Asp Forum - REXML and Date interaction

Robert Evans

11/26/2006 9:50:00 PM

Hi,

I have a problem parsing dates from XML. I have this little program
which produces an error, and I was able to fix it by moving the date
parsing into a class that is distinct from the xml processing. Below
is a broken version and the error it prints, and then a working
version with the correct output. I would be grateful if anyone could
explain what is going wrong here. It looks like it turns the class
Date into a string Constant.

Thanks,
Bob Evans

Broken Version
===========

#!/usr/bin/env ruby

require 'rexml/document'
require 'date'

class DateFun

def parse(xml)
doc = REXML::Document.new(xml)
elems = doc.root.get_elements('//body/dateelement[@date]')
elems.map { |s|
s.attributes["date"].to_s
}.sort
end

def sorted_dates_from(xml)
sorted_dates = parse(xml)
sorted_dates.map { |d| Date.parse(d)}.sort
end
end

xmlDates = <<HERE
<body><dateelement date="12/28/1973"/><dateelement date="02/06/1970"/
><dateelement date="02/05/1954"/></body>
HERE

sorted_dates = DateFun.new.sorted_dates_from(xmlDates)
sorted_dates.each { |d| puts d.to_s}

Produces
===========
NoMethodError: undefined method `parse' for "2005/224":String
from /Users/bobevans/Documents/projects/rubyplay/brokendate.rb:18:in
`sorted_dates_from'
from /Users/bobevans/Documents/projects/rubyplay/brokendate.rb:18:in
`sorted_dates_from'
from /Users/bobevans/Documents/projects/rubyplay/brokendate.rb:26
from (irb):1835
from /usr/local/lib/ruby/1.8/rexml/element.rb:1182

Working Version
============
#!/usr/bin/env ruby

require 'rexml/document'
require 'date'

class DateFun
include REXML

def parse(xml)
doc = Document.new(xml)
elems = doc.root.get_elements('//body/dateelement[@date]')
elems.map { |s|
s.attributes["date"].to_s
}.sort
end
end

class Other
def sorted_dates_from(xml)
sorted_dates = DateFun.new.parse(xml)
sorted_dates.map { |d| Date.parse(d)}.sort
end
end

xmlDates = <<HERE
<body><dateelement date="12/28/1973"/><dateelement date="02/06/1970"/
><dateelement date="02/05/1954"/></body>
HERE

sorted_dates = Other.new.sorted_dates_from(xmlDates)
sorted_dates.each { |d| puts d.to_s}

Produces:

1954-02-05
1970-02-06
1973-12-28

5 Answers

dblack

11/26/2006 9:54:00 PM

Robert Evans

11/26/2006 10:14:00 PM

Hi,

Thanks for running it, indeed that broken version works, and I
must've corrupted my irb session. So, I tried it again and discovered
more precisely the problem. If I include REXML in the class instead
of explicitly specifying REXML::Document, then I get the problem.
Which, I can just "not do that" for now, but it is still curious what
is happening. Here is a version that seems to produce the error still.

Thanks for the sanity check,

Bob Evans

Better Broken
=============
#!/usr/bin/env ruby

require 'rexml/document'
require 'date'

class DateFun
## BEGIN Different
include REXML
## END Different

def parse(xml)
## BEGIN Different
doc = Document.new(xml)
##End Different

elems = doc.root.get_elements('//body/dateelement[@date]')
elems.map { |s|
s.attributes["date"].to_s
}.sort
end

def sorted_dates_from(xml)
sorted_dates = parse(xml)
sorted_dates.map { |d| Date.parse(d)}.sort
end
end

xmlDates = <<HERE
<body><dateelement date="12/28/1973"/><dateelement date="02/06/1970"/
><dateelement date="02/05/1954"/></body>
HERE

sorted_dates = DateFun.new.sorted_dates_from(xmlDates)
sorted_dates.each { |d| puts d.to_s}

Produces
===============
/brokendate.rb
/brokendate.rb:18:in `sorted_dates_from': undefined method `parse'
for "2005/224":String (NoMethodError)
from ./brokendate.rb:18:in `sorted_dates_from'
from ./brokendate.rb:26

On Nov 26, 2006, at 1:54 PM, dblack@wobblini.net wrote:

> Hi --
>
> On Mon, 27 Nov 2006, Robert Evans wrote:
>
>> Hi,
>>
>> I have a problem parsing dates from XML. I have this little
>> program which produces an error, and I was able to fix it by
>> moving the date parsing into a class that is distinct from the xml
>> processing. Below is a broken version and the error it prints, and
>> then a working version with the correct output. I would be
>> grateful if anyone could explain what is going wrong here. It
>> looks like it turns the class Date into a string Constant.
>
> Your broken version worked for me. What version of Ruby are you
> using?
>
>
> David
>
> --
> David A. Black | dblack@wobblini.net
> Author of "Ruby for Rails" [1] | Ruby/Rails training &
> consultancy [3]
> DABlog (DAB's Weblog) [2] | Co-director, Ruby Central,
> Inc. [4]
> [1] http://www.manning... | [3] http://
> www.rubypowerandlight.com
> [2] http://dablog.r... | [4] http://www.rubyc...
>

dblack

11/26/2006 10:23:00 PM

Robert Evans

11/26/2006 10:28:00 PM

On Nov 26, 2006, at 2:22 PM, dblack@wobblini.net wrote:

>
> What's happening is that you're bringing REXML::Date into scope. You
> need to do:
>
> ::Date.parse
>
> to get the top-level Date constant.
>
>
> David

Ah cool. I didn't realize there was a REXML::Date class, but I
suspected it might be something like that, and I didn't realize I
could do just ::Date to fully qualify top level modules.

Thanks,
Bob Evans

dblack

11/26/2006 10:44:00 PM

comp.lang.ruby

REXML and Date interaction

Robert Evans

dblack

Robert Evans

dblack

Robert Evans

dblack

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