PowerShell function ValueFromPipelineByPropertyName not using alias parameter name

Question

Trying to create a function that takes objects on the pipeline using the alias property. I\'m not sure where this is going wrong.

Example of the process:

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Answer 1

The AD Cmdlets are to blame here

The problem here is that the AD Cmdlets return objects in really non-standard ways. For instance, with any other cmdlet if you take the output of the command and select a non-existing property, you'll get back nothing, like this:

get-date | select Hamster

Hamster                                                                                                                                                                                                                        
-------     

>

See, nothing. Sure, it says Hamster, but there is no actual Object there. This is standard PowerShell behavior.

Now, look at what Get-ADUser does instead:

get-aduser -Filter {sn -eq 'adkison'} | select Hamster

Hamster                                                                                                                                                                                                                        
-------                                                                                                                                                                                                                        
{}                    

It creates a $null! So what will happen with your function is that PowerShell will look for a property of -LastName or -FirstName, get a $null and then stop right there. It sucks!

The best way around this is to swap the parameter names like this, and it will still work:

function Get-Name
{
  Param
  (
    [Parameter(ValueFromPipelineByPropertyName=$true)]
    [alias('FirstName')]
    [System.String] $givenname,

    [Parameter(ValueFromPipelineByPropertyName=$true)]
    [alias("sn","lastname")]
    [System.String] $Surname
  )
  write-host "firstName = $givenname / $($givenname.GetType().FullName)"
  Write-host "LastName  = $SurName  / $($SurName.GetType().FullName)"
}


get-aduser -Filter {sn -eq 'adkison'} | Get-Name

firstName = James / System.String
LastName  = Adkison  / System.String

Want to know more?

Check out this awesome answer from /u/JBSmith on the topic.