From: Rob Boellaard <rboell@...>
Date: 2008-06-08T18:48:11+09:00
Subject: Overwrite a File (rexml)




  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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