From your example it seemed that the util:eval() built-in extension of eXist was enough for the XPath evaluation that you needed. Other option is to split the query in two steps: the first step is an XQuery that evaluates the part of the XPath expression that is passed as parameter in your example and the second step is an XQuery applied to the result of the first step to do the main task of your query. Regards, Sorin Paul Ryan wrote:
Ok, that being the case it sound like my only option is to make my own extension of eXist. I'll go down that path (unless I'm misunderstanding).
Thanks,
-- Paul Ryan
-----Original Message----- From: oxygen-user-bounces@oxygenxml.com [mailto:oxygen-user-bounces@oxygenxml.com] On Behalf Of Sorin Ristache Sent: Monday, January 19, 2009 2:24 AM To: oxygen-user@oxygenxml.com Subject: Re: [oXygen-user] Preprocessing Xquery
Hello,
No, the validation scenario does not help you to insert your pre-processing step before sending the XQuery file to the eXist database. The database always receives the file content that is displayed in the Oxygen editor panel. You can use a scenario only for setting eXist as the validating engine instead of the default one (Saxon 9) so that the validation action does not report the eXist extension as an error and I suggested that before understanding what you mean by queries not supported "as is".
The validation scenario is explained in the User Manual:
http://www.oxygenxml.com/doc/ug-oxygen/validation-scenario.html
Regards, Sorin
Paul Ryan wrote:
Sorrin,
I understand the delima you present and we've put sufficient limitations on preprocessor to ensure proper context. In your first email you stated that I would override the validation scenario such as is done by exist. Is there a special API I should follow or just the standard xmldb-api from 2002 should do?
Thanks,
-- Paul Ryan
-----Original Message----- From: oxygen-user-bounces@oxygenxml.com [mailto:oxygen-user-bounces@oxygenxml.com] On Behalf Of Sorin Ristache Sent: Wednesday, January 14, 2009 8:24 AM To: oxygen-user@oxygenxml.com Subject: Re: [oXygen-user] Preprocessing Xquery
Hello,
If you need to compose an XPath expression with the runtime value of a parameter of the query then you need what is called a dynamic evaluation of an XPath expression. The standard XQuery language does not provide such an evaluation which seems to be due (some experts say that) to the difficulty of determining the evaluation context. That means you should use an extension function implemented in the specific XQuery engine that runs your queries, for example util:eval() in eXist or saxon:evaluate() in Saxon 9 instead of implementing your own mechanism of dynamic evaluation (your token pre-processor) and this is why Oxygen does not provide such a mechanism.
The eXist extension function is explained at:
Regards, Sorin
Paul Ryan wrote:
What you suggest poses a unique problem however because the java would have to know ahead of time (prior to calling xquery) if the string being passed will be used in an evaluation. This limitation with external variables of having to pre-evaluate passed elements is a large hole for us. The middle tier that is passing the query arguments doesn't know what variables will be used for evaluation however the XQuery string/document has this information. To ensure that string variables that need to be evaluated can be evaluated we opted to create a token preprocessor vs. building logic into the java to predetermine if it should evaluate the variable to an element.
As an example parsing the following has this issue:
Exist xquery - xquery version "1.0";
import module namespace util="http://exist-db.org/xquery/util"; declare variable $path as xs:string external;
let $query := concat('for $x in collection()',$path, ' return $x') return util:eval($query)
Desired xquery - xquery version "1.0";
declare variable $path as xs:string external;
for $x in collection()$path return $x
Token syntax for achieving desired xquery- xquery version "1.0";
for $x in collection()${path} return $x
Result of preprocessing on tokens- xquery version "1.0";
for $x in collection()/mypath[@id='myid'] return $x
Our preprocessor handles a little more than is shown but the example above is the general idea behind our preprocessor.
-- Paul Ryan
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