Determine XML Node Exists

Question

This is probably simple, but I'm trying to determine if a node exists in an XML document. I thought I found an answer in this post, How to check whether a node exists or not using powershell without getting exception?, but I didn't get it to work. This is my latest attempt.

foreach ($vendor in $xml.Vendors.Vendor| Where-Object  {$_.Type -match "Send"}) {
    $NodeExists = $vendor.SelectSingleNode($vendor.EncKey)
    if ($NodeExists -ne $null) {
        # Do something
    }
    else {
       # something else
    }
   }

Any help would be greatly appreciated.

EDIT: Here is XML from my test file. I need to find out of EncKey exists or note for each vendor.

<?xml version="1.0" encoding="UTF-8"?>
    <!-- Vendors we will send and retreive files from Get-Send means we will get a file and send them a file Send means we will only send them a file-->
    <Vendors>
        <Vendor Type="Get-Send">
            <Name>Vendor1</Name>            
            <RemotePath>/Remote/Path1/</RemotePath>
            <EncKey>pgpenc.key</EncKey>
        </Vendor>
        <Vendor Type="Send">
            <Name>Vendor2</Name>            
            <RemotePath>/Remote/Path2/</RemotePath> 
            <!-- This one has no EncKey -->         
        </Vendor>
    </Vendors>

Solution 1

It appears that I was using the wrong syntax for SelectSingleNode. Here is a working example.

[xml]$xml = @'
<?xml version="1.0" encoding="UTF-8"?>
    <!-- Vendors we will send and retreive files from Get-Send means we will get a file and send them a file Send means we will only send them a file-->
    <Vendors>
        <Vendor Type="Get-Send">
            <Name>Vendor1</Name>            
            <RemotePath>/Remote/Path1/</RemotePath>
            <EncKey>pgpenc.key</EncKey>
        </Vendor>
        <Vendor Type="Send">
            <Name>Vendor2</Name>            
            <RemotePath>/Remote/Path2/</RemotePath> 
            <!-- This one has no EncKey -->         
        </Vendor>
    </Vendors>
'@

foreach ($vendor in $xml.Vendors.Vendor| Where-Object  {$_.Type -match "Send"}) {
    $NodeExists = $vendor.SelectSingleNode("./EncKey")
    if ($NodeExists -ne $null) {
        write-host "EncKey is null"
    }
    else {
       write-host "EncKey is not null"
    }
   }

EncKey is null
EncKey is not null

Thanks everyone for your help.

Solution 2

The easiest way I can think of is to try to write the node value to a variable, and then to see if that variable is null. Here's an example with the standard bookstore xml file.

[xml]$bookstore = Get-Content .\bookstore.xml
foreach ($book in $bookstore.bookstore.book | Where-Object {$_.Type -match "novel"}) {
 $NodeExists = $book.author
 if($NodeExists){
  Write-Host $book.author
 }
 else{
  Write-Host 'No Author'
 }
} 

So for your script, I would think it might be

$NodeExists = $null
foreach ($vendor in $xml.Vendors.Vendor| Where-Object  {$_.Type -match "Send"}) {
 $NodeExists = $vendor.EncKey
 if ($NodeExists) {
  # Do something
 }
 else {
  # something else
  }
}

Solution 3

Provided you load the $xml object as an XmlDocument using

$xml = new-object System.Xml.XmlDocument
$xml.LoadXml( (get-content $pathToXmlFile) )

Then you can do this, which is much simpler:

if ($vendor.encKey -ne $null) {
  # does exist
} else {
  # does not exist
}

Solution 4

Use XPath to select matching nodes. InnerText is searchable by text(). You can use where-object, or ? too; behaviour is a bit different. Without sample XML it's hard to be more precise. Use XPath like so,

[xml]$doc = @'
<root>
<Vendors>
<Vendor>
<Type>Send</Type>
</Vendor>
<Vendor>
<Type>Receive</Type>
</Vendor>
</Vendors>
</root>
'@

# Xpath query will return a NodeList, even if no match is found
$node1 = $doc.SelectNodes("//Vendor/Type[text() = 'Send']")
$node2 = $doc.SelectNodes("//Vendor/Type[text() = 'Sent']")
$node1.Count
1
$node2.Count
0

# where-object will return $null if no match is found
$node1 = $doc.SelectNodes("//Vendor/Type") | ? { $_.InnerText -eq "Send" }
$node2 = $doc.SelectNodes("//Vendor/Type") | ? { $_.InnerText -eq "Sent" }

$node1 -eq $null
False
$node2 -eq $null
True

View more solutions

Comments

[Victor Zakharov]

Could you please provide a reduced test case for your issue? Something we can paste into our favorite Powershell editor and play with it?

[mack]

Thanks Alex. This is along the lines of what I was attempting to do, but if $vendor.EncKey does not exists I get an exception: Property 'EncKey' cannot be found on this object. Make sure that it exists. and I never get to the "else" part of the statement.

[Jay]

You can shorten this with "if ( $vendor.EncKey ) {" -- also, this is case insensitive, as compared to SelectSingleNode which did not work for me. I did not have any exception issue with this.

[Jay]

According to my tests, SelectSingleNode is case sensitive, unless there is a way to change its behavior.

[LosManos]

Downvote because if the element does not exist an exception is thrown.

[laika]

@mack you'll actually get an exception when you have strict mode turned on. When the strict mode is turned off, then $vendor.EncKey evaluates to $false in the statement if ( $vendor.EncKey ), as provided by @Jay

[Raf]

Good, but should be opposite. if ($NodeExists -ne $null) { write-host "EncKey is NOT null" }

[kalenwatermeyer]

An excellent article which simplifies the SelectSingleNode(..) implementation, using XML namespaces: https://blog.danskingdom.com/powershell-functions-to-get-an-‌​xml-node-and-get-and‌​-set-an-xml-elements‌​-value-even-when-the‌​-element-does-not-al‌​ready-exist/