ValidateSet should support a dynamically generated set

People often use dynamic parameters so they can dynamically generate a ValidateSet attribute.

We should provide a simpler way to do this. One option is to accept a scriptblock:

param(
    [ValidateSet( { Get-ChildItem -ah | ForEach-Object Name } )]
    $HiddenFileName
)

Jason Shirk (@lzybkr)

This is a much better solution. Well played Jason Shirk (@lzybkr) like it!

We should also consider binary cmdlets. One option is to accept a type that implements an interface, something like:

public interface IValidateSetGenerator
{
    IEnumerable<string> Get();
}
public class MyValidateSetGenerator : IValidateSetGenerator
{
    public IEnumerable<string> Get()
    {
        yield return "Something";
    }
}
...
    [Parameter()]
    [ValidateSet(typeof(MyValidateSetGenerator)]
    public string Something { get; set; }

This could probably work in PowerShell too (the interface would be defined in System.Management.Automation.dll.

I think we'd need a way of passing $PSBoundParameters to truly cover most of the scenarios where people are resorting to dynamic parameters today.

Recently I played with this and it seems like it might be too expensive due to IntelliSense.

Ilya (@iSazonov)

Ilya (@iSazonov) What is to expensive?

Staffan Gustafsson (@powercode)

Staffan Gustafsson (@powercode) IntelliSense can call attributes very often. ValidateSet with script block becomes similar to ValidateScript (can run unpredictably long).

Perhaps we should do only IValidateSetGenerator (not script block) because we want support interfaces in PowerShell classes.

Also could we add IValidateSetGenerator not only in ValidateSet attribute: ValidateScript, ValidatePattern, ... for IntelliSense support?

Ilya (@iSazonov)

Ilya (@iSazonov) I don't think that would be much of a problem. Most people know not to have long-running commands in intellisense code. People are already working around this issue using the less-friendly dynamicparam block and passing a ValidateSetAttribute to the attribute collection.

I feel the problem with using an interface for this is that a lot of PowerShell coders aren't programmers. It's one thing to support classes, it's another thing to force the user to use them. Just my opinion ofc. The 'PowerShell way' here is to support a ScriptBlock.

Jason Shirk (@lzybkr) would the following not be easier:

public interface IValidateSetGenerator
{
    IEnumerable<string> Get();
}
public class MyValidateSetGenerator : IValidateSetGenerator
{
    public IEnumerable<string> Get()
    {
        yield return "Something";
    }
}

[Parameter()]
[ValidateSet(MyValidateSetGenerator)]
public string Something { get; set; }

and just have a ValidateSet overload that takes in an IValidateSetGenerator, rather than using typeof?

So two new overloads for ValidateSetAttribute:

ValidateSetAttribute(ScriptBlock sb)

and

ValidateSetAttribute(IValidateSetGenerator g)

IValidateSetGenerator vs IValidateSetEnumerator ?

Ilya (@iSazonov)

Ilya (@iSazonov) maybe even IDynamicValidateSet?

Edit: Upon reflection I prefer IValidateSetEnumerator

It looks like it is from DynamicParams but it is not related directly. Also we have RFC for Dynamic Keywords so we should avoid "Dynamic" term to eliminate confusion.

Liam (@lfshr)

Liam (@lfshr) - C# requires typeof(MyValidateSetGenerator) because MyValidateSetGenerator is not an expression.

The interface name should probably not end in Enumerator because the interface does not define an enumerator.

Maybe IValidateSetValuesGetter

Is this still up for grabs? I'm looking for something small to start with.

update: never mind, I see the PR is in progress :)

Welcome to code review!

maybe you can help me out with my challange. I like to set ValidateSet to run my "example.ps1 -region eu-cental-1" and get the AWS regions

Eg:
Param(
[parameter(Mandatory=$true)]
[ValidateSet((Get-AWSRegion).region)]
[String[]]
$region
)

process {
# do whatever
}

I don't see any link to the relevant PR, but it appears to need a script block, so you would write:

[ValidateSet({ (Get-AwsRegion).Region })]

you're right; it's not a PR; just a little script to automate my AWS stuff. Maybe I open one once it has some relevant features.

[ValidateSet({ (Get-AwsRegion).Region })]

this does not make any difference unfortunately

Jason Shirk (@lzybkr)

Jason Shirk (@lzybkr) a PR is mentioned in this thread, but I don't see any links to it. Did this end up getting implemented?

You need to implement IValidateSetValuesGenerator. See:
https://github.com/iSazonov/PowerShell/blob/65349de2b25022092213d86cfc1f5dfe0c92cbc6/test/powershell/Language/Classes/Scripting.Classes.Attributes.Tests.ps1#L273

@rafaelc81 see here for the example that was merged into documentation after the PR was merged.

https://github.com/PowerShell/PowerShell-Docs/pull/3133/files?short_path=8b392e6#diff-8b392e69e97629458a3c80ee54386057

The example in the docs looks nothing like the example the OP of this issue wanted. The OP asks for a script block, and the solution provided is a full on syntax-verbose class.

I can't get an example like the script block to work. Was that implemented or only the syntax-verbose class version?

If not, are there any plans to support the significantly more terse syntax? Should another issue be opened?

Thanks!

Josh Olson (@OlsonDev)

Josh Olson (@OlsonDev) The issue description is misleading. We only implemented a variant based on IValidateSetValuesGenerator interface until we receive more feedback. Feel free open new issue with the description of the necessary feature.

Indeed. It should be possible to borrow portions of the code from [ArgumentCompleter()] for this purpose; it also takes a script block and apparently applies it to the method defined in IArgumentCompleter

Rain Sallow (/u/ta11ow) (@vexx32)

Rain Sallow (/u/ta11ow) (@vexx32) There is samples in attributes.cs file how to use execution context. I assume that the tests will be most of this work and not the code itself. :-)

Ilya (@iSazonov)

Ilya (@iSazonov) Rain Sallow (/u/ta11ow) (@vexx32) Thanks, I created the aforementioned issue here.

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ValidateSet should support a dynamically generated set #3744

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ValidateSet should support a dynamically generated set #3744

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lfshr commented on May 9, 2017

lzybkr commented on May 9, 2017

iSazonov commented on May 9, 2017

powercode commented on May 9, 2017

iSazonov commented on May 10, 2017

lfshr commented on May 10, 2017

lfshr commented on May 10, 2017

iSazonov commented on May 10, 2017

lfshr commented on May 10, 2017

iSazonov commented on May 10, 2017

lzybkr commented on May 10, 2017

iSazonov commented on May 10, 2017

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oising commented on May 31, 2017

iSazonov commented on Jun 1, 2017

lordisp commented on Nov 3, 2018

vexx32 commented on Nov 3, 2018

lordisp commented on Nov 3, 2018

vexx32 commented on Nov 3, 2018

iSazonov commented on Nov 4, 2018

vexx32 commented on Nov 4, 2018

OlsonDev commented on Jan 14, 2019

iSazonov commented on Jan 15, 2019

vexx32 commented on Jan 15, 2019

iSazonov commented on Jan 15, 2019

OlsonDev commented on Jan 15, 2019

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