xQuery update question

Here is my xml

<book asin="0201100886"
  created="128135928"
  lastLookupTime="128135928">
  <price>102.00</price>
  <purchaseDate>2005-01-22</purchaseDate>
</book>

<book asin="0122513363" created="128135600" lastLookupTime="128136224">
  <price>50.95</price>
  <purchaseDate>2005-01-22</purchaseDate>
</book>

<book asin="0201441241"
  created="128136896"
  lastLookupTime="128136896">
  <price>108.20</price>
  <purchaseDate>2005-01-22</purchaseDate>
</book>开发者_StackOverflow


<book asin="0471250600"
  created="128136896"
  lastLookupTime="128136896">
  <price>107.95</price>
  <purchaseDate>2005-01-22</purchaseDate>
</book>

<book asin="0321193628"
  created="128136896"
  lastLookupTime="128136896">
  <price>112.40</price>
</book>

I need to update all the books prices by 0.50 cents. How can I do this?

If you are looking for a solution using XQuery Update Facility:

for $p in //price return
replace value of node $p with $p + 0.50

In XQuery, a recursive function is used to do the transformation.

declare function local:reprice($nodes as node()*) {
  for $node in $nodes
  return
    typeswitch($node)
       case element(price)
          return element price {xs:decimal($node) + 0.5}
       case element(
          return 
            element {name($node)} {
               $node/@*,
               local:reprice($node/node())}
      default
        return $node
 };

then if the books document is referenced as $books:

local:reprice($books)

Further discussion and examples are in http://en.wikibooks.org/wiki/XQuery/Typeswitch_Transformations.

Alternatively, use an XML database such as eXist-db and update insitu:

 for $price in $books//price
 let $newprice := xs:decimal($price) + 0.5
 return update replace $price with elememt price {$newprice}

Note that XQuery update extensions are mainly implementation-dependant until XQuery Update is more widely supported

XSLT is significantly more appropriate to use than XQuery for such kind of tasks:

This transformation:

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output omit-xml-declaration="yes" indent="yes"/>
 <xsl:strip-space elements="*"/>


 <xsl:template match="node()|@*">
  <xsl:copy>
   <xsl:apply-templates select="node()|@*"/>
  </xsl:copy>
 </xsl:template>

 <xsl:template match="price/text()">
  <xsl:value-of select="format-number(. + 0.50, '##0.00')"/>
 </xsl:template>
</xsl:stylesheet>

when applied on the provided XML document:

<books>
    <book asin="0201100886"   created="128135928"   lastLookupTime="128135928">
        <price>102.00</price>
        <purchaseDate>2005-01-22</purchaseDate>
    </book>
    <book asin="0122513363" created="128135600" lastLookupTime="128136224">
        <price>50.95</price>
        <purchaseDate>2005-01-22</purchaseDate>
    </book>
    <book asin="0201441241"   created="128136896"   lastLookupTime="128136896">
        <price>108.20</price>
        <purchaseDate>2005-01-22</purchaseDate>
    </book>
    <book asin="0471250600"   created="128136896"   lastLookupTime="128136896">
        <price>107.95</price>
        <purchaseDate>2005-01-22</purchaseDate>
    </book>
    <book asin="0321193628"   created="128136896"   lastLookupTime="128136896">
        <price>112.40</price>
    </book>
</books>

produces the wanted, correct result:

<books>
   <book asin="0201100886" created="128135928" lastLookupTime="128135928">
      <price>102.50</price>
      <purchaseDate>2005-01-22</purchaseDate>
   </book>
   <book asin="0122513363" created="128135600" lastLookupTime="128136224">
      <price>51.45</price>
      <purchaseDate>2005-01-22</purchaseDate>
   </book>
   <book asin="0201441241" created="128136896" lastLookupTime="128136896">
      <price>108.70</price>
      <purchaseDate>2005-01-22</purchaseDate>
   </book>
   <book asin="0471250600" created="128136896" lastLookupTime="128136896">
      <price>108.45</price>
      <purchaseDate>2005-01-22</purchaseDate>
   </book>
   <book asin="0321193628" created="128136896" lastLookupTime="128136896">
      <price>112.90</price>
   </book>
</books>