nested loop through xml-nodes using powershell

Question

I would like to extract from a xml-file the value of the name-attributes from all window- and all viewpoint-nodes.

<?xml version='1.0' encoding='utf-8' ?>
        <workbook>
            <windows>
                <window class='dashboard' name='D1'>
                  <viewpoints>
                    <viewpoint name='V1'> </viewpoint>
                    <viewpoint name='V2'> </viewpoint>
                    <viewpoint name='V3'> </viewpoint>
                </viewpoints>
                </window>
                <window class='dashboard' name='D2'>
                  <viewpoints>
                    <viewpoint name='V10'> </viewpoint>
                    <viewpoint name='V11'> </viewpoint>
                  </viewpoints>
                 </window>
            </windows>
        </workbook>

This is the code I have written:

[XML]$doc = get-content -path 'W:\Demo1.xml'


$objs = @()
$dashboards = $doc.SelectNodes("//window[@class = 'dashboard']")

foreach ($dashboard in $dashboards)
{
   $worksheets = $dashboard.SelectNodes("//viewpoint[@name]")

    foreach ($worksheet in $worksheets)
    {
        $obj = new-object psobject -prop @{Dashboard=$dashboard.name; Worksheet = $worksheet.name}; 
        $objs += $obj;

    }  
 } 

$objs

What I expected:

dashboard   worksheet   
D1          V1
D1          V2
D1          V3
D2          V10
D2          V11

What I got:

dashboard   worksheet   
D1          V1
D1          V2
D1          V3
D1          V10
D1          V11
D1          V14
D2          V1
D2          V2
D2          V3
D2          V10
D2          V11
D2          V14

What is wrong here? The result is completely contradictory to my understanding of how a nested loop works.

Keith Hall · Accepted Answer · 2016-05-19 07:00:58Z

2

An XPath starting with a / character means that it will be begin at the document root node. To create a relative XPath from the context node, you need to put a . before the /.

So your code should be:

[XML]$doc = get-content -path 'W:\Demo1.xml'


$objs = @()
$dashboards = $doc.SelectNodes("//window[@class = 'dashboard']")

foreach ($dashboard in $dashboards)
{
   $worksheets = $dashboard.SelectNodes(".//viewpoint[@name]")

    foreach ($worksheet in $worksheets)
    {
        $obj = new-object psobject -prop @{Dashboard=$dashboard.name; Worksheet = $worksheet.name}; 
        $objs += $obj;

    }  
 } 

$objs

answered May 19, 2016 at 7:00

Keith Hall

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1 Comment

Nylix Over a year ago

You saved my day. Thank you. I spend hours to find the error and it's only a little dot missing......

Martin Brandl · Accepted Answer · 2016-05-19 07:19:32Z

1

You could also simplify that and adopt your xpath to select all viewpoint nodes from dashboard window:

[XML]$doc = get-content -path 'W:\Demo1.xml'

$objs = @()
$worksheets = $doc.SelectNodes("//window[@class = 'dashboard']//viewpoint[@name]")

foreach ($worksheet in $worksheets)
{
    $obj = new-object psobject -prop @{Dashboard=$worksheet.ParentNode.ParentNode.name; Worksheet = $worksheet.name}; 
    $objs += $obj;
}  

$objs

And here a solution without xpath:

[XML]$doc = get-content -path 'W:\Demo1.xml'

$objs = $doc.DocumentElement.windows.window | Where class -eq 'dashboard' | foreach {
    $dashboardName = $_.name
    $_.viewpoints.viewpoint | foreach {
        new-object psobject -prop @{Dashboard=$dashboardName; Worksheet = $_.name}
    }
}

edited May 19, 2016 at 7:19

answered May 19, 2016 at 7:03

Martin Brandl

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4 Comments

Martin Brandl Over a year ago

Upps, you are right - I fixed my answer (now using ParentNode properties to get the dashboard). I will also provide you an example without xpath in a min.

Nylix Over a year ago

Hmm, the line $worksheets = $doc.SelectNodes("//window[@class = 'dashboard']//viewpoint[@name]") produces an error. (translated from german: it's not possible, to invoke a method for an expression having the value NULL)

Nylix Over a year ago

@jisaak: thank you for your second piece of code. I just tried it out. For whatever reason it returns nothing. :-(

Martin Brandl Over a year ago

I omit the $objs that prints the result, I only assign the result to it. Just write $objs in the last line and you will see the output.

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