why can't I add a member to an ADobject - powershell

Question

If I have an object of type Microsoft.ActiveDirectory.Management.ADObject, I can't use Add-Member to add a note property, unless I use -force. If I don't use the force directive, I get an error like:
Add-Member : Cannot add a member with the name "SAMAccountName"
because a member with that name already exists. To overwrite the
member anyway, add the Force parameter to your command.
But, it doesn't already exist. And that happens for any property name. For example:
$domainAccount | Add-Member -NotePropertyName SAMAccountName -NotePropertyValue $account.name
But, this works:
$domainAccount | Add-Member -NotePropertyName SAMAccountName -NotePropertyValue $account.name -force
I can't find documentation that explains this. Can you explain it? And, is there any danger in doing this with the -force directive?

Answer 1

The ADObject class behaves a bit clumsy, in that by simply asking if a property exists, you cause the property to be created if it doesn't.
When Add-Member checks for whether the SAMAccountName property already exists, it incidentally cause it to be created.
Just use the -Force parameter switch.
You can reproduce this behavior yourself:
Import-Module ActiveDirectory
$ADObject = New-Object Microsoft.ActiveDirectory.Management.ADObject
# No SamAccountName property will be listed
$ADObject | Get-Member
Now, try to reference a non-existing property, like "SamAccountName" (the ADObject extends the ADPropertyValueCollection class which is basically a dictionary, so indexing into it's property is totally valid):
$ADObject["SamAccountName"]
# SamAccountName property will now be listed even though we haven't set it
$ADObject | Get-Member
This is not restricted to AD property names, anything goes:
"1 This","2 Is","3 Quite","4 Funky","5 Isn't","6 It?" |ForEach-Object {
[void]$ADObject[$_]
}
$ADObject |Get-Member

Answer 2

Microsoft.ActiveDirectory.Management.ADObject already have SamAccountName property. You don't need to recreate it. Just need define value for it, like this:
$obj = New-Object Microsoft.ActiveDirectory.Management.ADObject
$obj.SamAccountName = 'AccountName'
$obj | Get-Member
Output:
TypeName: Microsoft.ActiveDirectory.Management.ADObject
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()
ToString Method string ToString()
Item ParameterizedProperty Microsoft.ActiveDirectory.Management.ADPropertyValueCollection Item(string propertyN...
SamAccountName Property Microsoft.ActiveDirectory.Management.ADPropertyValueCollection SamAccountName {get;s...