xpath from string

Question

I'm trying to do xpath expression from string literal. I create my xpath from some variables so I can't precalculate them. I end up with sth like this:

count(concat("//sales:", "$variable", "Available"))

and it results in an error:

Can not convert #STRING to a NodeList!

I think it would suffice if I could somehow evaluate() the result of concat so it would become the actual NodeList. Is there an appropriate function to do this?

I'm doing this text manipulation in Apache Camel, but it's not so important IMO.

EDITED:

To be more precise: Apache Camel works as a pipeline, XMLs go through it and you can process those XMLs in some ways - like impose some rules based on XMLs content or structure. That is why I need this to be dynamic.

My situation looks like this:

look at the xml and get the content of element operationName
search in some other document for an element that is constructed from the lower-cased operationName and string literal 'Available'

So if my operationName is FOOBAR, than I want to check for the existence of node //sales:foobarAvailable

You need dyn:evaluate, though it's poorly supported in implementations. — Flack
– Flack, Commented Feb 21, 2011 at 16:25
Dynamic evaluation inside an XPath expression? Shouldn't the host language do that composition before evaluation? — user357812
– user357812, Commented Feb 21, 2011 at 17:57

Dimitre Novatchev · Accepted Answer · 2011-02-21 20:52:15Z

2

Evaluation of dynamically generated XPath expressions is not supported in XSLT/XPath until version 3.0, which are in their early WD (working draft) status at present.

If more is known about the XPath expression, then usually some solution can be designed.

Therefore, if you describe your problem in more detail, the chances are good that someone would be able to help.

UPDATE: There is this new information from the OP:

So if my operationName is FOOBAR, than I want to check for the existence of node //sales:foobarAvailable

This is easy to do:

Use:

//sales:*[local-name()
         =
          concat(translate(operationName, $vUpper, $vLower), 'Available')
         ]

where $vUpper and $vLower are defined as (can be substituted by):

'ABCDEFGHIJKLMNOPQRSTUVWXYZ'

and

'abcdefghijklmnopqrstuvwxyz'

edited Feb 21, 2011 at 20:52

answered Feb 21, 2011 at 17:24

Dimitre Novatchev

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3 Comments

Marcin Cylke Over a year ago

Ok, I've added some more insight.

Dimitre Novatchev Over a year ago

@Marcin-Cylke: Yes, this can easily be achieved -- see the update of my answer.

Marcin Cylke Over a year ago

Your comment is great, it works perfectly - very clever way of doing this :)

Michael Kay · Accepted Answer · 2011-02-21 23:08:48Z

0

If your XSLT processor doesn't have an xx:evaluate extension (and you can't switch to one that does), then another technique that can be useful in some situations is to write a meta-stylesheet -- a stylesheet that creates or modifies another stylesheet. You then run these two in some kind of pipeline.

answered Feb 21, 2011 at 23:08

Michael Kay

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