Difference between revisions of "XQuery Module"
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=Changelog= | =Changelog= | ||
− | ;Version | + | ;Version 10 |
* Deleted: xquery:parse-uri (merged with [[#xquery:parse|xquery:parse]]) | * Deleted: xquery:parse-uri (merged with [[#xquery:parse|xquery:parse]]) |
Revision as of 09:42, 25 April 2022
This XQuery Module contains functions for parsing and evaluating XQuery strings at runtime, and to run code in parallel.
Contents
Conventions
All functions and errors in this module are assigned to the http://basex.org/modules/xquery
namespace, which is statically bound to the xquery
prefix.
Evaluation
xquery:eval
Signatures | xquery:eval($query as xs:anyAtomicType) as item()* xquery:eval($query as xs:anyAtomicType, $bindings as map(*)?) as item()* xquery:eval($query as xs:anyAtomicType, $bindings as map(*)?, $options as map(*)?) as item()* |
Summary | Evaluates the supplied $query and returns the resulting items. If the query is of type xs:anyURI , the module located at this URI will be retrieved (a relative URI will be resolved against the static base URI). Otherwise, the input is expected to be of type xs:string .
Variables and context items can be declared via
The
|
Errors | update : the query contains updating expressions.permission : insufficient permissions for evaluating the query.timeout : query execution exceeded timeout.limit : query execution exceeded memory limit.nested : nested query evaluation is not allowed.Any other error that may occur while evaluating the query. |
Examples |
<syntaxhighlight lang="xquery"> xquery:eval(xs:anyURI('cleanup.xq')) </syntaxhighlight>
<syntaxhighlight lang="xquery"> xquery:eval("//country", map { : db:open('factbook') }) </syntaxhighlight>
<syntaxhighlight lang="xquery"> xquery:eval(".", map { : 'XML' }), xquery:eval("declare variable $xml external; $xml", map { 'xml': 'XML' }), xquery:eval( "declare namespace pref='URI'; declare variable $pref:xml external; $pref:xml", map { '{URI}xml': 'XML' } ) </syntaxhighlight>
<syntaxhighlight lang="xquery"> declare namespace pref = 'URI'; xquery:eval("declare variable $xml external; $xml", map { xs:QName('xml'): 'XML' }), let $query := "declare namespace pref='URI'; declare variable $pref:xml external; $pref:xml" let $vars := map { xs:QName('pref:xml'): 'XML' } return xquery:eval($query, $vars) </syntaxhighlight> |
xquery:eval-update
Signatures | xquery:eval-update($query as xs:anyAtomicType) as item()* xquery:eval-update($query as xs:anyAtomicType, $bindings as map(*)?) as item()* xquery:eval-update($query as xs:anyAtomicType, $bindings as map(*)?, $options as map(*)?) as item()* |
Summary | Evaluates a query as updating expression. All updates will be added to the Pending Update List of the main query and performed after the evaluation of the main query. The rules for all arguments are the same as for xquery:eval. |
Errors | update : the query contains no updating expressions.permission : insufficient permissions for evaluating the query.timeout : query execution exceeded timeout.limit : query execution exceeded memory limit.nested : nested query evaluation is not allowed.Any other error that may occur while evaluating the query. |
Examples |
<syntaxhighlight lang="xquery"> xquery:eval-update(" delete node db:open('tmp')/*, update:output('TEMPORARY DATABASE WAS CLEANED UP') ") </syntaxhighlight> |
Parsing
xquery:parse
Template:Mark $query
can additionally be of type xs:anyURI
.
Signatures | xquery:parse($query as xs:anyAtomicType) as item()? xquery:parse($query as xs:anyAtomicType, $options as map(*)?) as item()? |
Summary | Parses the specified $query as XQuery module and returns the resulting query plan. If the query is of type xs:anyURI , the module located at this URI will be retrieved (a relative URI will be resolved against the static base URI). Otherwise, the input is expected to be of type xs:string . The $options parameter influences the output:
|
Errors | Any error that may occur while parsing the query. |
Examples |
<syntaxhighlight lang="xml"> <MainModule updating="false"> <QueryPlan compiled="false"> <Arith op="+"> <Int value="1" type="xs:integer"/> <Int value="3" type="xs:integer"/> </Arith> </QueryPlan> </MainModule> </syntaxhighlight> |
Parallelized Execution
Parallel query execution is recommendable if you have various calls that require a lot of time, but that cannot be sped up by rewriting the code. This is e. g. the case if external URLs are called. If you are parallelizing local data reads (such as the access to a database), single-threaded queries will usually be faster, because parallelized access to disk data often results in randomized access patterns, which will rarely be optimized by the caching strategies of HDDs, SSDs, or the operating system.
xquery:fork-join
Signatures | xquery:fork-join($functions as function(*)*) as item()*
|
Summary | This function executes the supplied (non-updating) functions in parallel. |
Examples |
<syntaxhighlight lang="xquery"> let $f := function() { prof:sleep(1000) } return xquery:fork-join(($f, $f)) </syntaxhighlight>
<syntaxhighlight lang="xquery"> xquery:fork-join( for $segment in 1 to 4 let $url := 'http://url.com/path/' || $segment return function() { http:send-request((), $url) } ) </syntaxhighlight> |
Errors | error : an unexpected error occurred.
|
Errors
Code | Description |
---|---|
permission
|
Insufficient permissions for evaluating the query. |
update
|
updating expression found or expected. |
timeout
|
Query execution exceeded timeout. |
memory
|
Query execution exceeded memory limit. |
nested
|
Nested query evaluation is not allowed. |
error
|
An unexpected error occurred. |
Changelog
- Version 10
- Deleted: xquery:parse-uri (merged with xquery:parse)
- Updated: xquery:parse: Template:$query can additionally be of type
xs:anyURI
.
- Version 9.2
- Deleted: xquery:invoke, xquery:invoke-update (merged with xquery:eval and xquery:eval-update)
- Version 9.0
- Added: xquery:invoke-update
- Updated: xquery:eval:
pass
option added - Updated: xquery:parse, xquery:parse-uri:
base-uri
option added - Updated: xquery:update renamed to xquery:eval-update
- Updated: error codes updated; errors now use the module namespace
- Version 8.5
- Added: xquery:fork-join
- Updated: xquery:eval:
base-uri
option added - Updated: Relative URIs will always be resolved against the static base URI of the query
- Deleted: xquery:type (moved to Profiling Module)
- Version 8.4
- Added: xquery:parse-uri
- Updated: xquery:parse:
pass
option added
- Version 8.0
- Added: xquery:update, xquery:parse
- Deleted: xquery:evaluate (opened databases will now be closed by main query)
- Version 7.8.2
- Added:
$options
argument
- Version 7.8
- Added: xquery:evaluate
- Updated: used variables must be explicitly declared in the query string.
This module was introduced with Version 7.3. Functions have been adopted from the obsolete Utility Module.