I'm pretty confused about this one. Given the following xml:
<sch:eventList>
<sch:event>
<sch:eventName>Event One</sch:eventName>
<sch:locationName>Location One</sch:locationName>
</sch:event>
<sch:event>
<sch:eventName>Event Two</sch:eventName>
<sch:locationName>Location Two</sch:locationName>
</sch:event>
</sch:eventList>
When using JDOM using the following code:
XPath eventNameExpression = XPath.newInstance("//sch:eventName");
XPath eventLocationExpression = XPath.newInstance("//sch:eventLocation");
XPath eventExpression = XPath.newInstance("//sch:event");
List<Element> elements = eventExpression.selectNodes(requestElement);
for(Element e: elements) {
System.out.println(eventNameExpression.valueOf(e));
System.out.println(eventLocationExpression.valueOf(e));
}
The console shows this:
Event One
Location One
Event One
Location One
What am I missing?
Don't use '//' it starts always searching at the root node. Use e.g. './sch:eventName' it is relative to the current node.
Related
While trying to help another user out with some question, I ran into the following problem myself:
The object is to find the country of origin of a list of wines on the page. So we start with:
import requests
from lxml import etree
url = "https://www.winepeople.com.au/wines/Dry-Red/_/N-1z13zte"
res = requests.get(url)
content = res.content
res = requests.get(url)
tree = etree.fromstring(content, parser=etree.HTMLParser())
tree_struct = etree.ElementTree(tree)
Next, for reasons I'll get into in a separate question, I'm trying to compare the xpath of two elements with certain attributes. So:
wine = tree.xpath("//div[contains(#class, 'row wine-attributes')]")
country = tree.xpath("//div/text()[contains(., 'Australia')]")
So far, so good. What are we dealing with here?
type(wine),type(country)
>> (list, list)
They are both lists. Let's check the type of the first element in each list:
type(wine[0]),type(country[0])
>> (lxml.etree._Element, lxml.etree._ElementUnicodeResult)
And this is where the problem starts. Because, as mentioned, I need to find the xpath of the first elements of the wine and country lists. And when I run:
tree_struct.getpath(wine[0])
The output is, as expected:
'/html/body/div[13]/div/div/div[2]/div[6]/div[1]/div/div/div[2]/div[2]'
But with the other:
tree_struct.getpath(country[0])
The output is:
TypeError: Argument 'element' has incorrect type (expected
lxml.etree._Element, got lxml.etree._ElementUnicodeResult)
I couldn't find much information about _ElementUnicodeResult), so what is it? And, more importantly, how do I fix the code so that I get an xpath for that node?
You're selecting a text() node instead of an element node. This is why you end up with a lxml.etree._ElementUnicodeResult type instead of a lxml.etree._Element type.
Try changing your xpath to the following in order to select the div element instead of the text() child node of div...
country = tree.xpath("//div[contains(., 'Australia')]")
I’m using Rails 4.2.7 with Nokogiri. I’m having trouble creating a child node. I have the following code
general = doc.xpath("//lomimscc:general")
description = Nokogiri::XML::Node.new "lomimscc:description", doc
string = Nokogiri::XML::Node.new "lomimscc:string", doc
string.content = scenario.abstract
string['language'] = 'en'
description << string
general << description
I want the “description” element to be a child element of the “general” element (and similarly I want the “string” element to be a child of the “description” element). However what is happening is that the description element is appearing as a sibling of the general element. How do I make the element appear as a child instead of a sibling?
The tutorials show how to do this in "Creating new nodes", but the simple example is:
require 'nokogiri'
doc = Nokogiri::XML('<root/>')
doc.at('root').add_child('<foo/>')
doc.to_xml # => "<?xml version=\"1.0\"?>\n<root>\n <foo/>\n</root>\n"
Nokogiri makes it easy to build nodes using a string that contains the markup or nodes you want to add.
You should be able to build upon this easily.
This is also noted throughout the Node documentation any place you see "node_or_tags".
When I changed
general = doc.xpath("//lomimscc:general")
to
general = doc.xpath("//lomimscc:general").first
then everything worked as far as creating child nodes.
Background:
I have an XML document with the following structure:
<body>
<section>content</section>
<section>content</section>
<section>content</section>
<section>content</section>
</body>
Using xpath I want to check if a <section> element is the second element and if so apply some function.
Question:
How do I check if a <section> element is the second element in the body element?
../section[position()=2]
If you want to know if the second element in the body is named section then you can do this:
local-name(/body/child::element()[2]) eq "section"
That will return either true or false.
However, you then asked how can you check this and if it is true, then apply some function. In XPath you cannot author your own functions you can only do that in XQuery or XSLT. So let me for a moment assume you are wishing to call a different XPath function on the value of the second element if it is a section. Here is an example of applying the lower-case function:
if(local-name(/body/child::element()[2]) eq "section")then
lower-case(/body/child::element()[2])
else()
However, this can simplified as lower-case and many other functions take a value with a minimum cardinality of zero. This means that you can just apply the function to a path expression, and if the path did not match anything then the function typically returns an empty sequence, in the same way as a path that did not match will. So, this is semantically equivalent to the above:
lower-case(/body/child::element()[2][local-name(.) eq "section"])
If you are in XQuery or XSLT and are writing your own functions, I would encourage you to write functions that will accept a minimum cardinality of zero, just like lower-case does. By doing this you can chain functions together, and if there is no input data (i.e. from a path expression that does not match anything), these is no output data. This leads to a very nice functional programming style.
Question: How do I check if a element is the second element
in the body element?
Using C#, you can utilize theXPathNodeIterator class in order to traverse the nodes data, and use its CurrentPosition property to investigate the current node position:
XPathNodeIterator.CurrentPosition
Example:
const string xmlStr = #"<body>
<section>1</section>
<section>2</section>
<section>3</section>
<section>4</section>
</body>";
using (var stream = new StringReader(xmlStr))
{
var document = new XPathDocument(stream);
XPathNavigator navigator = document.CreateNavigator();
XPathNodeIterator nodes = navigator.Select("/body/section");
if (nodes.MoveNext())
{
XPathNavigator nodesNavigator = nodes.Current;
XPathNodeIterator nodesText =
nodesNavigator.SelectDescendants(XPathNodeType.Text, false);
while (nodesText.MoveNext())
{
if (nodesText.CurrentPosition == 2)
{
//DO SOMETHING WITH THE VALUE AT THIS POSITION
var currentValue = nodesText.Current.Value;
}
}
}
}
I could not find much examples of evaluate XPath using xerces-c 3.1.
Given the following sample XML input:
<abc>
<def>AAA BBB CCC</def>
</abc>
I need to retrieve the "AAA BBB CCC" string by the XPath "/abc/def/text()[0]".
The following code works:
XMLPlatformUtils::Initialize();
// create the DOM parser
XercesDOMParser *parser = new XercesDOMParser;
parser->setValidationScheme(XercesDOMParser::Val_Never);
parser->parse("test.xml");
// get the DOM representation
DOMDocument *doc = parser->getDocument();
// get the root element
DOMElement* root = doc->getDocumentElement();
// evaluate the xpath
DOMXPathResult* result=doc->evaluate(
XMLString::transcode("/abc/def"), // "/abc/def/text()[0]"
root,
NULL,
DOMXPathResult::ORDERED_NODE_SNAPSHOT_TYPE, //DOMXPathResult::ANY_UNORDERED_NODE_TYPE, //DOMXPathResult::STRING_TYPE,
NULL);
// look into the xpart evaluate result
result->snapshotItem(0);
std::cout<<StrX(result->getNodeValue()->getFirstChild()->getNodeValue())<<std::endl;;
XMLPlatformUtils::Terminate();
return 0;
But I really hate that:
result->getNodeValue()->getFirstChild()->getNodeValue()
Has it to be a node set instead of the exact node I want?
I tried other format of XPath such as "/abc/def/text()[0]", and "DOMXPathResult::STRING_TYPE". xerces always thrown exception.
What did I do wrong?
I don't code with Xerces C++ but it seems to implement the W3C DOM Level 3 so based on that I would suggest to select an element node with a path like /abc/def and then simply to access result->getNodeValue()->getTextContent() to get the contents of the element (e.g. AAA BBB CCC).
As far as I understand the DOM APIs, if you want a string value then you need to use a path like string(/abc/def) and then result->getStringValue() should do (if the evaluate method requests any type or STRING_TYPE as the result type).
Other approaches if you know you are only interested in the first node in document order you could evaluate /abc/def with FIRST_ORDERED_NODE_TYPE and then access result->getNodeValue()->getTextContent().
How can I get H1,H2,H3 contents in one single xpath expression?
I know I could do this.
//html/body/h1/text()
//html/body/h2/text()
//html/body/h3/text()
and so on.
Use:
/html/body/*[self::h1 or self::h2 or self::h3]/text()
The following expression is incorrect:
//html/body/*[local-name() = "h1"
or local-name() = "h2"
or local-name() = "h3"]/text()
because it may select text nodes that are children of unwanted:h1, different:h2, someWeirdNamespace:h3.
Another recommendation: Always avoid using // when the structure of the XML document is statically known. Using // most often results in significant inefficiencies because it causes the complete document (sub)tree roted in the context node to be traversed.