XQuery Module

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This XQuery Module contains functions for evaluating XQuery strings and modules at runtime.

Contents

Conventions

All functions in this module are assigned to the http://basex.org/modules/xquery namespace, which is statically bound to the xquery prefix.
All errors are assigned to the http://basex.org/errors namespace, which is statically bound to the bxerr prefix.

Functions

xquery:eval

Signatures xquery:eval($query as xs:string) as item()*
xquery:eval($query as xs:string, $bindings as map(*)?) as item()*
xquery:eval($query as xs:string, $bindings as map(*)?, $options as map(xs:string, xs:string)) as item()*
Summary Evaluates the supplied $query string as XQuery expression and returns the resulting items.
The evaluated query has its own query context. If a returned node is stored in a database, a main-memory copy will be returned as result, because the referenced database is closed after query execution and will not be accessible anymore.
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 Clark Notation.
  • If the specified string is empty, the value will be bound to the context item.

The $options parameter contains evaluation options:

  • 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: set base-uri property for the query. This URI will be used when resolving relative URIs by functions such as fn:doc.
Errors BXXQ0001: the query contains updating expressions.
BXXQ0003: insufficient permissions for evaluating the query.
BXXQ0004: query execution exceeded timeout or memory limit.
BXXQ0005: nested query evaluation is not allowed.
Any other error that may occur while evaluating the query.
Examples
  • xquery:eval("1+3") returns 4.
  • You can bind the context and e.g. operate on a certain database only:
xquery:eval("//country", map { '': db:open('factbook') })
  • The following expressions use strings as keys. All of them return 'XML':
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' }
)
  • The following expressions use QNames as keys. All of them return 'XML':
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)

xquery:update

Signatures xquery:update($query as xs:string) as item()*
xquery:update($query as xs:string, $bindings as map(*)?) as item()*
xquery:update($query as xs:string, $bindings as map(*)?, $options as map(xs:string, xs:string)) as item()
Summary Evaluates $query as updating XQuery expression at runtime.
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 of the $bindings and $options parameters are the same as for xquery:eval.
Errors BXXQ0002: the query contains no updating expressions.
BXXQ0003: insufficient permissions for evaluating the query.
BXXQ0004: query execution exceeded timeout or memory limit.
BXXQ0005: nested query evaluation is not allowed.
Any other error that may occur while evaluating the query.

xquery:parse

Signatures xquery:parse($query as xs:string) as item()*
xquery:parse($query as xs:string, $options as map(*)) as item()
Summary Parses the specified $query string as XQuery module and returns the resulting query plan. The $options parameter influences the output:
  • compile: additionally compiles the query after parsing it. By default, this option is false.
  • plan: returns an XML representation of the internal query plan. By default, this option is true. The naming of the expressions in the query plan may change over time
  • pass: passes on the original error info (line and column number, optional file uri). By default, this option is false.
Errors Any error that may occur while parsing the query.
Examples
  • xquery:parse("1 + 3") returns:
<MainModule updating="false">
  <QueryPlan compiled="false">
    <Arith op="+">
      <Int value="1" type="xs:integer"/>
      <Int value="3" type="xs:integer"/>
    </Arith>
  </QueryPlan>
</MainModule>

xquery:parse-uri

Signatures xquery:parse-uri($uri as xs:string) as item()*
xquery:parse-uri($uri as xs:string, $options as map(*)) as item()*
Summary Parses the XQuery module located at $uri and returns the resulting query plan. A relative URI will be resolved against the static base URI of the query. The rules for the $options parameter are the same as for xquery:parse.
Errors Any error that may occur while parsing the query.

xquery:invoke

Signatures xquery:invoke($uri as xs:string) as item()*
xquery:invoke($uri as xs:string, $bindings as map(*)?) as item()*
xquery:invoke($uri as xs:string, $bindings as map(*)?, $options as map(*)) as item()*
Summary Evaluates the XQuery module located at $uri at runtime and returns the resulting items. A relative URI will be resolved against the static base URI of the query.
The rules of the $bindings and $options parameters are the same as for xquery:eval.
Errors BXXQ0001: the expression contains updating expressions.
BXXQ0003: insufficient permissions for evaluating the query.
BXXQ0004: query execution exceeded timeout.
BXXQ0005: nested query evaluation is not allowed.
Any other error that may occur while evaluating the query.

Parallelized Execution

Parallel query execution is recommendable if you have various calls that require a lot of time, but 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 can hardly be optimized by the caching strategies of HD, SSD or 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
  • The following function sleeps in parallel; it will be finished in 1 second if your system has at least 2 cores:
let $f := function() { prof:sleep(1000) }
return xquery:fork-join(($f, $f))
  • In the following query, up to four URLs will be requested in parallel:
let $funcs :=
  for $segment in 1 to 4
  let $url := 'http://url.com/path' || $segment
  return function() { http:send-request((), $url) }
return xquery:fork-join($funcs)
Errors BXXQ0006: an unexpected error occurred.

Errors

Code Description
BXXQ0001 The specified query contains updating expressions.
BXXQ0002 The specified query contains no updating expressions.
BXXQ0003 Insufficient permissions for evaluating the query.
BXXQ0004 Query execution exceeded timeout or memory limit.
BXXQ0005 Nested query evaluation is not allowed.
BXXQ0006 An unexpected error occurred.

Changelog

Version 8.5
Version 8.4
Version 8.0
Version 7.8.2
Version 7.8

This module was introduced with Version 7.3. Functions have been adopted from the obsolete Utility Module.

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