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Overwrite a File (rexml)

 
 
Rob Boellaard
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Posts: n/a
 
      06-08-2008



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:efault.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:efault.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
--
Posted via http://www.ruby-forum.com/.

 
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Robert Klemme
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Posts: n/a
 
      06-09-2008
2008/6/8 Rob Boellaard <(E-Mail Removed)>:
>
>
>
> 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:efault.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:efault.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,


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


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

 
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Une Bévue
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Posts: n/a
 
      06-09-2008
Rob Boellaard <(E-Mail Removed)> 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:


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[@id = 'maj']", {"xhtml" =>
"http://www.w3.org/1999/xhtml"}).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[@id = 'maj']\" for file '#{file}'!"
end
end

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