JScript.NET: Enumerating WMI collections - collections

Question

In JScript.NET the following snippet:
wmi.js
------
var wmi = GetObject("winmgmts:{impersonationLevel=impersonate}!\\\\.\\root\\cimv2"),
col =null, prc=null;
col=wmi.ExecQuery("SELECT * From Win32_Process", "WQL", 32);
//col=wmi.InstancesOf("Win32_Process");
var e = new Enumerator(col);
for (; !e.atEnd(); e.moveNext()){
prc = e.item();
print(prc.CommandLine);
}
compiles with:
%windir%\Microsoft.NET\Framework64\v4.0.30319\jsc.exe /platform:x64 wmi.js
and executes, but changing the WMI call with:
col=wmi.ExecQuery("SELECT * From Win32_Process", "WQL", 32);
compilation still works, while the execution gives the:
Unhandled Exception: System.InvalidCastException:
Unable to cast COM object of type 'System.__ComObject' to interface type 'System.Collections.IEnumerable'.
This operation failed because the QueryInterface call on the COM component for the interface with IID '{496B0ABE-CDEE-11D3-88E8-00902754C43A}' failed due to the following error:
'No such interface supported (Exception from HRESULT: 0x80004002
I don't understand why, since for both
InstancesOf
and
ExecQuery documentation says:
If successful, the method returns an SWbemObjectSet
Also, WSH JScript can enumerate both InstancesOf collection and ExecQuery.

Answer 1

First things first, remove the flag for wbemFlagForwardOnly and the ExecQuery returns an object that works as expected.
var wmi = GetObject("winmgmts:{impersonationLevel=impersonate}!\\\\.\\root\\cimv2")
, col =null, prc=null;
col=wmi.ExecQuery("SELECT * From Win32_Process");
//col=wmi.InstancesOf("Win32_Process");
var e = new Enumerator(col);
for (; !e.atEnd(); e.moveNext()){
prc = e.item();
print(prc.CommandLine);
}
For the explanation, here's a shot in the dark (I don't work with Jscript.NET every day nor am I an expert).
from https://msdn.microsoft.com/en-us/library/ms974547.aspx:
"A forward-only enumerator performs much faster than the default enumerator, because WMI doesn't maintain references to objects in the SWbemObjectSet"
from the error:
"Unable to cast COM object of type 'System.__ComObject' to interface type 'System.Collections.IEnumerable."
It seems that converting collection to enumerator requires a reference to the object being casted. With wbemFlagForwardOnly flag, there is no reference passed so cast fails.
That is how I read this. Take it for what it's worth.
An interesting thing I found when researching: there is no error with this enumerator using wscript/cscript versus executing exe from jsc/csc.
Also, it seems VBScript has no problem enumerating with these flags; check out the examples and compare - https://msdn.microsoft.com/en-us/library/ms525775(v=vs.90).aspx.