I too have had a go at this, but I too am not an XPath expert.
First of all make sure you have _all of_ saxon8.jar and
saxon8-dom.jar
and xbean_xpath.jar (in addition to the normal xbean.jar and the JSR
173
jar) on your classpath. Not having saxon8-dom.jar can cause strange
errors. Not having xbean_xpath.jar just means that no XPath will work.
Other than that I think it might just be that we're not passing in
the
right XPath. Siegfried, can you attach an example XML instance
document
for which you are expecting this to work?
Here's the one I tried:
<elem1 xmlns=\"http://laj.org/test\"; >
<elem11 id=\"123\" >text11</elem11>
<elem21 id=\"456\" >text11</elem21>
<elem12 idRef=\"123\" />
<elem13 idRef=\"456\" />
<elem14 idRef=\"123\" />
<elem15 idRef=\"456\" />
<elem16 idRef=\"123\" />
<elem17 idRef=\"789\" />
</elem1>
And here are the issues I see.
1. The element on which you perform the selectPath() call seems to
represent the root as far as the call to selectPath() is concerned.
So
if e.g. you passed in only the XmlObject for <elem11> above you
should
not expect any of the other elements to be returned regardless of
the
XPath passed in.
2. But it is likely that the elements with idRef in them are _not_
children of the element with id in them. Rather it is likely that
they
are all members of some larger document element such as <elem1>
above.
So to get the selectPath() to even consider them you would need to
pass
in the XmlObject for <elem1> (or at least some element that is a
root to
all of the results you expect).
3. But then the path to the id attribute is no longer $this/@id as
that
would only match the _root_ element (<elem1> in this case) having an
id
attribute. Exactly what you need to pass in depends on what you
want to
do - if you want to find all idRefs that match _any_ id attribute
anywhere in the document then you probably want $this//@id instead.
4. I tried the XPath //[EMAIL PROTECTED]//@id] on the complete document
above (i.e. I executed selectPath() on the XmlObject representing
<elem1>) and printed out the list of XmlObjects returned from
selectPath(). I got:
Number of results = 5
results[0] = <xml-fragment idRef="123"/>
results[1] = <xml-fragment idRef="456"/>
results[2] = <xml-fragment idRef="123"/>
results[3] = <xml-fragment idRef="456"/>
results[4] = <xml-fragment idRef="123"/>
which is what I'd expect i.e. I get all the nodes with an idRef
that
matches any id attribute somewhere else in the document (and I don't
get
those that do not match). Not sure why they are xml-fragment's rather
than proper individual elements with proper QNames but that's a
different issue.
5. Note that replacing '$this' with '.' (i.e. XPath = //[EMAIL
PROTECTED]//@id)
gave me an empty result set. My guess is that '.' is evaluated
dynamically (i.e. it means the current node that the query has
evaluated
to) compared to $this which is bound statically at the beginning to
the
root node that you pass in. (With the '.' version of the XPath I
think
you are looking for a node which has both an id and an idRef
attribute
where the values are the same - which is a slightly different
query.)
I haven't tried this exhaustively - I'm not sure what would happen
if
some of the id or idRef attributes were on elements at deeper
levels.
But anyway I hope that helps get started.
Cheers,
Lawrence
-----Original Message-----
From: Radu Preotiuc-Pietro
Sent: Thursday, March 30, 2006 1:56 PM
To: user@xmlbeans.apache.org
Subject: RE: selectPath with FilterExpression using $this
I was curious to try this myself with the new Saxon 8.6 integration
(available from the SVN head only, for the moment) and what I found
is
that the path you are suggesting ("//[EMAIL PROTECTED]/@id]") works (no
exception) but for some reason doesn't return anything. On the other
hand, "//[EMAIL PROTECTED]'1'" returns the expected result, so on one
hand I
am
wondering if this is maybe a bug in the free version of Saxon and
on
the
other you can use this to workaround the problem by doing
.selectPath("//[EMAIL PROTECTED]'" + node.getId() + "'").
If anyone else has other insights into why the original path does
not
work (with more Xpath/Saxon knowledge), I'd also be interested to
know.
Thanks,
Radu
-----Original Message-----
From: Cezar Andrei
Sent: Wednesday, March 29, 2006 3:30 PM
To: user@xmlbeans.apache.org
Subject: RE: selectPath with FilterExpression using $this
Hi Siegfried,
I'm not an expert in xpath/xquery but I'm pretty sure that $this
doesn't
represent the internal current node that is processed by the engine.
So you'll probably want to rewrite the expression to something like
this:
xo.selectPath(".//[EMAIL PROTECTED]//@id]");
As for $this, it's just a variable that is bound to the XmlObject
that
you are calling the selectPath method from. The '$this' construction
is
not in the latest XPath/Xquery spec so it was deprecated, instead "."
should be used.
The current XmlObject can be bound to any user specified variable
name
as in the following example:
XmlOptions options = new XmlOptions();
options.setXqueryCurrentNodeVar("myVariable");
XmlObject[] res = xo.selectPath("declare variable $myVariable
external; $myVariable//el1", options);
Which is equivalent to:
XmlObject[] res = xo.selectPath(".//el1", options);
And to the following (since in the context of the xpath engine the
xo
is
considered the root):
XmlObject[] res = xo.selectPath("//el1", options);
Since we don't control Saxon, we can't promise that expressions
confirming to the spec will work. We can only work on making sure
we
make the right calls into Saxon.
Cezar
-----Original Message-----
From: Siegfried Baiz [mailto:[EMAIL PROTECTED]
Sent: Tuesday, March 14, 2006 12:11 PM
To: user@xmlbeans.apache.org
Subject: selectPath with FilterExpression using $this
Hello,
for a given XmlObject xo with an ID-Attribute 'id', I've tried to
launch the following xpath-expression:
xo.selectPath("//[EMAIL PROTECTED]/@id]")
in order to get all nodes (with idRef-Attribute) refering to my node
xo.
Unfortunatlly this expression seems not to work. I always get an
java.lang.ArrayIndexOutOfBoundsException from the underlying
net.sf.saxon.expr.XPathContextMajor.setLocalVariable(XPathContextMajor.j
av
a:213)
At
http://xmlbeans.apache.org/docs/2.0.0/guide/conSelectingXMLwithXQueryPat
hX
Path.html
I found the following notice:
"Notice in the query expression that the variable $this
represents
the current context node (the XmlObject that you are querying
from).
In this example you are querying from the document level
XmlObject."
After reading that sentence I've been thinking, that $this is
somehow
similar to "curent()" in XSLT, but maybe a got the meaning wrong.
Does anyone know whats the problem here rsp.
is there a better way to accomplish the same thing?
Thanks a lot,
Siggi
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