DZone Snippets: elements code

Adding helpful error messages to your Ruby code

jrobertson (James Robertson) — Wed, 30 Apr 2008 11:40:47 GMT

This Ruby code raises an error if the XPath query fails because the attribute being queried did not exist for the given element.



  def map_pattr(node, fieldx, valuex)

    begin

    parameter = node.root.elements["parameter[@field='#{fieldx}']"]

    parameter.add_attribute('value', valuex)

    parameter

    

    rescue

      puts 'feedpopulated.rb: map_attr() the field ' + fieldx + ' was not found in params.'

      raise

    end

  end

Notice that a raise statement is used to ensure that the system error message is raised and any further code execution is halted.

Without adding a customized helpful message I would be left scratching my head trying to work out what the following system error message meant.



./feedpopulated.rb:27:in `map_pattr': undefined method `add_attribute' for nil:NilClass (NoMethodError)

     from ./feedpopulated.rb:51:in `create_record'

     from ./feedpopulated.rb:49:in `each'

     from ./feedpopulated.rb:49:in `create_record'

     from ./recordx.rb:91:in `call_create'

     from ./s3fileuploader_handler.rb:14:in `call'

     from ./s3fileuploader_handler.rb:40:in `invoke'

     from ./uploadtwitteraudio.rb:22:in `initialize'

     from /usr/lib/ruby/1.8/rexml/element.rb:890:in `each'

     from /usr/lib/ruby/1.8/rexml/xpath.rb:53:in `each'

     from /usr/lib/ruby/1.8/rexml/element.rb:890:in `each'

     from ./uploadtwitteraudio.rb:18:in `initialize'

     from ./uploadtwitteraudio.rb:72:in `new'

     from ./uploadtwitteraudio.rb:72

Reference: Programming Ruby: The Pragmatic Programmer's Guide - Exceptions, Catch, and Throw [ruby-doc.org]

Count the no of elements in an XML node

jrobertson (James Robertson) — Wed, 02 Jan 2008 00:32:42 GMT

This Ruby code count the no. of elements in an xml node by converting the children into an array and then returning the length.



require 'rexml/document'

include REXML



file = File.new('test.xml')

doc = Document.new(file)

puts doc.root.elements.to_a.length

getElementsAt //JavaScript Function

jonasraoni (Jonas Raoni Soares Silva) — Tue, 14 Feb 2006 16:20:27 GMT

This function is able to get all the elements in a specific level of the array

example:



x = [-1, [[8, 22, -7], 32, [[4, 10, -2], 122]], 13];

alert(x.getElementsAt(3));

code:



//+ Jonas Raoni Soares Silva

//@ http://jsfromhell.com

Array.prototype.getElementsAt = function(level){

	var r = [], x = [], c = this, l = level, i;

	do

		if(i = c.length, !l)

			for(; i; r[r.length] = c[--i]);

		else

			for(; i; c[--i] instanceof Array && x.push(c[i], l - 1));

	while(l = x.pop(), (c = x.pop()) != undefined);

	return r;

}