Merging hashtables

Hash tables in PowerShell are very useful and can be used for a bunch of things. Recently I had to use some code I found on StackOverflow to Merge hash tables. This post is about my experience and the really cool piece of code that iRon posted on StackOverFlow.

First I need to login to azure and find my application:


add-azurermaccount

get-azurermresource

I see my resource in the Get-azureRmresource so now I know that I can query for it’s app settings using this command:


$myapp = Get-AzureRmWebAppSlot -resourcegroupname myresourcegroup -name myresourcename -slot production

This produces and object that contains all my web application settings in azure for my app in question. The item i want to work on is the .siteconfig.AppSettings

This portion of the object will have the properties of the appsettings in the azure blade as shown below:


PS C:\Users\me&amp;gt; $myApp.siteconfig.AppSettings

Name Value

WEBSITE_NODE_DEFAULT_VERSION 6.9.1

Now that I have the current version of what is in my application I now need to see what to do to put new settings in place and not wipe out any existing settings. The cmdlet to do the addition is Set-AzureRmWebAppSlot. After looking through the help I can see that I have a parameter that I can pass for the settings i want called -appSettings. It like most of the other settings require a hash table: [[-AppSettings] <Hashtable>]

So The $myApp.SiteConfig.Appsettings is a list:


$appSettings = $Myapp.siteconfig.appsettings
&amp;nbsp;$appsettings -is [pscustomobject]
False
&amp;nbsp;$appsettings.gettype()

IsPublic IsSerial Name BaseType
-------- -------- ---- --------
True True List`1 System.Object

$appsettings -is [hashtable]
False

This means I need to convert my object from List`1 to a hashtable so I’ll iterate through it and create a hashtable:


$appSettingsHash = @{}
&amp;nbsp;foreach($k in $appSettings) { $appSettingsHash[$k.name] = $k.value }
&amp;nbsp;$appsettingshash

Name Value
---- -----
WEBSITE_NODE_DEFAULT_VERSION 6.9.1

&amp;nbsp;$appsettingshash -is [hashtable]

True

Ok now that I have my current settings in a hashtable I need to now work with entries that I want to add to a hashtable and then post it.


$appSettings ='{"AppSettings:testkey1": "45test","AppSettings:TestId": "This is a Test Key 28"}'

$newAppSettings = $appSettings | convertfrom-json 

$newAppSettingsHash = @{}
 $newAppSettings.psobject.properties | ForEach-Object { $newAppSettingsHash[$_.Name] = $_.Value }

$newappsettingsHash -is [hashtable]
True

This is where the magic of iRon‘s script comes into play. Since I need to use this in a deployment from TFS I created the hashtable in Json Format first and then convert the Json format to a [hashtable]. Then I call iRon’s Script with the $newappSettingsHash and the $appsettingsHash. Now I have a merged hashtable that I can now update my application with.


Function Merge-Hashtables([ScriptBlock]$Operator) {
$Output = @{}
ForEach ($Hashtable in $Input) {
If ($Hashtable -is [Hashtable]) {
ForEach ($Key in $Hashtable.Keys) {$Output.$Key = If ($Output.ContainsKey($Key)) {@($Output.$Key) + $Hashtable.$Key} Else {$Hashtable.$Key}}
}
}
If ($Operator) {ForEach ($Key in @($Output.Keys)) {$_ = @($Output.$Key); $Output.$Key = Invoke-Command $Operator}}
$Output
}

$hashtable = $newAppSettingsHash, $appSettingsHash | Merge-Hashtables {$_[0]} 
$results = Set-AzureRmWebAppSlot -AppSettings $hashtable -name $website -ResourceGroupName $resourceGroup -slot $slot
$r = $results.SiteConfig.AppSettings
Write-Output $r

The really cool thing about the Merging of the hashtables function is that you can merge more than 2 hash tables. See this comment from iRon about how it works:

Full code for this merge hashtable function against a azure application is below:

	param($websitename = 'TEst' ,$resourceGroup = 'SchuTest',$slot = 'production', $appSettings ='{"AppSettings:testkey1": "45test","AppSettings:TestId": "This is a Test Key 28"}')
	#https://stackoverflow.com/questions/8800375/merging-hashtables-in-powershell-how
	Function Merge-Hashtables([ScriptBlock]$Operator) {
	$Output = @{}
	ForEach ($Hashtable in $Input) {
	If ($Hashtable -is [Hashtable]) {
	ForEach ($Key in $Hashtable.Keys) {$Output.$Key = If ($Output.ContainsKey($Key)) {@($Output.$Key) + $Hashtable.$Key} Else {$Hashtable.$Key}}
	}
	}
	If ($Operator) {ForEach ($Key in @($Output.Keys)) {$_ = @($Output.$Key); $Output.$Key = Invoke-Command $Operator}}
	$Output
	}
	try {
	foreach($website in $websiteName)
	{
	ConvertFrom-Json $appSettings –ErrorAction Stop
	#it is expected that the app settings is a string representation of a hashtable that is writtin in Json. So that it can be converted to a powershell hashtable during runtime
	$newAppSettings = $appSettings \| convertfrom-json
	$newAppSettingsHash = @{}
	$newAppSettings.psobject.properties \| ForEach-Object { $newAppSettingsHash[$_.Name] = $_.Value }
	$Application = get-azurermwebappslot –Name $website –ResourceGroupName $resourceGroup –Slot $slot
	$ExistingSettings = $Application.siteconfig.AppSettings
	$appSettingsHash = @{}
	foreach($k in $ExistingSettings)
	{
	$appSettingsHash[$k.name] = $k.value
	}
	#https://stackoverflow.com/questions/8800375/merging-hashtables-in-powershell-how
	$hashtable = $newAppSettingsHash, $appSettingsHash \| Merge-Hashtables {$_[0]}
	$results = Set-AzureRmWebAppSlot –AppSettings $hashtable –name $website –ResourceGroupName $resourceGroup –slot $slot
	$r = $results.SiteConfig.AppSettings
	Write-Output $r
	}
	}
	catch
	{
	Write-Error "$appsettings must be in JSON format"
	}