Overwrite a File (rexml)

ruby-talk
1

Hello,

  I am trying to get some simple create/update/delete xml-element to
work with REXML, but I run into trouble when writing to file. Here's a
code example:

  def save
    file = File.open(@@filePath, "r+")
    doc = Document.new(file)
    root = doc.root

                #create/update/delete elements in the root

          file.rewind
    formatter = REXML::Formatters::Default.new( 5 )
    formatter.write( doc, file)
    file.close

  end

  at first I was just adding and updating, and I noticed I needed to put
the line:
          file.rewind
  or it would just append the root elements to the existing ones in the
file, thereby creating doubles.
  Now that I have reached delete, I get the following behaviour:

  say the file contains:

  element_1
  element_2
  element_3
  element_4

  and I want to delete element_2, the result in the file is:

  element_1
  element_3
  element_4
  element_4

  to me, this:
     formatter.write( doc, file)
  implies that the entire xml doc would be written to the file, and as a
result the file should only contain the doc (or the root of the doc),
and nothing else.

  I am not very experienced in Ruby, and tried to resolve this way:

  def save
    file = File.open(@@filePath, "r+")
    doc = Document.new(file)
    root = doc.root
    file.close

                #create/update/delete elements in the root

    file = File.open(@@filePath, "w")
    formatter = REXML::Formatters::Default.new( 5 )
    formatter.write( doc, file)
    file.close

  end

  this works, but I feel there should be a better approach, because
having to open the same file twice seems awkward .

  Thanks in advance,

  Rob

···

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2

IMHO you need to seek and truncate the file when opened in rw mode.
Otherwise you do not have control about where the document is written.
Since you are first reading it it is likely that the new content
simply gets appended. HTH

Kind regards

robert

···

2008/6/8 Rob Boellaard <rboell@tuparev.com>:

Hello,

I am trying to get some simple create/update/delete xml-element to
work with REXML, but I run into trouble when writing to file. Here's a
code example:

def save
   file = File.open(@@filePath, "r+")
   doc = Document.new(file)
   root = doc.root

               #create/update/delete elements in the root

         file.rewind
   formatter = REXML::Formatters::Default.new( 5 )
   formatter.write( doc, file)
   file.close

end

at first I was just adding and updating, and I noticed I needed to put
the line:
         file.rewind
or it would just append the root elements to the existing ones in the
file, thereby creating doubles.
Now that I have reached delete, I get the following behaviour:

say the file contains:

element_1
element_2
element_3
element_4

and I want to delete element_2, the result in the file is:

element_1
element_3
element_4
element_4

to me, this:
    formatter.write( doc, file)
implies that the entire xml doc would be written to the file, and as a
result the file should only contain the doc (or the root of the doc),
and nothing else.

I am not very experienced in Ruby, and tried to resolve this way:

def save
   file = File.open(@@filePath, "r+")
   doc = Document.new(file)
   root = doc.root
   file.close

               #create/update/delete elements in the root

   file = File.open(@@filePath, "w")
   formatter = REXML::Formatters::Default.new( 5 )
   formatter.write( doc, file)
   file.close

end

this works, but I feel there should be a better approach, because
having to open the same file twice seems awkward .

Thanks in advance,

--
use.inject do |as, often| as.you_can - without end

3

instead of using rexml, I'd suggest you 'xml/smart' which as a "modify"
method.

for example I'm using :
      XML::Smart.modify( "#{file}" ) do | doc |
        node=doc.root.find("//xhtml:p[@id = 'maj']", {"xhtml" =>
"http://www.w3.org/1999/xhtml&quot;\}).first
        if node
          node.text=File.stat("#{file}").mtime.strftime("màj le %d %m %y
%H:%M")
          puts "file '#{file}' updated!"
        else
          puts "No node \"//xhtml:p[@id = 'maj']\" for file '#{file}'!"
        end
      end

in order to modify the date (writen in <p id='maj'><</p>) from file's
mtime.

···

Rob Boellaard <rboell@tuparev.com> wrote:

  I am trying to get some simple create/update/delete xml-element to
work with REXML, but I run into trouble when writing to file. Here's a
code example:

--
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