如何在PowerShell中访问嵌套的JSON字段

我正在try 访问由Azure Advisor使用PowerShell创建的JSON对象中的特定字段.我有以下对象:

@{id=/subscriptions/xxxx/providers/Microsoft.Advisor/recommendations/xxxx;
category=Cost;
impact=High;
impactedArea=Microsoft.Subscriptions/subscriptions;
description=Consider virtual machine reserved instance to save over your on-demand costs;
recommendationText=Consider virtual machine reserved instance to save over your on-demand costs;
recommendationTypeId=xxx; instanceName=xxxx;
additionalInfo=;
tags=;
ResourceId=/subscriptions/xxxx/providers/Microsoft.Advisor/recommendations/xxxx}

在这里，我想访问一个字段‘avingsCurrency’，以便在if语句中进行比较.该字段嵌套在‘addtionalInfo’中，而后者又嵌套在‘visorRecommendation’对象中.

我现在有以下代码:

Write-Output "advisorrecommendation: $advisorRecommendation"

if (-not([string]::IsNullOrEmpty($advisorRecommendation.additionalInfo)))
{
    $additionalInfo = $advisorRecommendation.additionalInfo | ConvertTo-Json
    Write-Output "additionalInfo: $additionalInfo"
    if (-not([string]::IsNullOrEmpty($additionalInfo.savingsCurrency)))
    {
        $savingsCurrency = $additionalInfo.savingsCurrency | ConvertTo-Json
        Write-Output "Currency: $savingsCurrency"
    }
}
else
{
    $additionalInfo = $null
}

此代码给出以下输出:

advisorrecommendation:
@{id=/subscriptions/xxxx/providers/Microsoft.Advisor/recommendations/xxx; category=Cost; impact=High; impactedArea=Microsoft.Subscriptions/subscriptions; description=Consider virtual machine reserved instance to save over your on-demand costs; recommendationText=Consider virtual machine reserved instance to save over your on-demand costs; recommendationTypeId=xxxx; instanceName=xxxx; additionalInfo=; tags=; ResourceId=/subscriptions/xxxx/providers/Microsoft.Advisor/recommendations/xxxx}

additionalInfo: {
    "annualSavingsAmount": "697",
    "reservedResourceType": "virtualmachines",
    "targetResourceCount": "4",
    "savingsCurrency": "USD",
    "savingsAmount": "58",
    "lookbackPeriod": "30",
    "displaySKU": "Standard_B2s",
    "displayQty": "4",
    "location": "westeurope",
    "region": "westeurope",
    "vmSize": "Standard_B2s",
    "subId": "xxxx",
    "scope": "Single",
    "term": "P1Y",
    "qty": "4",
    "sku": "Standard_B2s"
}

尽管我可以清楚地看到‘addtionalInfo’中的字段不是空的或空的，但‘avingsCurrency’字段从不通过NULL/Empty判断.这里出了什么问题？如果我不使用前面的存在性判断来try 打印，它只会打印附加了.avingsCurrency的添加信息对象，如下所示:

savingsCurrency: {
    "annualSavingsAmount": "697",
    "reservedResourceType": "virtualmachines",
    "targetResourceCount": "4",
    "savingsCurrency": "USD",
    "savingsAmount": "58",
    "lookbackPeriod": "30",
    "displaySKU": "Standard_B2s",
    "displayQty": "4",
    "location": "westeurope",
    "region": "westeurope",
    "vmSize": "Standard_B2s",
    "subId": "xxxx",
    "scope": "Single",
    "term": "P1Y",
    "qty": "4",
    "sku": "Standard_B2s"
}.savingsCurrency