-AsCustomObject method calls don't actually work about idempotion HOT 1 CLOSED

This turned out to be more complicated than expected. The implementation of -NoValidateSet added in ed54f45 was easy enough, but it exposed a deeper problem with using -AsCustomObject.

Because of the way PowerShell generates a Script Method, my default template will always fail with these methods.

The reason is that the param() block specified in a Script Method is not implemented as such; instead each parameter is created as a local variable and its value is set to whatever the parameter supplied to the method is. This is why the [ValidateSet()] attributes fail too, so it's probably the same logic as a closure or perhaps internally it's just creating a closure.

But what this means is that there's no way inside of the method to programmatically determine what the parameters are; $MyInvocation.MyCommand has an empty .Parameters set.. because there are no parameters, just local variables. This means using $PSBoundParameters and even $args fails.

Because of that, there's no good way to use a templating system like this to dynamically build the [hashtable] that needs to be provided to Invoke-DscResource, because you'd need to know all the parameter names in advance or tease them out from the local variables.

As a result, the entire concept of using -AsCustomObject for what we're doing here is probably useless 99% of the time.

The one instance where I could see it being useful is when you have a very specific custom template definition that knows the parameter names already, so it doesn't need to use dynamic discovery of them. It might supply values for nearly all of them and maybe it uses a few dynamically by direct name.

Behavior Changes

• -NoValidateSet is available for all parameter sets so it can be used for the other modes (not using a custom object) if that's desired.
• When -AsCustomObject is specified, -NoValidateSet is automatically enabled, but it can be overridden with -NoValidateSet:$false if there's some reason for that.
• When -AsCustomObject is specified and the default template is used, the call is allowed, but a warning is emitted explaining that the resulting methods will not work.

from idempotion.