From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2011-04-02T02:19:38+09:00
Subject: Re: Can you search in REXML by attributes?

On Fri, Apr 1, 2011 at 6:27 PM, Kyle X. <haebooty@yahoo.com> wrote:
> Robert K. wrote in post #990336:
>> On Fri, Apr 1, 2011 at 2:53 AM, Kyle X. <haebooty@yahoo.com> wrote:
>>
>> It is not entirely clear what you want.  Do you want to look for all
>> "ref" instances and find elements they are referring to?  Or do you
>> want to do some kind of graph traversal where you start with a
>> particular element and follow every ref attribute?
>
> Hi and thank you for your help.  I am sorry if what I wrote was unclear.
> What my goal is is to start at a given location (in this case-
> <IfcWallStandardCase id="i1677">) and eventually grab the three
> IfcLengthMeasure text values, that are associated with this
> <IfcWallStandardCase id="i1677">, and put them into an array.
>
>> If the latter you can for example do a BFS.
>>
>> 10:11:30 Temp$ ./rx.rb
>> --- VISIT:
>> <IfcAxis2Placement3D id='i1671'>
>>  <Location>
>>    <IfcCartesianPoint xsi:nil='true' ref='i1667'/>
>>  </Location>
>> </IfcAxis2Placement3D>
>> --- VISIT:
>> <IfcCartesianPoint id='i1667'>
>>  <Coordinates exp:cType='list' id='i1670'>
>>    <IfcLengthMeasure exp:pos='0'>117.4</IfcLengthMeasure>
>>    <IfcLengthMeasure exp:pos='1'>119.7</IfcLengthMeasure>
>>    <IfcLengthMeasure exp:pos='2'>0.</IfcLengthMeasure>
>>  </Coordinates>
>> </IfcCartesianPoint>
>> 10:11:43 Temp$ cat -n rx.rb
>>      1  #!/bin/env ruby19
>>      2
>>      3  require 'rexml/document'
>>      4
>>      5  doc = REXML::Document.new(DATA.read)
>>      6
>>      7  # BFS
>>      8  queue = %w{i1671}
>>      9
>>     10  until queue.empty?
>>     11    id = queue.shift
>>     12
>>     13    REXML::XPath.each(doc, "//*[@id='#{id}']") do |e|
>>     14      puts "--- VISIT:", e
>>     15
>>     16      REXML::XPath.each(e, './/*[@ref]') do |child|
>>     17        next_id = child.attribute('ref') and queue.push(next_id)
>>     18      end
>>     19    end
>>     20  end
>>     21
>>     22  __END__
>>     23  <root xmlns:exp="http://foo" xmlns:xsi="http://bar">
>>     24  <IfcWallStandardCase id="i1677">
>>     25   <ObjectPlacement>
>>     26     <IfcLocalPlacement xsi:nil="true" ref="i1671"/>
>>     27   </ObjectPlacement>
>>     28  </IfcWallStandardCase>
>>     29
>>     30  <IfcAxis2Placement3D id="i1671">
>>     31   <Location>
>>     32     <IfcCartesianPoint xsi:nil="true" ref="i1667"/>
>>     33   </Location>
>>     34  </IfcAxis2Placement3D>
>>     35
>>     36  <IfcCartesianPoint id="i1667">
>>     37   <Coordinates id="i1670" exp:cType="list">
>>     38     <IfcLengthMeasure exp:pos="0">117.4</IfcLengthMeasure>
>>     39     <IfcLengthMeasure exp:pos="1">119.7</IfcLengthMeasure>
>>     40     <IfcLengthMeasure exp:pos="2">0.</IfcLengthMeasure>
>>     41   </Coordinates>
>>     42  </IfcCartesianPoint>
>>     43  </root>
>> 10:11:47 Temp$
>
> I will give this a try.
>
>>
>> Kind regards
>>
>> robert
>
> Dear 7stud.  Using the XPath command:
>
> doc = Document.new xml
> target = XPath.match(doc, "//*[@id = 'i1671']")
> p target
>
> It produces the following output as you said it would.
> --output:--
> [<IfcAxis2Placement3D id='i1671'> ... </>]
>
> But I cannot figure out how to do anything with this from here to get to
> the next point, and eventually be able to grab the three values.

I usually use Nokogiri to handle XML documents, and find css selectors
easier than XPath. I'd do it like this:

doc = Nokogiri::XML(<<END
<root xmlns:exp="http://foo" xmlns:xsi="http://bar">
<IfcWallStandardCase id="i1677">
 <ObjectPlacement>
   <IfcLocalPlacement xsi:nil="true" ref="i1671"/>
 </ObjectPlacement>
</IfcWallStandardCase>

<IfcAxis2Placement3D id="i1671">
 <Location>
   <IfcCartesianPoint xsi:nil="true" ref="i1667"/>
 </Location>
</IfcAxis2Placement3D>

<IfcCartesianPoint id="i1667">
 <Coordinates id="i1670" exp:cType="list">
   <IfcLengthMeasure exp:pos="0">117.4</IfcLengthMeasure>
   <IfcLengthMeasure exp:pos="1">119.7</IfcLengthMeasure>
   <IfcLengthMeasure exp:pos="2">0.</IfcLengthMeasure>
 </Coordinates>
</IfcCartesianPoint>
</root>
END
)

reference = doc.css("#i1671 Location IfcCartesianPoint").attribute("ref").value
doc.css("##{reference} Coordinates IfcLengthMeasure").map {|element|
element.text}

This returns: => ["117.4", "119.7", "0."]

I'm pretty sure it's easy to translate these two expressions to XPath,
something like:

reference = REXML::XPath.first(doc,
"//*[@id='i1671']/Location/IfcCartesianPoint").attribute("ref").value
elements = REXML::XPath.match(doc,
"//*[@id='#{reference}']/Coordinates/IfcLengthMeasure").map {|element|
element.text}

don't know if there's a better way, but the above works for me.

Jesus.