How to access nested XML with Nokogiri [closed] - ruby-on-rails

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I am using Nokogiri to parse XML. I was told to use a CSS selector to search through the XML, but I can't chain it to get through the nested objects.
How do I access the inner elements?
2.6.3 :039 > pp a.css("interface").to_s
"<interface>\n" +
" <status>\n" +
" <__XML__OPT_Cmd_show_interface_status_down>\n" +
" <__XML__OPT_Cmd_show_interface_status___readonly__>\n" +
" <__readonly__>\n" +
" <TABLE_interface>\n" +
" <ROW_interface>\n" +
" <interface>mgmt0</interface>\n" +
" <state>connected</state>\n" +
" <vlan>routed</vlan>\n" +
" <duplex>full</duplex>\n" +
" <speed>a-1000</speed>\n" +
" <type>--</type>\n" +
" </ROW_interface>\n" +
" <ROW_interface>\n" +
" <interface>Vlan1</interface>\n" +
" <state>down</state>\n" +
" <vlan>routed</vlan>\n" +
" <duplex>auto</duplex>\n" +
" <speed>auto</speed>\n" +
" </ROW_interface>\n" +
" <ROW_interface>\n" +
" <interface>Vlan6</interface>\n" +
" <state>down</state>\n" +
" <vlan>routed</vlan>\n" +
" <duplex>auto</duplex>\n" +
" <speed>auto</speed>\n" +
" </ROW_interface>\n" +
" <ROW_interface>\n" +
" <interface>Vlan486</interface>\n" +
" <state>down</state>\n" +
" <vlan>routed</vlan>\n" +
" <duplex>auto</duplex>\n" +
" <speed>auto</speed>\n" +
" </ROW_interface>\n" +
" </TABLE_interface>\n" +
" </__readonly__>\n" +
" </__XML__OPT_Cmd_show_interface_status___readonly__>\n" +
" </__XML__OPT_Cmd_show_interface_status_down>\n" +
" </status>\n" +
" </interface><interface>mgmt0</interface><interface>Vlan1</interface><interface>Vlan6</interface><interface>Vlan486</interface>"
I end up with this tree. What is my XPath here? This is only part of the parsed XML:
2.6.3 :043 > pp parsed
#(DocumentFragment:0x3fce080cd300 {
name = "#document-fragment",
children = [
#(ProcessingInstruction:0x3fce080cce14 { name = "xml" }),
#(Text "\n"),
#(Element:0x3fce080cc7d4 {
name = "rpc-reply",
namespace = #(Namespace:0x3fce080cffb0 {
prefix = "nf",
href = "urn:ietf:params:xml:ns:netconf:base:1.0"
}),
children = [
#(Text "\n" + " "),
#(Element:0x3fce080cf22c {
name = "data",
namespace = #(Namespace:0x3fce080cffb0 {
prefix = "nf",
href = "urn:ietf:params:xml:ns:netconf:base:1.0"
}),
children = [
#(Text "\n" + " "),
#(Element:0x1903f98 {
name = "show",
namespace = #(Namespace:0x1903f20 {
href = "http://www.cisco.com/nxos:1.0:if_manager"
}),
children = [
#(Text "\n" + " "),
#(Element:0x1903700 {
name = "interface",
namespace = #(Namespace:0x1903f20 {
href = "http://www.cisco.com/nxos:1.0:if_manager"
}),
children = [
#(Text "\n" + " "),
#(Element:0x19030fc {
name = "status",
namespace = #(Namespace:0x1903f20 {
href = "http://www.cisco.com/nxos:1.0:if_manager"
}),
children = [
#(Text "\n" + " "),
#(Element:0x1902a1c {
name = "__XML__OPT_Cmd_show_interface_status_down",
namespace = #(Namespace:0x1903f20 {
href = "http://www.cisco.com/nxos:1.0:if_manager"
}),

Answer 1

Your question is really generic and poorly asked so answering a specific question is not possible, but it looks like you need to understand how to access tags in a document using a CSS accessor, which Nokogiri makes very easy.
Meditate on this:
require 'nokogiri'
foo =<<EOT
<tag1>
<tag2>some text</tag2>
<tag3>some more text</tag3>
<tags>something</tags>
<tags>or</tags>
<tags>other</tags>
</tag1>
EOT
xml = Nokogiri::XML.parse(foo)
at finds the first matching occurrence in the document:
xml.at('tag2').content # => "some text"
at is pretty smart, in that it tries to determine whether the accessor is CSS or XPath, so it's a good first tool when you want the first match. If that doesn't work then you can try at_css which specifies that accessor is CSS, because sometimes you can come up with something that could work as CSS or XPath but return different results:
xml.at_css('tag3').content # => "some more text"
xml.at_css('tag3').text # => "some more text"
Similar to at is search, which also tries to determine whether it's CSS or XPath, but finds all matching nodes throughout the document rather than just the first matching one. Because it returns all matching nodes, it returns a NodeSet, unlike at which returns a Node, so you have to be aware that NodeSets behave differently than Nodes when accessing their content or text:
xml.search('tags').text # => "somethingorother"
That's almost never what you want, but you'd be surprised how many people then ask how to split that resulting string into the desired three words. It's usually impossible to do accurately, so a different tactic is needed:
xml.search('tags').map { |t| t.content } # => ["something", "or", "other"]
xml.search('tags').map { |t| t.text } # => ["something", "or", "other"]
xml.search('tags').map(&:text) # => ["something", "or", "other"]
Both at and search have ..._css and ..._xpath variations to help you fine-tune your code's behavior, but I always recommend starting with the generic at and search until you're forced to define what the accessor is.
I also recommend starting with CSS accessors over XPath because they tend to be more readable, and more easily learned if you're working inside HTML with CSS. XPath is very powerful, probably still more so than CSS, but learning it takes longer and often results in less readable code, which affects maintainability.
This is all in the tutorials and cheat sheets and documentation. Nokogiri is extremely powerful but it takes time reading and trying things to learn it. You can also search on SO for other things I've written about searching XML and HTML documents; In particular "What are some examples of using Nokogiri?" helps get an idea how to scrape a page. There's a lot of information covering many different topics related to this. I find it an interesting exercise to parse documents like this as it was part of my professional life for years.

Answer 2

You could use xpath:
parsed = Nokogiri::XML::DocumentFragment.parse(xml)
siamese_cat = parsed.xpath(.//interface/status/state)
Or just iterating thru XML
parsed = Nokogiri::XML::DocumentFragment.parse(xml)
parsed.each do |element|
# Some instructions
end