XQuery: why does this transform modify the source document?

Question

I'm working with this very simple XML doc (that I borrowed from a tutorial), books-mod.xml:

<?xml version="1.0" encoding="ISO-8859-1"?>

<bookstore>

<book category="COOKING">
  <title lang="en">Everyday Italian</title>
  <author>Giada De Laurentiis</author>
  <year>2005</year>
  <price>30.00</price>
</book>

<book category="CHILDREN">
  <title lang="en">Harry Potter</title>
  <author>J K. Rowling</author>
  <year>2005</year>
  <price>29.99</price>
</book>

<book category="WEB">
  <title lang="en">XQuery Kick Start</title>
  <author>James McGovern</author>
  <author>Per Bothner</author>
  <author>Kurt Cagle</author>
  <author>James Linn</author>
  <author>Vaidyanathan Nagarajan</author>
  <year>2003</year>
  <price>49.99</price>
</book>

<book category="WEB">
  <title lang="en">Learning XML</title>
  <author>Erik T. Ray</author>
  <year>2003</year>
  <price>39.95</price>
</book>

</bookstore>

And using this query:

copy $d := doc("books-mod.xml")
modify (
  for $t in $d//title
  return replace value of node $t with concat($t, " in bed")
)
return $d

This query runs and does what I expect (i.e. appends the text " in bed" to each book title). However, surprisingly, it also modifies the source document... I thought the whole point of copy with this transform was that we modify a copy of the document.

What am I missing here?

I'm using xqilla with -u to execute the query.

Leo Wörteler Leo Wörteler · Accepted Answer · 2012-04-17T19:54:38

You are right, this is definitely a bug. The Transform Expression is explicitly not an updating expression:

A transform expression is a simple expression because it does not modify the value of any existing nodes.

Which version of XQilla are you using? The change log for version 2.2.2 mentions something related:

Fixed the transform expression to copy document nodes rather than dissolving them.

So probably it's already fixed.

XQuery: why does this transform modify the source document?

1 Answers