I'm maintaining a legacy tool of the company I work for written in C# and I'm converting it to .Net standard 2.0. It uses the Saxon-HE processor to process some XPaths and replace some configurations in files.
Its NuGet package on .NET has dependencies that do not allow the execution on all the .Net standard 2.0 compliant platforms (in my case both .Net Framework and .Net core), so I need to replace it with one another tool, better if the standard .Net XPath library.
The problem is that the tool uses some XPaths that perform complex operations such as concatenate strings and select an array item, and I don't know if it's a Saxon-specific syntax or regards a standard.
It is important to know this because if the XPaths are compliant to some XPath standard I could find one another way to process the same XPaths.
Here is some examples:
First:
for $row in /Item/SubItem[*]/SubSubItem return(concat($row, \"/ConcatValue\"))
Second:
/Item/SubItem[*]/SubSubItem/(add[#key=\"TheKey\"]/#value/string(), '')[1]
Do you know something about this XPath syntax?
Thank you
The XPath expressions you have given as examples require an XPath 2.0 processor but they are not specific to Saxon.
The expression
for $row in /Item/SubItem[*]/SubSubItem return(concat($row, \"/ConcatValue\"))
is a ForExpression, which is specific to XPath 2.0, and is not easily converted to XPath 1.0 because its result is a sequence of strings, and there is no such data type in XPath 1.0.
The expression
/Item/SubItem[*]/SubSubItem/(add[#key=\"TheKey\"]/#value/string(), '')[1]
is specific to XPath 2.0 because it uses a parenthesized expression on the RHS of the "/" operator; and again, because it returns a sequence of strings.
I'm afraid I can't advise you whether there exist XPath 2.0 libraries that run on .NET Core, which I assume is your requirement. Saxon cannot be made to run on .NET Core because of its dependency on IKVM, which doesn't support that platform and which (I gather) cannot readily be adapted to do so.
Note that XPath 2.0 is a subset of XQuery 1.0, so you could extend your search to XQuery 1.0 processors as well as XPath 2.0 processors.
Thanks to this comment I was able to test XPath2.Net and now everything works. I needed to change only one type of XPath definition
This one:
/Item/SubItem[*]/SubSubItem/(add[#key=\"TheKey\"]/#value/string(), '')[1]
Changes to
/Item/SubItem[*]/SubSubItem/(add[#key=\"TheKey\"]/#value/string(.), '')[1]
Please note the additional dot argument of the string() function.
This is strange as it should not be require the dot; in fact, per standard
In the zero-argument version of the function, $arg defaults to the
context item. That is, calling fn:string() is equivalent to calling
fn:string(.)
but XPath2 complains with this error
{"The function 'string'/0 was not found in namespace 'http://www.w3.org/2003/11/xpath-functions'"}
UPDATE:
After updating the XPath2.Net library to version 1.0.8 the string() syntax works.
Related
When I evaluate this XPath expression: //superhero[n0:name="Superman"]/n1:name on this xml:
<n0:rootElement xmlns:n0='http://example.com' xmlns:n1='http://example.com'>
<superheroes>
<superhero>
<n0:name>Superman</n0:name>
<n1:name>Clark</n1:name>
</superhero>
<superhero>
<n0:name>Spiderman</n0:name>
<n1:name>Peter</n1:name>
</superhero>
</superheroes>
</n0:rootElement>
using an XPath evaluator, I get the expected result.
But when I send it to an XQuery processor, I get an error message saying that
Namespace prefix 'n0' has not been declared. Weird, huh?
It's always the prefix in the brackets (is it called a filter, maybe?) that gets the complaint.
I've used http://www.xpathtester.com to verify the difference between XPath and XQuery interpretations.
It works fine with https://codebeautify.org/Xpath-Tester which is XPath only.
If I replace n0: or n1: with *: it works in for XQuery processors, but not for XPath testers.
This is of course a toy example I've written up to clarify my issue. In production I'm calling an external service which I believe is driven by Saxon-HE. I know it accepts XQuery so I'm guessing it is in "XQuery-mode" for XPath expressions.
There isn't much I can do to the xml file since I receive it from another source. Is there a better XQuery expression I can use?
Is this a bug, or by design?
Different XPath engines provide different ways of binding the namespace prefixes used in the expression. Some, I believe, pick up the namespace bindings from the source document. So it's not a non-conformance with the standard, it's the fact that the standard leaves it up to the particular processor how the original context is established.
The underlying problem is that you probably want your query to work regardless what namespace prefixes are used in the source document. Picking up the namespace bindings from the source document is handy for ad-hoc queries, but it means that a query that does the right thing with one document will fail with a different one.
In XQuery you can declare any namespaces you want to use in your query:
declare namespace n0 = 'http://example.com';
declare namespace n1 = 'http://example.com';
//superhero[n0:name="Superman"]/n1:name
https://xqueryfiddle.liberty-development.net/bdxZ8S
See the spec at https://www.w3.org/TR/xquery-31/#id-namespace-declaration
We are using Saxon, calling it from Java, to perform queries. When we upgrade to XPath 3.1, will it handle all queries written for XPath 2.0 the same as before? Or are there changes in what is returned for some queries?
I'm asking because if it's 100% upwardly compatible, we just change our existing XPath 2.0 code to use XPath 3.1. But if it's different, then we need to add XPath 3.1 as a new datasource type.
We do have XPath 1.0 as a distinct datasource because there are differences between what XPath 1.0 and 2.0 return for some queries.
You can assure this premise by following this chain:
XPath-3.0 is backwards compatible to XPath-2.0
This appendix provides a summary of the areas of incompatibility between XPath 3.0 and [XML Path Language (XPath) Version 1.0]. In each of these cases, an XPath 3.0 processor is compatible with an XPath 2.0 processor.
XPath-3.1 is backwards compatible to XPath-3.0.
This Recommendation specifies XPath version 3.1, a fully compatible extension of XPath version 3.0.
XPath 3.1 allows new expressions for arrays, maps and functions so if you have a test suite checking for some syntax errors in XPath 2 expressions you might find they could be allowed in XPath 3.1 and don't give an error.
The main error I remember to be converted into legal syntax is foo/[bar] which constructs an array in XPath 3.1 in the last step.
I need to get the values from a DOM object using Java, I would like to know the differences between XPath & JXPath.
XPath is a W3C-defined language for finding data within XML documents. There are many implementations. The latest version is XPath 3.1, but many implementations only support the original version 1.0.
JXPath is an open-source library that implements (some version of?) the XPath language, applying it specifically to navigation of an XML view of a general graph of Java objects, rather than an XML document per se.
I have found that Saxon implementation of XPath 2.0 supports both 'instance of' and 'castable as' as valid ways of obtaining the type of a value, as explained in this website.
This seems to be a Saxon specific syntax. Does a standard way of obtaining the type of a node exist?
XPath 2.0 is a W3C recommendation that Saxon implements and the operators instance of and castable as a part of that standard, see https://www.w3.org/TR/xpath20/#id-instance-of and https://www.w3.org/TR/xpath20/#id-castable.
Currently, I'm writing something to do Unit testing for XSLT2 functions, the idea is very simple:
Create a custom-library.xsl, which contains some custom XSLT2 functions.
Create a data XML contains the test cases, as following XML Schema xslunit.xsd:
schema structure http://xml.bodz.net/schema/xslunit/xslunit.png
Run the test cases by transform it, using xslunit-xslt2.xsl, and get the test result html.
Now, the question is, there is function-call in the test cases, and I have to evaluate it in the XSLT (file xslunit-xslt2.xsl). But I can't find a way to evaluate an XPath.
Though, it may be easy to using some kind of Java extensions, but I really don't want to bring in another trouble. I hope everything can just work with-in XSLT2 only.
No, pure XSLT 2.0 does not have support do evaluate an XPath expression found in your XML data. Saxon 9 (in its commercial editions) however has an extension function: http://www.saxonica.com/documentation/extensions/functions/evaluate.xml. And AltovaXML Tools has a similar one: http://manual.altova.com/AltovaXML/altovaxmlcommunity/index.html?xextaltova_general.htm
Update a decade later: XSLT 3.0 has an instruction <xsl:evaluate> which evaluates an XPath expression supplied dynamically as a string.