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REXML Element exists question

John Butler

8/30/2007 9:35:00 AM

An xml file is generated and i am currently parsing through it in a
rails app. The problem with this XML file is sometimes the elelment
doesnt have a value it sometimes doesnt include the tags in the file.
So for example:

If it has a value
<Client>Client Name</Client>

An empty value
<Client></Client>

Sometimes i wont even have the above tags depending on how the file was
generated from a different application.

I want to check if the Client element is present in the file so the
following code below works somehow:

if !element.elements["Client"].nil?
project.client = element.elements["Client"].text
end

My question is there a more elegant way to this? I dont want to have to
write an if/case statment for every possible element. I did try the
below but that gave me an error on the nil? because it couldnt find the
element to test if it was nil, thats why im suprised the above code
works.

!element.elements["Client"].nil ? project.client =
element.elements["Client"].text : project.client = nil


I have looked at the rexml docs for elements, attributes but nothing
works if the <client></client> tags are not present.

Any advice appreciated,

JB
--
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4 Answers

Urban Hafner

8/30/2007 11:27:00 AM

0

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On Aug 30, 2007, at 12:35 , John Butler wrote:

> My question is there a more elegant way to this? I dont want to
> have to
> write an if/case statment for every possible element. I did try the
> below but that gave me an error on the nil? because it couldnt find
> the
> element to test if it was nil, thats why im suprised the above code
> works.
>
> !element.elements["Client"].nil ? project.client =
> element.elements["Client"].text : project.client = nil

I have no idea of REXML but you are missing a ? here. The one present is
the one of the ?: operator, but you need the .nil? method and not the
nil method so you have to add a second one.

And if everything works like the above (i.e. the XML Tag has the same
name as the model attribute) then you could use something like this
(untested of course) and maybe stick it into a method:

e = "Client"
meth = "#{e.downcase}=".to_sym
text = !element.elements[e].nil? ? element.elements[e].text : nil
project.send(meth, text)

Urban





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Robert Klemme

8/30/2007 9:16:00 PM

0

On 30.08.2007 11:35, John Butler wrote:
> An xml file is generated and i am currently parsing through it in a
> rails app. The problem with this XML file is sometimes the elelment
> doesnt have a value it sometimes doesnt include the tags in the file.
> So for example:
>
> If it has a value
> <Client>Client Name</Client>
>
> An empty value
> <Client></Client>
>
> Sometimes i wont even have the above tags depending on how the file was
> generated from a different application.
>
> I want to check if the Client element is present in the file so the
> following code below works somehow:

This should do what you need:

doc = REXML::Document.new(File.read(f))
cl = REXML::XPath.first(doc, '//Client')
project.client = cl.text if cl

> if !element.elements["Client"].nil?
> project.client = element.elements["Client"].text
> end
>
> My question is there a more elegant way to this? I dont want to have to
> write an if/case statment for every possible element. I did try the
> below but that gave me an error on the nil? because it couldnt find the
> element to test if it was nil, thats why im suprised the above code
> works.
>
> !element.elements["Client"].nil ? project.client =
> element.elements["Client"].text : project.client = nil
>
>
> I have looked at the rexml docs for elements, attributes but nothing
> works if the <client></client> tags are not present.

IMHO the REXML tutorial is great source:
http://www.germane-software.com/software/rexml/docs/tut...

I also often look at
http://www.w3schools....
http://www.zvon.org/xxl/XPathTutorial/General/exa...

Kind regards

robert

Dejan Dimic

8/30/2007 9:36:00 PM

0

You should consider using XPaths capabilities of REXML.

http://stdlib.rubyonrails.org/libdoc/rexml/rdoc/...
http://www.ruby-doc.org/stdlib/libdoc/rexml/rdoc/classes/REXML/...
http://www.ibm.com/developerworks/xml/library/x-matt...
http://www.germane-software.com/software/rexml/docs/tut...




On Aug 30, 1:26 pm, Urban Hafner <ur...@bettong.net> wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On Aug 30, 2007, at 12:35 , John Butler wrote:
>
> > My question is there a more elegant way to this? I dont want to
> > have to
> > write an if/case statment for every possible element. I did try the
> > below but that gave me an error on the nil? because it couldnt find
> > the
> > element to test if it was nil, thats why im suprised the above code
> > works.
>
> > !element.elements["Client"].nil ? project.client =
> > element.elements["Client"].text : project.client = nil
>
> I have no idea of REXML but you are missing a ? here. The one present is
> the one of the ?: operator, but you need the .nil? method and not the
> nil method so you have to add a second one.
>
> And if everything works like the above (i.e. the XML Tag has the same
> name as the model attribute) then you could use something like this
> (untested of course) and maybe stick it into a method:
>
> e = "Client"
> meth = "#{e.downcase}=".to_sym
> text = !element.elements[e].nil? ? element.elements[e].text : nil
> project.send(meth, text)
>
> Urban
>
> -----BEGIN PGP SIGNATURE-----
> Version: GnuPG v1.4.6 (Darwin)
>
> iD8DBQFG1qlsggNuVCIrEyURAp38AJ4y76fXMtYgKRA60ovmpdz0kuXt6QCfbtqr
> 2SBTn6C4TlP/iCdQt14WJXI=
> =YWwN
> -----END PGP SIGNATURE-----

John Butler

8/31/2007 7:40:00 PM

0

dima wrote:
> You should consider using XPaths capabilities of REXML.
>
> http://stdlib.rubyonrails.org/libdoc/rexml/rdoc/...
> http://www.ruby-doc.org/stdlib/libdoc/rexml/rdoc/classes/REXML/...
> http://www.ibm.com/developerworks/xml/library/x-matt...
> http://www.germane-software.com/software/rexml/docs/tut...

Thanks for the advice,

Yes xpath is definately the way to go.

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