From Java To Ruby

Hpricot for XML parsing

2008-11-09T18:07:00.000-08:00

Hpricot is flexible and fast html/xml parser.
To install:
$ sudo gem install hpricot

require 'hpricot'

doc = Hpricot(xml_string)
doc.search("/rows/row").each do |row|
group_and_row_id = row.get_attribute("id")
row.search("/cell").each do |cell|
cell_text = cell.html
end
end

Caution with String concat <<

2008-11-09T17:54:00.000-08:00

If you have a string a = "test" and you want to append dynamic data, be careful with <If the dynamic data happens to be a Fixnum between 0 and 255, it is converted to a character before concatenation.

>> a = "test"
=> "test"
>> a << 12
=> "test\f"
>>

dhtmlxGrid in a Rails App

2008-11-09T17:41:00.000-08:00

Here is my experience using dhtmlxGrid in ROR app.
In general, it is a nice component and comes with lots of sample code. Their support and knowledge is good. Their document list json as supported data type but json support is a subset of XML type. Even if you load the grind in JSON, when you serialize the grid, you get xml back and cell id is not sent back. In rails project, to generate xml, when you use xml builder, make sure, you don't indent. Grid dosn't load xml string with indentation.
Use Builder::XmlMarkup.new (no indent)

Don't use column name type

2008-11-09T17:34:00.000-08:00

I had a table and there was a business need to add a type column in the table. Adding a type column as an integer or as an string didn't work.
"type" is a reserved field name for single table inheritance (STI). Active Record allows inheritance by storing the name of the class in a column that by default is called “type”

Here are the magic field names in Rails:
http://wiki.rubyonrails.com/rails/pages/MagicFieldNames

HowtoGenerateJSON

2008-11-09T17:09:00.000-08:00

Recently, I needed JSON format to load data in dhtml component. It was trivial. I installed ruby-json gem. In my model class, I had to do the following:

require 'json/objects'

def to_json
result = Hash.new
rows = []
qg_rows = all_records

qg_rows.each_with_index do |row_data|
row = {}
data = []
row_data.each {|cells|
------
data << cell_data
}
row [:data] = data
rows << row
end
result[:rows] = rows
result.to_json

end

escaping javascript

2008-10-11T10:40:00.000-07:00

Javascript provides

escape(string)

method but it does not escapes the following chars:
* @ - _ + . /

Use encodeURIComponent(URIstring)instead. The encodeURIComponent method encodes all characters.

Use the decodeURIComponent() function to decode URIs encoded with encodeURIComponent().

URI escaping

2008-10-10T05:47:00.000-07:00

Which one to use? URI.escape or CGI.escape? Lets look at irb:
>> URI.escape('Test <>?/&;=:.')
=> "Test%20%3C%3E?/&;=:."
>> CGI.escape('Test <>?/&;=:.')
=> "Test+%3C%3E%3F%2F%26%3B%3D%3A."

CGI.escape is looking better but it does not escape dots which gives "RoutingError No route matches". Here is the solution working for me
>> test = URI.escape(CGI.escape('Test <>?/&;=:.'),'.')
=> "Test+%3C%3E%3F%2F%26%3B%3D%3A%2E"
>> CGI.unescape(test)
=> "Test <>?/&;=:."

Formatting phone numbers, Fax numbers

2008-10-05T17:08:00.000-07:00

I created a plug-in act_as_formatted to format numbers, phone/fax numbers and zip codes. If there is number field (stored as integer in DB) and user formats it using "," for example 10,010, this gets saved as 10 (without special handling). To solve this problem I created a plug-in act_as_formatted. This plug-in creates *_ui and *_ui= methods on ActiveRecord models. attrubute_ui does the formatting and attribute_ui= ensures, right data is being saved. Example usage:
In model
acts_as_number :revenue
acts_phone_number :phone
In view use attribute_ui
<%= company.revenue_ui %>
<%= company.phone_ui %>
---------------------------------------
Here is the code. Ideally model should not be using ActionView::Helpers::NumberHelper but for now this seems to be working fine for e.

class ActiveRecord::Base
include ActionView::Helpers::NumberHelper
include ERB::Util

def self.format_as_number(*args)

args.each do |arg|

define_method "#{arg.to_s}_ui=" do |number_string|
if number_string
# If a valid number, sanitize to digits only
if valid_number? number_string
number_string.gsub!(/[^0-9]/, "")
end
end
write_attribute(arg, number_string)
end
end

args.each do |arg|
define_method "#{arg.to_s}_ui" do
val = read_attribute(arg)
begin
number_with_delimiter val if val
rescue
val
end
end
end

define_method 'validate' do
args.each { |arg|
error_message = 'is invalid. It can contain only digits'
if !eval(arg.to_s).nil?
errors.add(arg, error_message) unless valid_number? eval(arg.to_s)
end
}
end
end

def self.format_as_phone_number(*args)

args.each do |arg|

define_method "#{arg.to_s}=" do |number_string|
if number_string
# If a valid phone number(can contain only 0-9/-()+xX),
# sanitize it to "digits only" only if 10 digits long
# If number has more that 10 digits, store it as is
if valid_phone? number_string
numbers = number_string.gsub(/[^0-9]/, "")
if numbers.size == 10
number_string = numbers
end
end
end
write_attribute(arg, number_string)
end
end

args.each do |arg|
define_method "#{arg.to_s}_ui" do
val = read_attribute(arg)
begin
if val
numbers = val.gsub(/[^0-9]/, "")
#Format 10 digits phone number only
if numbers.size == 10
return number_to_phone(numbers,:area_code => true)
end
end
val
rescue
val
end
end
end

define_method 'validate' do
args.each { |arg|
error_message = 'is invalid. It must contain at least 5 digits, only the following characters are allowed: 0-9/-()+x'
if !eval(arg.to_s).nil?
errors.add(arg, error_message) unless valid_phone? eval(arg.to_s)
end
}
end
end

# Valid phone number can contain only 0-9/-()+xX and whitespace.
def valid_phone?(number)
return true if( number.nil? || number.strip.size == 0)
n_digits = number.scan(/[0-9]/).size
valid_chars = (number =~ /^[xX.+\/\-() 0-9]+$/)
return n_digits >= 5 && valid_chars
end

# Valid number can contain only digits and ,.
def valid_number?(number)
return true if( number.nil? || number.strip.size == 0)
valid_chars = (number =~ /^[\,\ 0-9]+$/)
return valid_chars
end

end

Protecting app from Cross Site Scripting

2008-10-04T16:44:00.000-07:00

RoR provides methods for escaping metacharacters. To HTML escape data in RoR simply add an "h" inside your output tag.

It is hard to remember using this everywhere.

There are several plug-in available which you can install and forget about adding "h". I tried auto_escape plug-in. This modifies ActiveRecord and and automatically applies CGI.escapeHTML to all text column. The plug-in works by defining an after_find call_back from ActiveRecord. Whenever a record is found and loaded from DB, this escapes text columns. Plug-in worked great but it slowed down the APP.

xss_terminate plug-in makes stripping and sanitizing HTML automatic. Install the plug-in and forget about h() because you don't need to. This plug-in makes use of before_save hook and strips HTML tags. Generally there are more read operations than save, so performance wise this plug-in worked better for my case.

Textfield with auto complete

2008-07-15T17:22:00.000-07:00

I wanted to add auto complete feature in a form field. I used auto_complete plug-in. It is a great plug-in, very simple to use. In few lines of code, I was able to get this up and running.

1) To install run script/plugin install auto_complete
2) In controller, add auto_complete_for :tag, :name where Tag is a model and name is a field, I wanted my auto complete on.
3) In view add <%= text_field_with_auto_complete :tag, :name %>. The method it implements will search through all the Tags in you records database and do a LIKE comparison on the name column, comparing the name to the contents of the tag[title] form field.
4) I had to reopen auto_plug to fix "Mysql::Error: #23000Column 'name' in where clause is ambiguous". In my case, for auto_complete_for method I was passing :joins condition.
I wanted to show tags for a given model. Both Tag and Model had same column name "name". To fix the problem, I created another plug_in name auto_complete_extended with single class init.rb. In init.rb I reopened auto_complete_for method (as follows):

class ActionController::Base
# Reopening auto_complete_for from auto_complete plug-in
### This is copy of auto_complete_for except for the part in condition where it qualifies column name with table name.

def self.auto_complete_for(object, method, options = {})
define_method("auto_complete_for_#{object}_#{method}") do
find_options = {
:conditions => [ "LOWER(#{object.to_s.pluralize}.#{method}) LIKE ?", '%' + params[object][method].downcase + '%' ],
:order => "#{method} ASC",
:limit => 10 }.merge!(options)

@items = object.to_s.camelize.constantize.find(:all, find_options)

render :inline => "<%= auto_complete_result @items, '#{method}' %>"
end
end
end

Thanks to for the following post. It helped me get started. http://codeintensity.blogspot.com/2008/02/auto-complete-text-fields-in-rails-2.html

File upload with attachment_fu

2008-06-23T18:17:00.000-07:00

Attachment_fu is a great plug-in to upload a file. I used Mike Clark's blog as an example. By default, it gives the following validation message:
Content type can’t be blank
Content type is not included in the list
Size can’t be blank
Size is not included in the list
Filename can’t be blank

To get better validation message, either reopen attachment_fu.rb or do your own validation in your model. The following blog explains it nicely.

If you are using MySQL, you may want to increase max_allowed_packet size in “my.cnf”. The default size is apparently 1M. If you don't change this and upload a file larger than 1 M, you will get “ActiveRecord::StatementInvalid: Mysql::Error: #08S01Got a packet bigger than ‘max_allowed_packet’ bytes: INSERT INTO...

WYSIWYG-editor on Rails

2008-06-22T12:45:00.000-07:00

I found the following post very helping http://public.ok2life.com/welcome/index/48 and http://public.ok2life.com/welcome/index/49.html and http://www.fckeditor.net/demo. We are using FCKEditor and so far it is going very smoothly. In order to add a custom toolbar option, you need to write a plugin to fckeditor. In order to make spell checker to work, you need to install aspell http://wiki.lyx.org/Mac/MacSpelling and include file ActionView::Helpers::SanitizeHelper. I added the following line application's initializers dir
include ActionView::Helpers::SanitizeHelper
This was needed in Fckeditor: Version 0.4.3.

To write a plug-in to fckeditor, follow direction on http://docs.fckeditor.net/FCKeditor_2.x/Developers_Guide/Customization/Plug-ins. After reading documentation from this link, I used the following plugin as an example (note: fckeditor comes with this plug-in): /fckeditor/public/javascripts/fckeditor/editor/plugins/placeholder/

Graph/Charts

2008-06-22T12:25:00.000-07:00

For charts on rails, I looked GRUFF and OpenFlash. Open flash is very easy to use and provides more configuration options. You can get more information on open_flash_chart plug-in from the following http://teethgrinder.co.uk/open-flash-chart . I had to reopen Graph from open_flash_chart library, and redefine some methods to make look and feel changes.
Sample:

#Redefining method pie(alpha, line_color, style, gradient = true, border_size = false)
# Original method had bug where it won't let you drop gradient
def pie(alpha, line_color, style, gradient = true, border_size = false)
@pie = "#{alpha},#{line_color},#{style}"
if !gradient
#@pie += ",#{!gradient}" # This is bug and won't drop gradient color
@pie += ",#{gradient}"
end
if border_size
@pie += "," if gradient === false
@pie += ",#{border_size}"
end
end

# Original Graph class is not exposing grid color setters.
def set_grid_color( color = '')
@x_grid_color = color
@y_axis_color = color
@x_axis_color = color
@x_grid_color = color
@y_grid_color = color
end

Ruby/Rails IDE

2008-06-22T11:00:00.000-07:00

TextMate is the editor of choice for most folks on Mac but I am from Java and Windows. I missed rich IDE like features in TextMate. Most of all I missed nice debugging support. I evaluated Netbeans(6.1 RC2) and Aptana Studio(Eclipse based: build: 1.1.6.009905). I liked Aptana. Netbeans had very basic debugging support. Aptana debugging is richer. I tried using TextMate for a week too. In my opinion, if you are comfortable with Eclipse IDE, and if you use Aptana, you are not missing any thing big from TextMate. Here are more resources:
http://aptana.com/rails
http://tnlessone.wordpress.com/2007/02/28/ruby-rails-ide-comparison-idea-netbeans-radrails/

Books needed to get you started

2008-06-22T10:35:00.000-07:00

Ruby for Rails: Ruby Techniques for Rails Developers by David Black is the best beginner book for learning ruby. This book gives you very good base on Ruby. I tried reading Programming Ruby: The Pragmatic Programmer's Guide as 1st book but it didn't go that well. After reading Ruby for Rails, I read Agile Web Development with Rails, 3rd Edition. This will get you started with Ruby and Rails. The Ruby Way and The Rails Way are good reference books .