Written by: Karl Prosser
6/17/2008 9:08 PM

Based on the performance testing and work being done by myself , mow , Brandon Shell and others the question has come up what is the quickest way to generate a PSCustomObject, whether in script , on in C#, and how do you even do it in C#?

Some typical ways of doing in PowerShell have been either something like the following trick:

or with using the Add-member cmdlet as below:

$a = 1 | select a , b , c , d

$a | add-member -membertype noteproperty -name status -value done

however both are really slow. There is another way to do it in script, and that is directly with the PSobject, but still PowerShell (especially version 1) has a huge overhead when creating new objects with new-object but below is an example none the less.

$obj = new-Object system.Management.Automation.PSObject

$note = new-object System.Management.Automation.PSnoteproperty "karl" , "a value"

$obj.psobject.members.add( $note );

But if you really want to do speed, or if you have need to generate these objects in a cmdlet regardless of speed here is how you can do it in C#.

public static PSObject newPsCustomObject2()

{

//Creating a PSobject without any parameters in the constructor creates a PSCustomObjectg

PSObject obj = new PSObject();

//PSNoteProperties are not strongly typed but do contain an explicit type.

obj.Properties.Add(new PSNoteProperty("age",24));

obj.Properties.Add(new PSNoteProperty("name","jon"));

//Alias allow you to cast one property as another as well as just plain aliasing

obj.Properties.Add(new PSAliasProperty("ageasstring","age",typeof(string)));

return obj;

}

Some notes about the above, I didn't show how you could add ScriptProperties or ScriptMethods yet as I wanted to keep it simple and not cover creating scriptblocks. Before I go lets performance test this baby compared to creating this in pure PowerShell.

So in the:

1) first corner we have creating the object with select-object, then setting the properties.(but we can't set the alias)
2) Creating the object with new-object, then using add-member to add all the properties.
3) calling our static method above.

#select-object version

for($i = 0;$i -lt 50000;$i++) { $a = 1 |Select-Object age, name; $a.age = 24; $a.name = "john" }

#add-member version

for($i = 0;$i -lt 50000;$i++)

{ $a = new-Object psobject;

$a | add-member -membertype noteproperty -name age -value 24

$a | add-member -membertype noteproperty -name name -value "john"

$a | add-member -membertype aliasproperty -name "ageasstring" -value "age" -secondvalue "string"

}

#Our fast version

for($i = 0;$i -lt 50000;$i++) { $a = [snapinini.newobjecthelper]::newPsCustomObject2(); }

so we are creating 50,000 objects and the results are.

and i used to complain with the performance hit of a address lookup for a method in a C++ virtual method table!!

at worst the official add-member technique is over 60 times slower than calling C#, and thats not really RAW C#, thats still powershell invoking a C# method 50,000 times, and powershell managing a loop.

if fact just to test i added another test

$a = [snapinini.newobjecthelper]::newPsCustomObject3();

where newPSCustomObject3() moves the 50,000 loop to inside C#.. and here the speed is 0.95 seconds, so about half the speed of invoking the C# method from powershell each time - this speed difference I am happy with though. The PowerShell team seem to have done a good job of invoking C# methods quickly.

Another day I should investigate the speed of creating objects that have been created with the extended type system.

I'd love if somebody can run these tests in v2.

Also sometime soon I shall share a helper function you can use to quickly generate a PScustomObject with properties and values you specify in script.

-Karl

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