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This [[Module Library|XQuery Module]] contains functions to access remote BaseX server instances from XQuery. With this module, you can on the one hand execute database commands and on evaluate XQuery expressions. Please note that the other hand client module should always be used to address independent BaseX server instances. You can create deadlocks if you evaluate queriesa query with a server instance, and if you are addressing the results of which are returned as XDM sequencessame server instance in your query. See the following example: <syntaxhighlight lang="xquery">(: Retrieve documents from database :)let $client-id := client:connect('localhost', 1984, 'admin', '...')let $docs := client:query($client-id, 'db:get("conflict")')(: Create database with same name :)return db:create('conflict', $docs, $docs ! db:path(.)) </syntaxhighlight> The read-only query cannot be processed, because the <code>conflict</code> database is currently write-locked by the main query. See [[Transaction Management]] for more background information.
=Conventions=
All functions and errors in this module are assigned to the {{Code|<code><nowiki>http://basex.org/modules/client}} </nowiki></code> namespace, which is statically bound to the {{Code|client}} prefix.<br/>All errors are assigned to the {{Code|http://basex.org/errors}} namespace, which is statically bound to the {{Code|bxerr}} prefix.
=Functions=
==client:connect==
 
{| width='100%'
|-valign="top"
| width='120' | '''Signatures'''
|{{Func|client:connect|$host as xs:string, $port as xs:integer, $user username as xs:string, $password as xs:string|xs:anyURI}}<br/ >|-valign="top"
|'''Summary'''
|This function establishes a connection to a remote BaseX server, creates a new client session, and returns a session id. The parameter {{Code|$host}} is the name of the database server, {{Code|$port}} specifies the server port, and {{Code|$userusername}} and {{Code|$password}} represent the login data.|-valign="top"
|'''Errors'''
|{{Error|BXCL0001connect|#Errors}} an error occurs while creating the session (possible reasons: server not available, access denied).<br/>
|}
==client:execute==
 
{| width='100%'
|-valign="top"
| width='120' | '''Signatures'''
|{{Func|client:execute|$id as xs:anyURI, $command as xs:string|xs:string}}
|-valign="top"
| '''Summary'''
| This function executes a [[Commands|command]] and returns the result as a string. The parameter {{Code|$id}} contains the session id ID returned by [[Client Module#client:connect{{Function||client:connect]]}}. The {{Code|$command}} argument represents a single command, which will be executed by the server.|-valign="top"
|'''Errors'''
|{{Error|BXCL0003error|#Errors}} an I/O error occurs while transferring data from or to the server.<br/>{{Error|BXCL0004command|#Errors}} an error occurs while executing a command.|-valign="top"
| '''Examples'''
|The following query creates a new database {{Code|TEST}} on a remote BaseX server:
<pre classsyntaxhighlight lang="brush:xquery">client:connect('basex.server.org', 8080, 'admin', 'admin...') !
client:execute(., 'create database TEST')
</presyntaxhighlight>
|}
{| width='100%'
|-valign="top"
| width='120' | '''Signatures'''
|{{Func|client:info|$id as xs:anyURI|xs:string}}
|-valign="top"
| '''Summary'''
| This function returns an information string, created by a previous the last call of [[#client:execute{{Function||client:execute]]}}. {{Code|$id}} specifies the session id.
|}
==client:query==
 
{{Version|8.0}}: Values with more than one item can now be specified.
{| width='100%'
|-valign="top"
| width='120' | '''Signatures'''
|{{Func|client:query|$id as xs:anyURI, $query as xs:string|item()*}}<br/>{{Func|client:query|$id as xs:anyURI, $query as xs:string, $bindings as map(*)?|item()*}}|-valign="top"
| '''Summary'''
|Evaluates a query and returns the result as sequence. The parameter {{Code|$id}} contains the session id returned by [[Client Module#client:connect{{Function||client:connect]]}}, and {{Code|$query}} represents the query string, which will be evaluated by the server.<br />Variables and the context item can be declared via {{Code|$bindings}}. The specified keys must be QNames or strings:
* If a key is a QName, it will be directly adopted as variable name.
* If a key is a string, it may be prefixed with a dollar sign. A namespace can be specified using the [http://www.jclark.com/xml/xmlns.htm Clark Notation]. If the specified string is empty, the value will be bound to the context item.
|-valign="top"
|'''Errors'''
|{{Error|BXCL0003error|#Errors}} an I/O error occurs while transferring data from or to the server.<br/>{{Error|BXCL0005query|#Errors}} an error occurs while evaluating a query, and if the original error cannot be extracted from the returned error string.<br/>{{Error|BXCL0006function|#Errors}} a value to function items (including maps and arrays) cannot be bound is no single itemreturned.|-valign="top"
| '''Examples'''
|The following query sends a query on a local server instance, binds the integer {{Code|123}} to the variable {{Code|$n}} and returns {{Code|246}}:
<pre classsyntaxhighlight lang="brush:xquery">let $c := client:connect('localhost', 1984, 'admin', 'admin...')return client:query($c, "declare variable $n external; $n * 2", map{ 'n': 123 })</presyntaxhighlight>
The following query performs a query on a first server, the results of which are passed on to a second server:
<pre classsyntaxhighlight lang="brush:xquery">
let $c1 := client:connect('basex1.server.org', 8080, 'jack', 'C0S19tt2X')
let $c2 := client:connect('basex2.server.org', 8080, 'john', '465wFHe26')
for $it in client:query($c1, '1 to 10')
return client:query($c2, $it || '* 2')
</presyntaxhighlight>
|}
==client:close==
 
{| width='100%'
|-valign="top"
| width='120' | '''Signatures'''
|{{Func|client:close|$id as xs:anyURI|empty-sequence()}}
|-valign="top"
| '''Summary'''
| This function closes a client session. {{Code|$id}} specifies the session id.<br/>At Opened connections will automatically be closed after the end of query executionXQuery expression has been evaluated, but it is recommendable to explicitly close them with this function if you open sessions will be automatically closedmany connections.|-valign="top"
|'''Errors'''
|{{Error|BXCL0003error|#Errors}} an I/O error occurs while transferring data from or to the server.
|}
! width="110"|Code
|Description
|-valign="top"|{{Code|BXCL0001command}}| An error occurred while executing a command.|- valign="top"|{{Code|connect}}
| An error occurred while creating a new session (possible reasons: server not available, access denied).
|-valign="top"|{{Code|BXCL0002}}| The specified session is unknown, or has already been closed.|-|{{Code|BXCL0003error}}
| An I/O error occurred while transferring data from or to the server.
|-valign="top"|{{Code|BXCL0004function}}| An error occurred while executing a commandFunction items (including maps and arrays) cannot be returned.|-valign="top"|{{Code|BXCL0005id}}| The id with the specified session is unknown, or has already been closed.|- valign="top"|{{Code|query}}
| An error occurred while evaluating a query. Will only be raised if the XQuery error cannot be extracted from the returned error string.
|-
|{{Code|BXCL0006}}
| A value to be bound is no single item.
|}
=Changelog=
 
;Version 9.0
 
* Updated: error codes updated; errors now use the module namespace
;Version 8.0
* Updated: Values with Bound values may now contain no or more than one item can now be specified in [[#client:query{{Function||client:query]]}}.
;Version 7.5
* Added: [[#client:info{{Function||client:info]]}}
The module was introduced with Version 7.3.
 
[[Category:XQuery]]
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