Powershell select parent xml node based on child node value and add child element

Question

see the following xml

    <catalog>
        <books>
           <book id="bk101">
              <author>Gambardella, Matthew</author>
              <title>XML Developer's Guide</title>
              <genre>Computer</genre>
              <price>44.95</price>
              <publish_date>2000-10-01</publish_date>
              <description>An in-depth look at creating applications 
              with XML.</description>
           </book>
           <book id="bk102">
              <author>Ralls, Kim</author>
              <title>Midnight Rain</title>
              <genre>Fantasy</genre>
              <price>5.95</price>
              <publish_date>2000-12-16</publish_date>
              <description>A former architect battles corporate zombies, 
              an evil sorceress, and her own childhood to become queen 
              of the world.</description>
           </book>
           <book id="bk103">
              <author>Corets, Eva</author>
              <title>Maeve Ascendant</title>
              <genre>Fantasy</genre>
              <price>5.95</price>
              <publish_date>2000-11-17</publish_date>
              <description>After the collapse of a nanotechnology 
              society in England, the young survivors lay the 
              foundation for a new society.</description>
           </book>
       </books>
    </catalog>

I want to, in powershell, select the book node/element where the author is Corets,Eva and then add a child element of book, another element(sibling of price, comes directly after price) of , say, length. along with a new value for length of say, '456'

So the (partial) xml code for the book element after Ive run the code would look like:

<catalog>
    <books>
       <book id="bk103">
          <author>Corets, Eva</author>
          <title>Maeve Ascendant</title>
          <genre>Fantasy</genre>
          <price>5.95</price>
          <length>456</length>        
          <publish_date>2000-11-17</publish_date>
          <description>After the collapse of a nanotechnology 
          society in England, the young survivors lay the 
          foundation for a new society.</description>
       </book>
       <book>
        ....
       </book>
    </books>
<etc>

Can anyone assist? Been stuck for two days now. Thanks

Please add the code of what you have tried so far, including any (incorrect) output. — zett42
– zett42, Commented Nov 17, 2021 at 14:45

dugas · Accepted Answer · 2021-11-17 14:54:42Z

2

You can use the XMLNode.InsertAfter method.

Example:

[xml]$books = Get-Content .\books.xml
$corets = $books.catalog.books.book | Where-Object { $_.author -eq 'Corets, Eva' }
$coretsPrice = $corets.SelectSingleNode('price')
$coretsLength = $books.CreateElement('length')
$coretsLength.InnerText = 495
$corets.InsertAfter($coretsLength, $coretsPrice)

answered Nov 17, 2021 at 14:54

dugas

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1 Comment

Keith Over a year ago

I put a thanks comment in here yesterday but for some reason its disappeared. So again, many thanks, works a treat!

Mathias R. Jessen · Accepted Answer · 2021-11-17 14:59:39Z

1

You can use the following XPath expression to select only <book /> nodes where a child node <author> has a text value of Corets, Eva:

//book[author[. = 'Corets, Eva']]

So you could do something like:

# Create a new XML document
$newDocument = [xml]'<catalog><books></books></catalog>'
$newBooks = $newDocument.SelectSingleNode('/catalog/books')

# Loop through all relevant <book> nodes in the existing document
foreach($book in $existingDocument.SelectNodes('//book[author[. = 'Corets, Eva']]')){
    # import book node to new document
    $newBook = $newDocument.ImportNode($book, $true)

    # add new required child node
    $newLength = $newDocument.CreateElement('length')
    $newLength.InnerText = '456'

    # insert new node after `price`
    [void]$newBook.InsertAfter($newLength, $newBook.SelectSingleNode('./price'))
    # insert new book node under /catalog/books
    [void]$newBooks.AppendChild($newBook)
}

answered Nov 17, 2021 at 14:59

Mathias R. Jessen

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1 Comment

Keith Over a year ago

Many thanks Mathias, went with dugas solution as it got here first and worked. But yours looks great also.

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