs into a powershell paramater validateset like so:

function Do-Stuff {
   [Cmdletbinding()] 
   param(
        [ValidateSet("Seattle","NewYork","London","Atlanta" )]
        [String]$Site
    )

Instead of manually specifying the cities in the set, I'd like to pull from an existing xml document that already lists them all. Once loaded, the site names appear in $xml.var.sites.id. Is this possible, and probably more importantly, is it a good idea?

Answer 1

If your city names only contain alphanumeric characters, it might be a cleaner solution to create a custom enum type from the names, and specify your parameter value as that type:

Add-Type -TypeDefinition @"
   // very simple enum type
   public enum ValidSites
   {
      Seattle,
      NewYork,
      London,
      Atlanta
   }
"@

function Do-Stuff {
   [Cmdletbinding()] 
   param( [ValidSites]$Site )
}

It should have the same effect as using ValidateSet (including enabling tab completion of the possible values), without having to modify a list set in the function itself.

Answer 2

Had to to this for a recent project. Didn't realize how easy this was with an enum, thanks mjolinor!

An alternative is to use Dynamic Parameters. Find help using Get-Help:

#Look for the Dynamic Parameters section in here
Get-Help about_Functions_Advanced_Parameters

Other resources:

• about_Functions_Advanced_Parameters Online help
• This code from jrich523
• New-DynamicParam, mostly borrowed from jrich523

Current function definition:

Function New-DynamicParam {
<#
    .SYNOPSIS
        Helper function to simplify creating dynamic parameters

    .DESCRIPTION
        Helper function to simplify creating dynamic parameters

        Example use cases:
            Include parameters only if your environment dictates it
            Include parameters depending on the value of a user-specified parameter
            Provide tab completion and intellisense for parameters, depending on the environment

        Please keep in mind that all dynamic parameters you create will not have corresponding variables created.
           One of the examples illustrates a generic method for populating appropriate variables from dynamic parameters
           Alternatively, manually reference $PSBoundParameters for the dynamic parameter value

    .NOTES
        Credit to http://jrich523.wordpress.com/2013/05/30/powershell-simple-way-to-add-dynamic-parameters-to-advanced-function/
            Added logic to make option set optional
            Added logic to add RuntimeDefinedParameter to existing DPDictionary
            Added a little comment based help

    .PARAMETER Name
        Name of the dynamic parameter

    .PARAMETER ValidateSet
        If specified, set the ValidateSet attribute of this dynamic parameter

    .PARAMETER Mandatory
        If specified, set the Mandatory attribute for this dynamic parameter

    .PARAMETER ParameterSetName
        If specified, set the ParameterSet attribute for this dynamic parameter

    .PARAMETER Position
        If specified, set the Position attribute for this dynamic parameter

    .PARAMETER ValueFromPipelineByPropertyName
        If specified, set the ValueFromPipelineByPropertyName attribute for this dynamic parameter

    .PARAMETER HelpMessage
        If specified, set the HelpMessage for this dynamic parameter

    .PARAMETER DPDictionary
        If specified, add resulting RuntimeDefinedParameter to an existing RuntimeDefinedParameterDictionary (appropriate for multiple dynamic parameters)
        If not specified, create and return a RuntimeDefinedParameterDictionary (appropriate for a single dynamic parameter)

    .EXAMPLE

        function Show-Free
        {
            [CmdletBinding()]
            Param()
            DynamicParam {
                $options = @( gwmi win32_volume | %{$_.driveletter} | sort )
                New-DynamicParam -Name Drive -ValidateSet $options -Position 0 -Mandatory
            }
            begin{
                #have to manually populate
                $drive = $PSBoundParameters.drive
            }
            process{
                $vol = gwmi win32_volume -Filter "driveletter='$drive'"
                "{0:N2}% free on {1}" -f ($vol.Capacity / $vol.FreeSpace),$drive
            }
        } #Show-Free

        Show-Free -Drive <tab>

    # This example illustrates the use of New-DynamicParam to create a single dynamic parameter
    # The Drive parameter ValidateSet populates with all available volumes on the computer for handy tab completion / intellisense

    .EXAMPLE

    # I found many cases where I needed to add many dynamic parameters
    # The DPDictionary parameter lets you specify an existing dictionary
    # The block of code in the Begin block loops through bound parameters and defines variables if they don't exist

        Function Test-DynPar{
            [cmdletbinding()]
            param(
                [string[]]$x = $Null
            )
            DynamicParam
            {
                #Create the RuntimeDefinedParameterDictionary
                $Dictionary = New-Object System.Management.Automation.RuntimeDefinedParameterDictionary

                New-DynamicParam -Name AlwaysParam -options @( gwmi win32_volume | %{$_.driveletter} | sort ) -DPDictionary $Dictionary

                #Add dynamic parameters to $dictionary
                if($x -eq 1)
                {
                    New-DynamicParam -Name X1Param1 -Options 1,2 -mandatory -DPDictionary $Dictionary
                    New-DynamicParam -Name X1Param2 -DPDictionary $Dictionary
                    New-DynamicParam -Name X3Param3 -DPDictionary $Dictionary
                }
                else
                {
                    New-DynamicParam -Name OtherParam1 -mandatory -DPDictionary $Dictionary
                    New-DynamicParam -Name OtherParam2 -DPDictionary $Dictionary
                    New-DynamicParam -Name OtherParam3 -DPDictionary $Dictionary
                }

                #return RuntimeDefinedParameterDictionary
                $Dictionary
            }
            Begin
            {
                #This standard block of code loops through bound parameters...
                #If no corresponding variable exists, one is created
                    foreach($param in $PSBoundParameters.Keys)
                    {
                        if (-not ( Get-Variable -name $param -scope 0 -ErrorAction SilentlyContinue ) )
                        {
                            New-Variable -Name $Param -Value $PSBoundParameters.$param
                            Write-Verbose "Adding variable for dynamic parameter '$param' with value '$($PSBoundParameters.$param)'"
                        }
                    }

                #Appropriate variables should now be defined and accessible
                    Get-Variable -scope 0
            }
        }

    # This example illustrates the creation of many dynamic parameters using New-DynamicParam
        # You must create a RuntimeDefinedParameterDictionary object ($dictionary here)
        # To each New-DynamicParam call, add the -DPDictionary parameter pointing to this RuntimeDefinedParameterDictionary
        # At the end of the DynamicParam block, return the RuntimeDefinedParameterDictionary
        # Initialize all bound parameters using the provided block or similar code
#>
param(

    [string]
    $Name,

    [string[]]
    $ValidateSet,

    [switch]
    $Mandatory,

    [string]
    $ParameterSetName="__AllParameterSets",

    [int]
    $Position,

    [switch]
    $ValueFromPipelineByPropertyName,

    [string]
    $HelpMessage,

    [validatescript({
        if(-not ( $_ -is [System.Management.Automation.RuntimeDefinedParameterDictionary] -or -not $_) )
        {
            Throw "DPDictionary must be a System.Management.Automation.RuntimeDefinedParameterDictionary object, or not exist"
        }
        $True
    })]
    $DPDictionary = $false

)
    #Create attribute object, add attributes, add to collection   
        $ParamAttr = New-Object System.Management.Automation.ParameterAttribute
        $ParamAttr.ParameterSetName = $ParameterSetName
        if($mandatory)
        {
            $ParamAttr.Mandatory = $True
        }
        if($Position -ne $null)
        {
            $ParamAttr.Position=$Position
        }
        if($ValueFromPipelineByPropertyName)
        {
            $ParamAttr.ValueFromPipelineByPropertyName = $True
        }
        if($HelpMessage)
        {
            $ParamAttr.HelpMessage = $HelpMessage
        }

        $AttributeCollection = New-Object 'Collections.ObjectModel.Collection[System.Attribute]'
        $AttributeCollection.Add($ParamAttr)

    #param validation set if specified
        if($ValidateSet)
        {
            $ParamOptions = New-Object System.Management.Automation.ValidateSetAttribute -ArgumentList $ValidateSet
            $AttributeCollection.Add($ParamOptions)
        }


    #Create the dynamic parameter
        $Parameter = New-Object -TypeName System.Management.Automation.RuntimeDefinedParameter -ArgumentList @($Name, [string], $AttributeCollection)

    #Add the dynamic parameter to an existing dynamic parameter dictionary, or create the dictionary and add it
        if($DPDictionary)
        {
            $DPDictionary.Add($Name, $Parameter)
        }
        else
        {
            $Dictionary = New-Object System.Management.Automation.RuntimeDefinedParameterDictionary
            $Dictionary.Add($Name, $Parameter)
            $Dictionary
        }
}

An example using this function:

#Function has already been added to this session...
function Do-Stuff {
    [cmdletbinding()] 
    param()
    DynamicParam
    {
        #Example borrowing from TheMadTechnician: 
        #New-DynamicParam -Name Site -ValidateSet $(([xml](gc c:\temp\config.xml)).getElementsByTagName("City").Name) -Mandatory

        #I don't have that file... simplification
        New-DynamicParam -Name Site -ValidateSet "Seattle", "NewYork", "London", "Atlanta" -Mandatory
    }
    Begin
    {
        #This standard block of code loops through bound parameters...
        #If no corresponding variable exists, one is created
            foreach($param in $PSBoundParameters.Keys)
            {
                if (-not ( Get-Variable -name $param -scope 0 -ErrorAction SilentlyContinue ) )
                {
                    New-Variable -Name $param -Value $PSBoundParameters.$param
                    Write-Verbose "Adding variable for dynamic parameter '$param' with value '$($PSBoundParameters.$param)'"
                }
            }
        $Site
    }    
}

And finally, the end result:

One more example that has a few other dynamic parameters

Function New-LabMachine
{
    [cmdletbinding()]
    param(
        [ValidateSet("ADDSNew","ADDSExisting")]
        [string[]]
        $Role
    )
    DynamicParam
    {
        #Define dynamicparam dictionary.  Create a hashtable for splatting params
            $Dictionary = New-Object System.Management.Automation.RuntimeDefinedParameterDictionary
            $dict = @{DPDictionary = $Dictionary}

        #Add dynamic parameters to populate and validate Lab names
            $Labs = "Lab1", "Lab2" #@( Get-Lab | Select -ExpandProperty LabName -ErrorAction SilentlyContinue )
            New-DynamicParam -Name LabName -Mandatory -ValidateSet $Labs @dict

        if($Role -contains 'ADDSNew')
        {            
            #AD Forest info
                New-DynamicParam -Name DomainName -Mandatory @dict -HelpMessage "Provide domain name for first domain in forest"
                New-DynamicParam -Name ForestMode -Mandatory -ValidateSet "Win2008","Win2008R2","Win2012","Win2012R2" @dict
        }
        if($Role -contains 'ADDSExisting')
        {
            New-DynamicParam -Name DomainName -Mandatory @dict
            New-DynamicParam -Name username -Mandatory @dict
            New-DynamicParam -Name password -Mandatory @dict
        }

        #Return the dictionary for dynamic params
        $Dictionary
    }
    Begin
    {
        #This standard block of code loops through bound parameters...
        #If no corresponding variable exists, one is created
            foreach($param in $PSBoundParameters.Keys )
            {
                if (-not ( Get-Variable -name $param -scope 0 -ErrorAction SilentlyContinue ) -and "Verbose", "Debug" -notcontains $param )
                {
                    New-Variable -Name $Param -Value $PSBoundParameters.$param -Description DynParam
                    Write-Verbose "Adding variable for dynamic parameter '$param' with value '$($PSBoundParameters.$param)'"
                }
            }

        #Display the bound parameters      
        $PSBoundParameters.keys | ForEach-Object {Get-Variable -Name $_}
    }
}

And the results:

From my perspective, these can be very helpful to the end user. I typically use them to provide IntelliSense and tab completion support similar to what you are aiming for. As long as they provide you more value than their slight overhead and a little extra complexity, they are worth it : )

My apologies for the wall of text! Cheers!

Answer 3

Alternatively, if you want to use an file to validate against you can use ValidateScript instead of ValidateSet like such:

function Do-Stuff {
   [Cmdletbinding()] 
   param(
        [ValidateScript({if(([xml](gc c:\temp\config.xml)).getElementsByTagName("City").Name -contains $_){$true}else{throw ([xml](gc c:\temp\config.xml)).getElementsByTagName("City").Name}} )]
        [String]$Site
    )

That's based on the ridiculously simplistic XML file:

<?xml version="1.0"?>
<City_Validation_List>
    <City Name="Seattle"></City>
    <City Name="Atlanta"></City>
</City_Validation_List>

So, anyway, you can use ValidateScript to run a scriptblock as validation, in which you could load things from an XML file. ValidateSet on the other hand has to have a pre-defined array of strings to validate against.