XPath - context node evaluation problem

Thomas Schmidt · Jan 9, 2007

Given this document:

<doc>
<head>
<someElementWithID id="X"/>
<someElementWithID id="Y"/>
</head>
<body>
<element>
<otherElement>
<elementWithIDREF idref="X"/>
</otherElement>
</element>
</body>
</doc>

With the <elementWithIDREF> as a context node, I want to use an XPath
to get to the <someElementWithID> with the corresponding id-attribute.
If I use

//head/someElementWithID[@id=@idref]

I don't get what I want, because the idref-attribute is evaluated with
someElementWithID as the context. In XSLT, I use

//head/someElementWithID[@id=current()/@idref]

But "current()" is an XSLT function. Is there some way to do this in
"pure" XPath?

Any help will be greatly appreciated,

Thomas

Philippe Poulard · Jan 9, 2007

hi,

Thomas said:
//head/someElementWithID[@id=current()/@idref]

But "current()" is an XSLT function. Is there some way to do this in
"pure" XPath?

The XPath context consist on a node, a pair of integer (size and
position), a set of namespace bindings, a set of functions, and a set of
variables

If you dont' want to augment the set of functions, you can use a
variable instead :

//head/someElementWithID[@id=$current/@idref]

but you have to set $current before, that depends on the XPath engine
and the host language you use

--
Cordialement,

///
(. .)
--------ooO--(_)--Ooo--------
| Philippe Poulard |
-----------------------------
http://reflex.gforge.inria.fr/
Have the RefleX !

Bjoern Hoehrmann · Jan 9, 2007

* Thomas Schmidt wrote in comp.text.xml:

I don't get what I want, because the idref-attribute is evaluated with
someElementWithID as the context. In XSLT, I use

//head/someElementWithID[@id=current()/@idref]

But "current()" is an XSLT function. Is there some way to do this in
"pure" XPath?

Well, can you use the id() function, or variables, or insert the value
into the expression before you have it evaluated? Otherwise there is no
way, you could only check whether there is some such element using

//head/someElementWithID/@id = @idref

which is not what you want.

Dimitre Novatchev · Jan 9, 2007

If you can uniquely select the element with the "idref" attribute" then use
the following expression:

//someElementWithID[@id=$the-id-ref-elemennt-selecting-expression-here/@ideref]

for example, for the provided xml document this could be as simple as:

//someElementWithID[@id = /*/*/*/elementWithIDREF/@idref]

Cheers,
Dimitre Novatchev

David Carlisle · Jan 10, 2007

Thomas said:
With the <elementWithIDREF> as a context node, I want to use an XPath
to get to the <someElementWithID> with the corresponding id-attribute.
If I use

//head/someElementWithID[@id=@idref]

I don't get what I want, because the idref-attribute is evaluated with
someElementWithID as the context. In XSLT, I use

//head/someElementWithID[@id=current()/@idref]

But "current()" is an XSLT function. Is there some way to do this in
"pure" XPath?

Any help will be greatly appreciated,

Thomas

(in xslt its usually better to use a key rather than
/head/someElementWithID[@id=current()/@idref] not that that's relevant
to the problem here)

i suspect it's not possible in xpath1 unless you bind a variable in an
external language. or as Dimitre suggested, know a path to your
referencing node.

if xpath2 is a possibility, then you could use

for $id in @idref return
//head/someElementWithID[@id=$id]

David

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XPath - context node evaluation problem

Thomas Schmidt

Philippe Poulard

Bjoern Hoehrmann

Dimitre Novatchev

David Carlisle

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