From: Robert Klemme <shortcutter@...>
Date: 2011-04-01T17:12:45+09:00
Subject: Re: Can you search in REXML by attributes?

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On Fri, Apr 1, 2011 at 2:53 AM, Kyle X. <haebooty@yahoo.com> wrote:
> Hello and thank you to all the wonderful and helpful people at this
> forum. =A0I am trying to figure out how to search through an XML file and
> grab information. =A0I have been reading the REXML tutorials but could no=
t
> see an answer to my problem in them
> (http://www.germane-software.com/software/rexml/docs/tutorial.html).
> The problem is I need to search by an attribute (in this case the ref)
> and cannot figure out how. =A0Here is a snippet of the XML I am trying to
> extract information from:
>
> <IfcWallStandardCase id=3D"i1677">
> =A0<ObjectPlacement>
> =A0 =A0<IfcLocalPlacement xsi:nil=3D"true" ref=3D"i1671"/>
> =A0</ObjectPlacement>
> </IfcWallStandardCase>
>
> <IfcAxis2Placement3D id=3D"i1671">
> =A0<Location>
> =A0 =A0<IfcCartesianPoint xsi:nil=3D"true" ref=3D"i1667"/>
> =A0</Location>
> </IfcAxis2Placement3D>
>
> <IfcCartesianPoint id=3D"i1667">
> =A0<Coordinates id=3D"i1670" exp:cType=3D"list">
> =A0 =A0<IfcLengthMeasure exp:pos=3D"0">117.4</IfcLengthMeasure>
> =A0 =A0<IfcLengthMeasure exp:pos=3D"1">119.7</IfcLengthMeasure>
> =A0 =A0<IfcLengthMeasure exp:pos=3D"2">0.</IfcLengthMeasure>
> =A0</Coordinates>
> </IfcCartesianPoint>
>
> So basically I have to start with IfcWallStandardCase and from there
> work my way through the "ref"'s until I get to the 3 IfcLengthMeasures.
> I know how to grab the first ref "i1671" using:
> =A0XPath.match(doc,"/IfcWallStandardCase/ObjectPlacement/IfcLocalPlacemen=
t")
> and some additional code.
>
> My problem is I cannot figure out how to use this "i1671" to search the
> xml and grab the next ref. =A0This ref is the only thing linking the item=
s
> together, so it is the only thing that I can use.
>
> Is it possible to search a document by using an attribute, and if so
> how? In this case to use the ref, "i1671" to search the document for
> where it is used as id=3D"i1671" so I can grab the next ref from there an=
d
> so on. =A0Any help would be greatly appreciated.

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?

If the latter you can for example do a BFS.

10:11:30 Temp$ ./rx.rb
--- VISIT:
<IfcAxis2Placement3D id=3D'i1671'>
 <Location>
   <IfcCartesianPoint xsi:nil=3D'true' ref=3D'i1667'/>
 </Location>
</IfcAxis2Placement3D>
--- VISIT:
<IfcCartesianPoint id=3D'i1667'>
 <Coordinates exp:cType=3D'list' id=3D'i1670'>
   <IfcLengthMeasure exp:pos=3D'0'>117.4</IfcLengthMeasure>
   <IfcLengthMeasure exp:pos=3D'1'>119.7</IfcLengthMeasure>
   <IfcLengthMeasure exp:pos=3D'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 =3D REXML::Document.new(DATA.read)
     6
     7  # BFS
     8  queue =3D %w{i1671}
     9
    10  until queue.empty?
    11    id =3D queue.shift
    12
    13    REXML::XPath.each(doc, "//*[@id=3D'#{id}']") do |e|
    14      puts "--- VISIT:", e
    15
    16      REXML::XPath.each(e, './/*[@ref]') do |child|
    17        next_id =3D child.attribute('ref') and queue.push(next_id)
    18      end
    19    end
    20  end
    21
    22  __END__
    23  <root xmlns:exp=3D"http://foo" xmlns:xsi=3D"http://bar">
    24  <IfcWallStandardCase id=3D"i1677">
    25   <ObjectPlacement>
    26     <IfcLocalPlacement xsi:nil=3D"true" ref=3D"i1671"/>
    27   </ObjectPlacement>
    28  </IfcWallStandardCase>
    29
    30  <IfcAxis2Placement3D id=3D"i1671">
    31   <Location>
    32     <IfcCartesianPoint xsi:nil=3D"true" ref=3D"i1667"/>
    33   </Location>
    34  </IfcAxis2Placement3D>
    35
    36  <IfcCartesianPoint id=3D"i1667">
    37   <Coordinates id=3D"i1670" exp:cType=3D"list">
    38     <IfcLengthMeasure exp:pos=3D"0">117.4</IfcLengthMeasure>
    39     <IfcLengthMeasure exp:pos=3D"1">119.7</IfcLengthMeasure>
    40     <IfcLengthMeasure exp:pos=3D"2">0.</IfcLengthMeasure>
    41   </Coordinates>
    42  </IfcCartesianPoint>
    43  </root>
10:11:47 Temp$

Kind regards

robert

--=20
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

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