Constructing, not selecting, XSL node set variable

问题

I wish to construct an XSL node set variable using a contained for-each loop. It is important that the constructed node set is the original (a selected) node set, not a copy.

Here is a much simplified version of my problem (which could of course be solved with a select, but that's not the point of the question). I've used the <name> node to test that the constructed node set variable is in fact in the original tree and not a copy.

XSL version 1.0, processor is msxsl.

Non-working XSL:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="text" encoding="iso-8859-1" omit-xml-declaration="yes" />

<xsl:template match="/">

    <xsl:variable name="entries">
        <xsl:for-each select="//entry">
            <xsl:copy-of select="."/>
        </xsl:for-each>
    </xsl:variable>

    <xsl:variable name="entryNodes" select="msxsl:node-set($entries)"/>

    <xsl:for-each select="$entryNodes">
        <xsl:value-of select="/root/name"/>
        <xsl:value-of select="."/>
    </xsl:for-each>

</xsl:template>

</xsl:stylesheet>

XML input:

<?xml version="1.0" encoding="UTF-8"?>
<root>
    <name>X</name>
    <entry>1</entry>
    <entry>2</entry>
</root>

Wanted output:

X1X2

Actual output:

12

Of course the (or a) problem is the copy-of, but I can't work out a way around this.

回答1:

There isn't a "way around it" in XSLT 1.0 - it's exactly how this is supposed to work. When you have a variable that is declared with content rather than with a select then that content is a result tree fragment consisting of newly-created nodes (even if those nodes are a copy of nodes from the original tree). If you want to refer to the original nodes attached to the original tree then you must declare the variable using select. A better question would be to detail the actual problem and ask how you could write a suitable select expression to find the nodes you want without needing to use for-each - most uses of xsl:if or xsl:choose can be replaced with suitably constructed predicates, maybe involving judicious use of xsl:key, etc.

---

In XSLT 2.0 it's much more flexible. There's no distinction between node sets and result tree fragments, and the content of an xsl:variable is treated as a generic "sequence constructor" which can give you new nodes if you construct or copy them:

<xsl:variable name="example" as="node()*">
  <xsl:copy-of select="//entry" />
</xsl:variable>

or the original nodes if you use xsl:sequence:

<xsl:variable name="example" as="node()*">
  <xsl:sequence select="//entry" />
</xsl:variable>

回答2:

I wish to construct an XSL node set variable using a contained for-each loop.

I have no idea what that means.

It is important that the constructed node set is the original (a selected) node set, not a copy.

This part I think I understand a little better. It seems you need to replace:

<xsl:variable name="entries">
    <xsl:for-each select="//entry">
        <xsl:copy-of select="."/>
    </xsl:for-each>
</xsl:variable>

with:

<xsl:variable name="entries" select="//entry"/>

or, preferably:

<xsl:variable name="entries" select="root/entry"/>

The resulting variable is a node-set of the original entry nodes, so you can do simply:

<xsl:for-each select="$entries">
    <xsl:value-of select="/root/name"/>
    <xsl:value-of select="."/>
</xsl:for-each>

to get your expected result.

Of course, you could do the same thing by operating directly on the original nodes, in their original context - without requiring the variable.

---

In response to the comments you've made:

We obviously need a better example here, but I think I am getting a vague idea of where you want to go with this. But there are a few things you must understand first:

1.
In order to construct a variable which contains a node-set of nodes in their original context, you must use select. This does not place any limits whatsoever on what you can select. You can do your selection all at once, or in stages, or even in a loop (here I mean a real loop). You can combine the intermediate selections you have made in any way sets can be combined: union, intersection, or difference. But you must use select in all these steps, otherwise you will end up with a set of new nodes, no longer having the context they did in the source tree.

IOW, the only difference between using copy and select is that the former creates new nodes, which is precisely what you wish to avoid.

2.
xsl:for-each is not a loop. It has no hierarchy or chronology. All the nodes are processed in parallel, and there is no way to use the result of previous iteration in the current one - because no iteration is "previous" to another.

If you try to use xsl:for-each in order to add each of n processed nodes to a pre-existing node-set, you will end up with n results, each containing the pre-existing node-set joined with one of the processed nodes.

3.
I think you'll find the XPath language is quite powerful, and allows you to select the nodes you want without having to go through the complicated loops you hint at.

回答3:

It might help if you showed us a problem that can't be trivially solved in XSLT 1.0. You can't solve your problem the way you are asking for: there is no equivalent of xsl:sequence in XSLT 1.0. But the problem you have shown us can be solved without such a construct. So please explain why you need what you are asking for.

来源：https://stackoverflow.com/questions/28631847/constructing-not-selecting-xsl-node-set-variable