class LibXML::XML::XPath::Context

The XML::XPath::Context class is used to evaluate XPath expressions. Generally, you should not directly use this class, but instead use the XML::Document#find and XML::Node#find methods.

doc = XML::Document.string('<header>content</header>')
context = XPath::Context.new(doc)
context.node = doc.root
context.register_namespaces_from_node(doc.root)
nodes = context.find('/header')

Public Class Methods

XPath::Context.new(doc) → XPath::Context click to toggle source

Creates a new XPath context for the specified document. The context can then be used to evaluate an XPath expression.

doc = XML::Document.string('<header><first>hi</first></header>')
context = XPath::Context.new(doc)
nodes = XPath::Object.new('//first', context)
nodes.length == 1

static VALUE rxml_xpath_context_initialize(VALUE self, VALUE document)
{
  xmlDocPtr xdoc;

  if (rb_obj_is_kind_of(document, cXMLDocument) != Qtrue)
  {
    rb_raise(rb_eTypeError, "Supplied argument must be a document or node.");
  }

  Data_Get_Struct(document, xmlDoc, xdoc);
  DATA_PTR(self) = xmlXPathNewContext(xdoc);

  return self;
}

Public Instance Methods

disable_cache click to toggle source

Disables an XPath::Context‘s built-in cache.

static VALUE
rxml_xpath_context_disable_cache(VALUE self)
{
  xmlXPathContextPtr xctxt;
  Data_Get_Struct(self, xmlXPathContext, xctxt);

  if (xmlXPathContextSetCache(xctxt, 0, 0, 0) == -1)
    rxml_raise(xmlGetLastError());

  return self;
}

doc → document click to toggle source

Obtain the XML::Document this node belongs to.

static VALUE rxml_xpath_context_doc(VALUE self)
{
  xmlDocPtr xdoc = NULL;
  xmlXPathContextPtr ctxt;
  Data_Get_Struct(self, xmlXPathContext, ctxt);
  
  xdoc = ctxt->doc;
  return rxml_document_wrap(xdoc);
}

enable_cache(size = nil) click to toggle source

Enables an XPath::Context‘s built-in cache. If the cache is enabled then XPath objects will be cached internally for reuse. The size parameter controls sets the maximum number of XPath objects that will be cached per XPath object type (node-set, string, number, boolean, and misc objects). Set size to nil to use the default cache size of 100.

static VALUE
rxml_xpath_context_enable_cache(int argc,  VALUE *argv, VALUE self)
{
  xmlXPathContextPtr xctxt;
  VALUE size;
  int value = -1;

  Data_Get_Struct(self, xmlXPathContext, xctxt);

  if (rb_scan_args(argc, argv, "01", &size) == 1)
  {
          value = NUM2INT(size);
  }

  if (xmlXPathContextSetCache(xctxt, 1, value, 0) == -1)
    rxml_raise(xmlGetLastError());

  return self;
}

find("xpath") → true|false|number|string|XML::XPath::Object click to toggle source

Executes the provided xpath function. The result depends on the execution of the xpath statement. It may be true, false, a number, a string or a node set.

static VALUE rxml_xpath_context_find(VALUE self, VALUE xpath_expr)
{
  xmlXPathContextPtr xctxt;
  xmlXPathObjectPtr xobject;
  xmlXPathCompExprPtr xcompexpr;

  Data_Get_Struct(self, xmlXPathContext, xctxt);

  if (TYPE(xpath_expr) == T_STRING)
  {
    VALUE expression = rb_check_string_type(xpath_expr);
    xobject = xmlXPathEval((xmlChar*) StringValueCStr(expression), xctxt);
  }
  else if (rb_obj_is_kind_of(xpath_expr, cXMLXPathExpression))
  {
    Data_Get_Struct(xpath_expr, xmlXPathCompExpr, xcompexpr);
    xobject = xmlXPathCompiledEval(xcompexpr, xctxt);
  }
  else
  {
    rb_raise(rb_eTypeError,
        "Argument should be an instance of a String or XPath::Expression");
  }

  return rxml_xpath_to_value(xctxt, xobject);
}

node = node click to toggle source

Set the current node used by the XPath engine

doc = XML::Document.string('<header><first>hi</first></header>')
context.node = doc.root.first

static VALUE rxml_xpath_context_node_set(VALUE self, VALUE node)
{
  xmlXPathContextPtr xctxt;
  xmlNodePtr xnode;

  Data_Get_Struct(self, xmlXPathContext, xctxt);
  Data_Get_Struct(node, xmlNode, xnode);
  xctxt->node = xnode;
  return node;
}

register_namespace(prefix, uri) → (true|false) click to toggle source

context.register_namespace('xi', 'http://www.w3.org/2001/XInclude')

static VALUE rxml_xpath_context_register_namespace(VALUE self, VALUE prefix, VALUE uri)
{
  xmlXPathContextPtr ctxt;
  Data_Get_Struct(self, xmlXPathContext, ctxt);

  /* Prefix could be a symbol. */
  prefix = rb_obj_as_string(prefix);
  
  if (xmlXPathRegisterNs(ctxt, (xmlChar*) StringValuePtr(prefix),
      (xmlChar*) StringValuePtr(uri)) == 0)
  {
    return (Qtrue);
  }
  else
  {
    /* Should raise an exception, IMHO (whose?, why shouldnt it? -danj)*/
    rb_warning("register namespace failed");
    return (Qfalse);
  }
}

register_namespaces(["prefix:uri"]) → self click to toggle source

Register the specified namespaces in this context. There are three different forms that libxml accepts. These include a string, an array of strings, or a hash table:

context.register_namespaces('xi:http://www.w3.org/2001/XInclude')
context.register_namespaces(['xlink:http://www.w3.org/1999/xlink',
                             'xi:http://www.w3.org/2001/XInclude')
context.register_namespaces('xlink' => 'http://www.w3.org/1999/xlink',
                               'xi' => 'http://www.w3.org/2001/XInclude')

static VALUE rxml_xpath_context_register_namespaces(VALUE self, VALUE nslist)
{
  char *cp;
  long i;
  VALUE rprefix, ruri;
  xmlXPathContextPtr xctxt;

  Data_Get_Struct(self, xmlXPathContext, xctxt);

  /* Need to loop through the 2nd argument and iterate through the
   * list of namespaces that we want to allow */
  switch (TYPE(nslist))
  {
  case T_STRING:
    cp = strchr(StringValuePtr(nslist), (int) ':');
    if (cp == NULL)
    {
      rprefix = nslist;
      ruri = Qnil;
    }
    else
    {
      rprefix = rb_str_new(StringValuePtr(nslist), (long) ((intptr_t) cp - (intptr_t)StringValuePtr(nslist)));
      ruri = rxml_new_cstr((const xmlChar*)&cp[1], xctxt->doc->encoding);
    }
    /* Should test the results of this */
    rxml_xpath_context_register_namespace(self, rprefix, ruri);
    break;
  case T_ARRAY:
    for (i = 0; i < RARRAY_LEN(nslist); i++)
    {
      rxml_xpath_context_register_namespaces(self, RARRAY_PTR(nslist)[i]);
    }
    break;
  case T_HASH:
    rb_hash_foreach(nslist, iterate_ns_hash, self);
    break;
  default:
    rb_raise(
        rb_eArgError,
        "Invalid argument type, only accept string, array of strings, or an array of arrays");
  }
  return self;
}

register_namespaces_from_node(node) → self click to toggle source

Helper method to read in namespaces defined on a node.

doc = XML::Document.string('<header><first>hi</first></header>')
context = XPath::Context.new(doc)
context.register_namespaces_from_node(doc.root)

static VALUE rxml_xpath_context_register_namespaces_from_node(VALUE self,
    VALUE node)
{
  xmlXPathContextPtr xctxt;
  xmlNodePtr xnode;
  xmlNsPtr *xnsArr;

  Data_Get_Struct(self, xmlXPathContext, xctxt);

  if (rb_obj_is_kind_of(node, cXMLDocument) == Qtrue)
  {
    xmlDocPtr xdoc;
    Data_Get_Struct(node, xmlDoc, xdoc);
    xnode = xmlDocGetRootElement(xdoc);
  }
  else if (rb_obj_is_kind_of(node, cXMLNode) == Qtrue)
  {
    Data_Get_Struct(node, xmlNode, xnode);
  }
  else
  {
    rb_raise(rb_eTypeError, "The first argument must be a document or node.");
  }

  xnsArr = xmlGetNsList(xnode->doc, xnode);

  if (xnsArr)
  {
    xmlNsPtr xns = *xnsArr;

    while (xns)
    {
      /* If there is no prefix, then this is the default namespace.
       Skip it for now. */
      if (xns->prefix)
      {
        VALUE prefix = rxml_new_cstr(xns->prefix, xctxt->doc->encoding);
        VALUE uri = rxml_new_cstr(xns->href, xctxt->doc->encoding);
        rxml_xpath_context_register_namespace(self, prefix, uri);
      }
      xns = xns->next;
    }
    xmlFree(xnsArr);
  }

  return self;
}