Class: LibXML::XML::XPath::Context

Inherits:
Object
  • Object
show all
Defined in:
ext/libxml/ruby_xml_xpath_context.c,
ext/libxml/ruby_xml_xpath_context.c

Overview

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')

Instance Method Summary collapse

Constructor Details

#XPath::Context.new(doc) ⇒ XPath::Context

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



77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
 
# File 'ext/libxml/ruby_xml_xpath_context.c', line 77

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

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

  TypedData_Get_Struct(document, xmlDoc, &rxml_document_data_type, xdoc);
  TypedData_Get_Struct(self, rxml_xpath_context, &rxml_xpath_context_data_type, wrapper);

  if (wrapper == NULL)
  {
    wrapper = ALLOC(rxml_xpath_context);
    wrapper->xctxt = NULL;
    wrapper->document = document;
    RTYPEDDATA_DATA(self) = wrapper;
  }
  else if (wrapper->xctxt)
  {
    xmlXPathFreeContext(wrapper->xctxt);
  }

  wrapper->xctxt = xmlXPathNewContext(xdoc);

  return self;
}

Instance Method Details

#disable_cache ⇒ Object

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



378
379
380
381
382
383
384
385
386
387
388
389
390
 
# File 'ext/libxml/ruby_xml_xpath_context.c', line 378

static VALUE
rxml_xpath_context_disable_cache(VALUE self)
{
  rxml_xpath_context *wrapper;
  xmlXPathContextPtr xctxt;
  TypedData_Get_Struct(self, rxml_xpath_context, &rxml_xpath_context_data_type, wrapper);
  xctxt = wrapper->xctxt;

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

  return self;
}

#doc ⇒ Object

Obtain the XML::Document this node belongs to.



113
114
115
116
117
118
119
 
# File 'ext/libxml/ruby_xml_xpath_context.c', line 113

static VALUE rxml_xpath_context_doc(VALUE self)
{
  rxml_xpath_context *wrapper;
  TypedData_Get_Struct(self, rxml_xpath_context, &rxml_xpath_context_data_type, wrapper);
  if (wrapper == NULL) return Qnil;
  return wrapper->document;
}

#enable_cache(size = nil) ⇒ Object

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.



350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
 
# File 'ext/libxml/ruby_xml_xpath_context.c', line 350

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

  TypedData_Get_Struct(self, rxml_xpath_context, &rxml_xpath_context_data_type, wrapper);
  xctxt = wrapper->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

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.

Returns:



309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
 
# File 'ext/libxml/ruby_xml_xpath_context.c', line 309

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

  TypedData_Get_Struct(self, rxml_xpath_context, &rxml_xpath_context_data_type, wrapper);
  xctxt = wrapper->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))
  {
    TypedData_Get_Struct(xpath_expr, xmlXPathCompExpr, &rxml_xpath_expression_data_type, 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(wrapper->document, xctxt, xobject);
}

#node=(node) ⇒ Object

Set the current node used by the XPath engine

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



288
289
290
291
292
293
294
295
296
297
298
299
 
# File 'ext/libxml/ruby_xml_xpath_context.c', line 288

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

  TypedData_Get_Struct(self, rxml_xpath_context, &rxml_xpath_context_data_type, wrapper);
  xctxt = wrapper->xctxt;
  TypedData_Get_Struct(node, xmlNode, &rxml_node_data_type, xnode);
  xctxt->node = xnode;
  return node;
}

#register_namespace(prefix, uri) ⇒ Object

Register the specified namespace URI with the specified prefix in this context.

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



130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
 
# File 'ext/libxml/ruby_xml_xpath_context.c', line 130

static VALUE rxml_xpath_context_register_namespace(VALUE self, VALUE prefix, VALUE uri)
{
  rxml_xpath_context *wrapper;
  xmlXPathContextPtr ctxt;
  TypedData_Get_Struct(self, rxml_xpath_context, &rxml_xpath_context_data_type, wrapper);
  ctxt = wrapper->xctxt;

  /* 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

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')

Returns:

  • (self) 


232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
 
# File 'ext/libxml/ruby_xml_xpath_context.c', line 232

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

  TypedData_Get_Struct(self, rxml_xpath_context, &rxml_xpath_context_data_type, wrapper);
  xctxt = wrapper->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

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)

Returns:

  • (self) 


162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
 
# File 'ext/libxml/ruby_xml_xpath_context.c', line 162

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

  TypedData_Get_Struct(self, rxml_xpath_context, &rxml_xpath_context_data_type, wrapper);
  xctxt = wrapper->xctxt;

  if (rb_obj_is_kind_of(node, cXMLDocument) == Qtrue)
  {
    xmlDocPtr xdoc;
    TypedData_Get_Struct(node, xmlDoc, &rxml_document_data_type, xdoc);
    xnode = xmlDocGetRootElement(xdoc);
  }
  else if (rb_obj_is_kind_of(node, cXMLNode) == Qtrue)
  {
    TypedData_Get_Struct(node, xmlNode, &rxml_node_data_type, 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;
}