PowerShell 两个参数中的任何一个都可以为空，但不能同时为空答案

【问题标题】：PowerShell two parameters either of them can be null but not both nullPowerShell 两个参数中的任何一个都可以为空，但不能同时为空
【发布时间】：2017-06-07 15:29:10
【问题描述】：

我想知道这是否可以在参数级别而不是在代码中完成：我有 2 个参数：$School 和 $Class

Get-Students -School SchooName # Will give me all Students name in all classes in that School
Get-Students -Class ClassName  # Will give me all Students name in that Class across all schools
Get-Students                   # Should return parameter level error.

我尝试使用以下内容：

function Get-Students{
param(
    [parameter(ParameterSetName="School no null")]
    [ValidateNotNullOrEmpty()]
    [string]$School,
    [parameter(ParameterSetName="School no null")]
    [AllowNull()]
    [string]$Class,
    [parameter(ParameterSetName="Class no null")]
    [AllowNull()]
    [string]$School,
    [parameter(ParameterSetName="Class no null")]
    [ValidateNotNullOrEmpty()]
    [string]$Class
)
}

但是这样不行……

希望我正确地解释了这一点。或者如果没有办法仅在代码内部从参数执行此操作？

谢谢河流

【问题讨论】：

标签： validation powershell parameters null

【解决方案1】：

更新。以下注释代码 sn-p 基于Add a parameter to multiple Parameter Sets 文章。允许同时提供-Class 或-School 参数或两者。

function Get-Students{
param(
    [parameter(Mandatory=$false)][switch]$SomeThing, # any type instead of [switch]
    # ↑↑↑ parameter(s) in all Parameter Sets

    [parameter(Mandatory=$true,  ParameterSetName="School No Null")]
    [parameter(Mandatory=$true,  ParameterSetName="Class And School")]
    [ValidateNotNullOrEmpty()]
    [string]$School,

    [parameter(Mandatory=$true,  ParameterSetName="Class No Null")]
    [parameter(Mandatory=$true,  ParameterSetName="Class And School")]
    [ValidateNotNullOrEmpty()]
    [string]$Class
)
    Write-Host $PsCmdlet.ParameterSetName -ForegroundColor Cyan
    switch ($PsCmdlet.ParameterSetName) 
    { 
        "School No Null"   { "$School/*,$($SomeThing.IsPresent)"; break} 
        "Class No Null"    { "*/$Class,$($SomeThing.IsPresent)";  break}
        "Class And School" { "$School/$Class,$($SomeThing.IsPresent)";  break}
    }
}
Get-Students -Class "A"
Get-Students -School "West" -SomeThing
Get-Students -Class "A" -School "West"

### errors raised:
#   Get-Students
### Parameter set cannot be resolved using the specified named parameters.
### + FullyQualifiedErrorId : AmbiguousParameterSet,Get-Students
#   Get-Students -Class ""
#   Get-Students -School ""
### Cannot validate argument on parameter '…'. The argument is null or empty.
### + FullyQualifiedErrorId : ParameterArgumentValidationError,Get-Students

原始答案（代码 sn-p 基于 PowerShell 团队博客中的 PowerShell V2: ParameterSets 文章 和 MSDN help article）不允许 同时提供 both -Class 和 -School 参数：

function Get-Students{
param(
 [parameter(Mandatory=$true,  ParameterSetName="School No Null")][ValidateNotNullOrEmpty()]
 [parameter(Mandatory=$false, ParameterSetName="Class No Null")] #[AllowNull()]
 [string]$School,

 [parameter(Mandatory=$true,  ParameterSetName="Class No Null")] [ValidateNotNullOrEmpty()]
 [parameter(Mandatory=$false, ParameterSetName="School No Null")]#[AllowNull()]
 [string]$Class
)
    Write-Host $PsCmdlet.ParameterSetName -ForegroundColor Cyan
    switch ($PsCmdlet.ParameterSetName) 
    { 
        "School No Null" { $School; break} 
        "Class No Null"  { $Class;  break}
    }
}

### valid calls:

Get-Students -Class "A"
Get-Students -School "West"

### errors raised:
### Parameter set cannot be resolved using the specified named parameters.
# Get-Students
# Get-Students -Class "A" -School "West"
### The argument is null or empty.
# Get-Students -Class ""
# Get-Students -School ""

【讨论】：

非常感谢！我认为这是正确的答案！这意味着变量应该只出现一次，但参数条件不同！

【解决方案2】：

您可以在代码中测试它们，而不是尝试将此检查填充到参数集中。

if ($School -eq $null -and $Class -eq $null) {throw "School and Class must not be null together!"}

【讨论】：