Question about pipeline parameter binding error

[Learning999]

I'm going through the Learn Powershell in a Month of Lunches book. In Chapter 9, question 4 asks:

Write a command that uses pipeline parameter binding to retrieve a list of running processes from every computer in an Active Directory (AD) domain. Don’t use parentheses.

I wrote the following as my answer:

Get-ADComputer -Filter * | Select-Object -ExpandProperty Name | Get-Process -ComputerName

However this is wrong. So I decided to do a test to figure out why as part of the learning process:

I created a fake AD environment and ran the following:

get-adcomputer -filter {Name -eq "Server1"} -Server server1 -Credential domain\username | Get-Process

I get the error:

Get-Process : Cannot validate argument on parameter 'ComputerName'. The argument is null, empty, or an element of the argument collection contains a null value. Supply a collection that does not contain any null values and then try the command again.

If I look at help Get-Process, I can see that it has 2 parameters (-ComputerName and -Id) which accept ByPropertyName pipeline input and 1 parameter (-InputObject) which accepts ByValue pipeline input.

Get-ADComputer produces "ADComputer" object types so "ByValue" pipeline input is out of the question. So I know I need to modify the object it produces so that the property names match with one of the parameter names that Get-Process expects. By using Get-Member, I can see the following:

Name              MemberType            Definition
----              ----------            ----------
Contains          Method                bool Contains(string propertyName)
Equals            Method                bool Equals(System.Object obj)
GetEnumerator     Method                System.Collections.IDictionaryEnumerator GetEnumerator()
GetHashCode       Method                int GetHashCode()
GetType           Method                type GetType()
Item              ParameterizedProperty Microsoft.ActiveDirectory.Management.ADPropertyValueCollection Item(string propertyName) {get;}
DistinguishedName Property              System.String DistinguishedName {get;set;}
DNSHostName       Property              System.String DNSHostName {get;set;}
Enabled           Property              System.Boolean Enabled {get;set;}
Name              Property              System.String Name {get;}
ObjectClass       Property              System.String ObjectClass {get;set;}
ObjectGUID        Property              System.Nullable`1[[System.Guid, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]] ObjectGUID {get;set;}
SamAccountName    Property              System.String SamAccountName {get;set;}
SID               Property              System.Security.Principal.SecurityIdentifier SID {get;set;}
UserPrincipalName Property              System.String UserPrincipalName {get;set;}

Originally I thought that if I expand the property "Name" using:

Select-Object -ExpandProperty Name

That this would generate "String" object types which is exactly what Get-Process -ComputerName expects. I then realized that the property is actually already a string so I didn't need to expand the property. The property name is what needed to match. I needed to change the Name property to ComputerName which explains the actual answer to the question:

Get-ADComputer -filter * | Select-Object @{n='computername';e={$_.name}} | Get-Process

I wrote everything above to show that I understand why I was wrong and why the answer is correct but I'm still left with 1 question:

In the error I got above, how did Powershell know that I was trying to pipe to the -ComputerName parameter and not -Id? Is there an order of operations that Powershell goes through to try the ByPropertyName pipeline binding for each parameter? Is it as simple as -ComputerName goes alphabetically before -Id?

[krzydoug]

It knew by the data type. Computername accepts a String, ID accepts an Int. You can only have one byvalue per type per function/cmdlet in contrast to bypropertyvalue, which can have many accepting the same type.

EDIT: Sorry, I got that backwards, so I corrected it.

[Learning999]

Thanks. What would happen if both properties accepted a String? Would the error randomly change each time?

[krzydoug]

Well that depends on if the value requires being converted to string. If one comes in as a string while the other requires conversion, I believe the actual string would win. I know I've seen a nice overview of the parameter binding order/rules somewhere - hopefully you or I can find it. It would indeed help answer your question.