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adds PSTypeName post appendix (#16)

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content/posts/pstypename/index.md
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@ -5,9 +5,8 @@ date: 2022-03-16T09:24:56+01:00
categories: ['PowerShell']
tags: ['parameter', 'validation', 'PSTypeName']
# lastmod: 2022-03-16T09:24:56+01:00
# showDateUpdated: true
lastmod: 2022-03-22T09:00:00+01:00
showDateUpdated: true
# custom overrides for pages
# showDate: false
# showAuthor: false
@ -97,7 +96,8 @@ function Invoke-Launch {
}
```
This common pattern could fail whenever someone changes your object properties. If the _LengthInMeter_ property is missing you ran into an error. E.g.:
This common pattern could fail whenever someone changes your object properties. If the _LengthInMeter_ property is
missing you ran into an error. E.g.:
```console
> $Rocinante = [PSCustomObject]@{ foo = 'bar' }
@ -105,10 +105,12 @@ This common pattern could fail whenever someone changes your object properties.
```
{{< note >}}
Keep in mind - Because we are using here custom objects and not class instances, we can not use `Rocinante` as a parameter type like `[Rocinante]$Ship` which would solve this immediately.
Keep in mind - Because we are using here custom objects and not class instances, we can not use `Rocinante` as a
parameter type like `[Rocinante]$Ship` which would solve this immediately.
{{< /note >}}
To fix this we can use the `[PSTypeName()]` parameter attribute, to ensure an object with the correct type name is used. This doesn't verify your parameters but minimize the risk for using invalid parameter objects.
To fix this we can use the `[PSTypeName()]` parameter attribute, to ensure an object with the correct type name is
used. This doesn't verify your parameters but minimize the risk for using invalid parameter objects.
## 🛡️ PSTypeName Usage
@ -164,7 +166,8 @@ function Invoke-Launch {
param (
[Parameter(Mandatory = $true)]
[ValidateNotNullOrEmpty()]
[PSTypeName('Ship.Corvette.LightFrigate')]$Ship
[PSTypeName('Ship.Corvette.LightFrigate')]
[PSCustomObject]$Ship
)
begin {}
@ -236,3 +239,64 @@ function New-LightFrigate {
$Rocinante = New-LightFrigate -Name 'Rocinante' -Registry 'DE-MB2' -HullNumber '158'
```
## 📌 Appendix
Functions using the `[PSTypeName()]` validation should still define a parameter type. I've added the
`[PSCustomObject]` type for the _Ship_ parameter in _Invoke-Launch_.
You can also use a PSCustomObject collection in combination with `[PSTypeName()]` as function parameter:
```powershell
function Invoke-Launch {
[CmdletBinding()]
param (
[Parameter(Mandatory = $true, ValueFromPipeline = $true)]
[ValidateNotNullOrEmpty()]
[PSTypeName('Ship.Corvette.LightFrigate')]
[PSCustomObject[]]$Ship
)
begin {
$DockLength = 50
}
process {
foreach ($i in $Ship) {
if ($Ship.LengthInMeter -gt $DockLength) {
Write-Error -Message "Ship doesn't fit in the docking station." -ErrorAction 'Stop'
}
Write-Information -MessageData ('Launching Ship 🎇🚀 {0} ({1}) ...🪐' -f $i.Name, $i.Registry ) -InformationAction 'Continue'
}
}
end {}
}
```
```bash
# Creating our ship objects.
> $Rocinante = New-LightFrigate -Name 'Rocinante' -Registry 'DE-MB2' -HullNumber '158'
> $XWing = New-LightFrigate -Name 'XWing1' -Registry 'DE-XW1' -HullNumber '43'
# Adding an invalid ship object for testing the validation.
> $InvalidShip = [PSCustomObject]@{ Name = 'Invalid'}
# Creating our ship collection.
> $LaunchGroup = @($Rocinante, $XWing, $InvalidShip)
# Calling Invoke-Launch with named parameter binding.
# An invalid array item blocks running the script for all other items. This is caused by the validation which runs
# prior the execution.
> Invoke-Launch -Ship $LaunchGroup
Invoke-Launch: Cannot bind argument to parameter 'Ship', because PSTypeNames of the argument do not match the
PSTypeName required by the parameter: Ship.Corvette.LightFrigate.
# Calling Invoke-Launch with passing the parameter from pipeline.
# This ensures processing the valid items.
> $LaunchGroup | Invoke-Launch
Launching Ship 🎇🚀 Rocinante (DE-MB2) ...🪐
Launching Ship 🎇🚀 XWing1 (DE-XW1) ...🪐
Invoke-Launch: The input object cannot be bound to any parameters for the command either because the command does
not take pipeline input or the input and its properties do not match any of the parameters that take pipeline input.
```