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XQuery Functions

This module contains functions for parsing and evaluating XQuery strings at runtime, and to run code in parallel.

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

Updated: The Clark notation was replaced with the Expanded QNames notation.

xquery:eval

Signature
xquery:eval(
  $query     as xs:anyAtomicType,
  $bindings  as map(*)?           := {},
  $options   as map(*)?           := {}
) as item()*
SummaryEvaluates 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 $bindings. The specified keys must be QNames or strings:

  • If a key is a QName, it will be directly adopted as variable name.
  • It a key is a string, it may be prefixed with a dollar sign. Namespace can be specified using the Expanded QNames notation.
  • If the specified string is empty, the value will be bound to the context item.

The following $options are available:

optiondefaultdescription
permission The query will be evaluated with the specified permissions (see User Management).
timeout Query execution will be interrupted after the specified number of seconds.
memory Query execution will be interrupted if the specified number of megabytes will be exceeded. This check works best if only one process is running at the same time. Moreover, please note that this option enforces garbage collection, so it will take some additional time, and it requires GC to be enabled in your JVM.
base-uri The base-uri property for the query. Overwrites the base URI of the query; will be used when resolving relative URIs by functions such as fn:doc.
passfalse() Pass on the original error info (line and column number, optional file URI).
Errors
limit
nestedNested query evaluation is not allowed.
permissionInsufficient permissions for evaluating the query.
timeoutQuery execution exceeded timeout.
updateupdating expression found or expected.
Examples
xquery:eval("1+3")
Result: 4
xquery:eval(xs:anyURI('cleanup.xq'))
If a URI is supplied, the query in the specified file will be evaluated.
xquery:eval("//country", { '': db:get('factbook') })
You can bind the context and e.g. operate on a certain database only.
xquery:eval(".", { '': 'XML' }),

xquery:eval(
  "declare variable $xml external; $xml",
  { 'xml': 'XML' }
),

xquery:eval(
  "declare namespace pref='URI';
   declare variable $pref:xml external;
   $pref:xml",
  { '{URI}xml': 'XML' }
)
The following expressions use strings as keys. All of them return XML.
declare namespace pref = 'URI';

xquery:eval(
  "declare variable $xml external; $xml",
  { xs:QName('xml'): 'XML' }
),

let $query := "declare namespace pref='URI';
               declare variable $pref:xml external;
               $pref:xml"
let $vars := { xs:QName('pref:xml'): 'XML' }
return xquery:eval($query, $vars)
The following expressions use QNames as keys. All of them return 'XML'.

xquery:eval-update

Signature
xquery:eval-update(
  $query     as xs:anyAtomicType,
  $bindings  as map(*)?           := (),
  $options   as map(*)?           := ()
) as item()*
SummaryEvaluates 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
limit
nestedNested query evaluation is not allowed.
permissionInsufficient permissions for evaluating the query.
timeoutQuery execution exceeded timeout.
updateupdating expression found or expected.
Examples
xquery:eval-update("
  delete node db:get('tmp')/*,
  update:output('TEMPORARY DATABASE WAS CLEANED UP')
")
Removes entries from a temporary databases and returns an info string.

Parsing

xquery:parse

Signature
xquery:parse(
  $query    as xs:anyAtomicType,
  $options  as map(*)?           := {}
) as item()?
SummaryParses 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 following $options are available:
optiondefaultdescription
compilefalse() Additionally compile the query after parsing it.
plantrue() Return an XML representation of the internal query plan. Note that the naming of the expressions in the query plan may change over time.
passfalse() If an error is raised, the line/column number and the optional file uri will refer to the location of the function call. If the option is enabled, the line/column and file uri will be adopted from the raised error.
base-uri The base-uri property for the query. This URI will be used when resolving relative URIs by functions such as fn:doc.
Examples
xquery:parse("1 + 3")
The result:
<MainModule updating="false">
  <QueryPlan compiled="false" updating="false">
    <Arith op="+" type="xs:anyAtomicType?">
      <Int type="xs:integer" size="1">1</Int>
      <Int type="xs:integer" size="1">3</Int>
    </Arith>
  </QueryPlan>
</MainModule>

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

Updated: Options added.

Signature
xquery:fork-join(
  $functions  as fn(*)*,
  $options    as map(*)?  := {}
) as item()*
SummaryThis function executes the supplied (non-updating) $functions in parallel. The following $options are available:
optiondefaultdescription
parallel Maximum number of parallel threads. If the value is smaller than 1, or if the option is omitted, the number of available processors is used.
resulttrue() Suppress or return the function results.
errorstrue() Ignore or raise errors.
Errors
errorAn unexpected error occurred.
Examples
xquery:fork-join(
  for $segment in 1 to 100
  let $url := 'http://url.com/path/' || $segment
  return fn() { http:send-request((), $url) },
  { 'parallel': 8 }
)
Requests 100 URLs, use at most 8 parallel threads.
let $f := fn() { prof:sleep(1000) }
return xquery:fork-join(($f, $f))
Parallel sleep function calls. The function is expected to finish in 1 second if the system has at least 2 cores.

Errors

CodeDescription
errorAn unexpected error occurred.
memoryQuery execution exceeded memory limit.
nestedNested query evaluation is not allowed.
permissionInsufficient permissions for evaluating the query.
timeoutQuery execution exceeded timeout.
updateupdating expression found or expected.

Changelog

Version 11Version 10
  • Updated: xquery:parse: $query can additionally be of type xs:anyURI.
  • Deleted: xquery:parse-uri (merged with xquery:parse)
Version 9.2Version 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 8.5Version 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.
Version 7.3
  • Added: New module added. Functions have been adopted from the obsolete Utility Module.

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