| XML::LibXML::XPathContext - XPath Evaluation |
XML::LibXML::XPathContext - XPath Evaluation
my $xpc = XML::LibXML::XPathContext->new(); my $xpc = XML::LibXML::XPathContext->new($node); $xpc->registerNs($prefix, $namespace_uri) $xpc->unregisterNs($prefix) $uri = $xpc->lookupNs($prefix) $xpc->registerVarLookupFunc($callback, $data) $data = $xpc->getVarLookupData(); $callback = $xpc->getVarLookupFunc(); $xpc->unregisterVarLookupFunc($name); $xpc->registerFunctionNS($name, $uri, $callback) $xpc->unregisterFunctionNS($name, $uri) $xpc->registerFunction($name, $callback) $xpc->unregisterFunction($name) @nodes = $xpc->findnodes($xpath) @nodes = $xpc->findnodes($xpath, $context_node ) $nodelist = $xpc->findnodes($xpath, $context_node ) $object = $xpc->find($xpath ) $object = $xpc->find($xpath, $context_node ) $value = $xpc->findvalue($xpath ) $value = $xpc->findvalue($xpath, $context_node ) $bool = $xpc->exists( $xpath_expression, $context_node ); $xpc->setContextNode($node) my $node = $xpc->getContextNode; $xpc->setContextPosition($position) my $position = $xpc->getContextPosition; $xpc->setContextSize($size) my $size = $xpc->getContextSize; $xpc->setContextNode($node)
The XML::LibXML::XPathContext class provides an almost complete interface to libxml2's XPath implementation. With XML::LibXML::XPathContext, it is possible to evaluate XPath expressions in the context of arbitrary node, context size, and context position, with a user-defined namespace-prefix mapping, custom XPath functions written in Perl, and even a custom XPath variable resolver.
This example demonstrates registerNs() method. It finds all paragraph nodes in an XHTML document.
my $xc = XML::LibXML::XPathContext->new($xhtml_doc);
$xc->registerNs('xhtml', 'http://www.w3.org/1999/xhtml');
my @nodes = $xc->findnodes('//xhtml:p');
This example demonstrates registerFunction() method by defining a function filtering nodes based on a Perl regular
expression:
sub grep_nodes {
my ($nodelist,$regexp) = @_;
my $result = XML::LibXML::NodeList->new;
for my $node ($nodelist->get_nodelist()) {
$result->push($node) if $node->textContent =~ $regexp;
}
return $result;
};
my $xc = XML::LibXML::XPathContext->new($node);
$xc->registerFunction('grep_nodes', \&grep_nodes);
my @nodes = $xc->findnodes('//section[grep_nodes(para,"\bsearch(ing|es)?\b")]');
This example demonstrates registerVarLookup() method. We use XPath variables to recycle results of previous evaluations:
sub var_lookup {
my ($varname,$ns,$data)=@_;
return $data->{$varname};
}
my $areas = XML::LibXML->new->parse_file('areas.xml');
my $empl = XML::LibXML->new->parse_file('employees.xml');
my $xc = XML::LibXML::XPathContext->new($empl);
my %variables = (
A => $xc->find('/employees/employee[@salary>10000]'),
B => $areas->find('/areas/area[district='Brooklyn']/street'),
);
# get names of employees from $A working in an area listed in $B
$xc->registerVarLookupFunc(\&var_lookup, \%variables);
my @nodes = $xc->findnodes('$A[work_area/street = $B]/name');
my $xpc = XML::LibXML::XPathContext->new();
Creates a new XML::LibXML::XPathContext object without a context node.
my $xpc = XML::LibXML::XPathContext->new($node);
Creates a new XML::LibXML::XPathContext object with the context node set to $node.
$xpc->registerNs($prefix, $namespace_uri)
Registers namespace $prefix to $namespace_uri.
$xpc->unregisterNs($prefix)
Unregisters namespace $prefix.
$uri = $xpc->lookupNs($prefix)
Returns namespace URI registered with $prefix. If $prefix is not registered to any namespace URI returns undef.
$xpc->registerVarLookupFunc($callback, $data)
Registers variable lookup function $prefix. The registered function is executed by the XPath engine each time an XPath
variable is evaluated. It takes three arguments: $data, variable name, and variable ns-URI and must return one value: a number or
string or any XML::LibXML:: object that can be a result of findnodes: Boolean, Literal, Number, Node (e.g.
Document, Element, etc.), or NodeList. For convenience, simple (non-blessed)
array references containing only the XML::LibXML::Node manpage objects can be used instead of an the XML::LibXML::NodeList manpage.
$data = $xpc->getVarLookupData();
Returns the data that have been associated with a variable lookup function
during a previous call to registerVarLookupFunc.
$callback = $xpc->getVarLookupFunc();
Returns the variable lookup function previously registered with registerVarLookupFunc.
$xpc->unregisterVarLookupFunc($name);
Unregisters variable lookup function and the associated lookup data.
$xpc->registerFunctionNS($name, $uri, $callback)
Registers an extension function $name in $uri namespace. $callback must be a CODE reference. The arguments of the callback function are either
simple scalars or XML::LibXML::* objects depending on the XPath argument types. The function is responsible for
checking the argument number and types. Result of the callback code must be a
single value of the following types: a simple scalar (number, string) or an
arbitrary XML::LibXML::* object that can be a result of findnodes: Boolean, Literal, Number, Node (e.g.
Document, Element, etc.), or NodeList. For convenience, simple (non-blessed)
array references containing only the XML::LibXML::Node manpage objects can be used instead of a the XML::LibXML::NodeList manpage.
$xpc->unregisterFunctionNS($name, $uri)
Unregisters extension function $name in $uri namespace. Has the same effect as passing undef as $callback to registerFunctionNS.
$xpc->registerFunction($name, $callback)
Same as registerFunctionNS but without a namespace.
$xpc->unregisterFunction($name)
Same as unregisterFunctionNS but without a namespace.
@nodes = $xpc->findnodes($xpath)
@nodes = $xpc->findnodes($xpath, $context_node )
$nodelist = $xpc->findnodes($xpath, $context_node )
Performs the xpath statement on the current node and returns the result as an array. In scalar context, returns an the XML::LibXML::NodeList manpage object. Optionally, a node may be passed as a second argument to set the context node for the query.
The xpath expression can be passed either as a string, or as a the XML::LibXML::XPathExpression manpage object.
$object = $xpc->find($xpath )
$object = $xpc->find($xpath, $context_node )
Performs the xpath expression using the current node as the context of the
expression, and returns the result depending on what type of result the XPath
expression had. For example, the XPath 1 * 3 + 52 results in an the XML::LibXML::Number manpage object being returned. Other expressions might return a the XML::LibXML::Boolean manpage object, or a the XML::LibXML::Literal manpage object (a string). Each of those objects uses Perl's overload feature to ``do
the right thing'' in different contexts. Optionally, a node may be passed as a
second argument to set the context node for the query.
The xpath expression can be passed either as a string, or as a the XML::LibXML::XPathExpression manpage object.
$value = $xpc->findvalue($xpath )
$value = $xpc->findvalue($xpath, $context_node )
Is exactly equivalent to:
$xpc->find( $xpath, $context_node )->to_literal;
That is, it returns the literal value of the results. This enables you to ensure that you get a string back from your search, allowing certain shortcuts. This could be used as the equivalent of <xsl:value-of select=``some_xpath''/>. Optionally, a node may be passed in the second argument to set the context node for the query.
The xpath expression can be passed either as a string, or as a the XML::LibXML::XPathExpression manpage object.
$bool = $xpc->exists( $xpath_expression, $context_node );
This method behaves like findnodes >>>>>, except that it only returns a boolean value (1 if the expression matches a node, 0 otherwise) and may be faster than findnodes >>>>>, because the XPath evaluation may stop early on the first match (this is true for libxml2 >= 2.6.27).
For XPath expressions that do not return node-set, the method returns true if the returned value is a non-zero number or a non-empty string.
$xpc->setContextNode($node)
Set the current context node.
my $node = $xpc->getContextNode;
Get the current context node.
$xpc->setContextPosition($position)
Set the current context position. By default, this value is -1 (and evaluating
XPath function position() in the initial context raises an XPath error), but can be set to any value up
to context size. This usually only serves to cheat the XPath engine to return
given position when position() XPath function is called. Setting this value to -1 restores the default
behavior.
my $position = $xpc->getContextPosition;
Get the current context position.
$xpc->setContextSize($size)
Set the current context size. By default, this value is -1 (and evaluating
XPath function last() in the initial context raises an XPath error), but can be set to any
non-negative value. This usually only serves to cheat the XPath engine to
return the given value when last() XPath function is called. If context size is set to 0, position is
automatically also set to 0. If context size is positive, position is
automatically set to 1. Setting context size to -1 restores the default
behavior.
my $size = $xpc->getContextSize;
Get the current context size.
$xpc->setContextNode($node)
Set the current context node.
XML::LibXML::XPathContext objects are >>>>> reentrant, meaning that you can call methods of an XML::LibXML::XPathContext even from XPath extension functions registered with the same object or from a variable lookup function. On the other hand, you should rather avoid registering new extension functions, namespaces and a variable lookup function from within extension functions and a variable lookup function, unless you want to experience untested behavior.
Ilya Martynov and Petr Pajas, based on XML::LibXML and XML::LibXSLT code by Matt Sergeant and Christian Glahn.
Prior to XML::LibXML 1.61 this module was distributed separately for maintenance reasons.
Matt Sergeant, Christian Glahn, Petr Pajas
2.0201
2001-2007, AxKit.com Ltd.
2002-2006, Christian Glahn.
2006-2009, Petr Pajas.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
| XML::LibXML::XPathContext - XPath Evaluation |