Welcome Monsoon !

The monsoon has started in Mumbai - Maharashtra with full force and one of my friends forwarded some great nature pictures especially from Konkan region to me. I can not resist myself to share some of those beautiful photos with you all.

Marleshwar waterfall near Sangameshwar in Ratnagiri district:



Jog waterfall:



A typical home in Konkan:



River bank:




Happy monsoon ! :-)
It's real time to go for a trek / nature trail !

hash_key_as_attribute gem published

Following my earlier post, I pushed hash_key_as_attribute gem to rubygems.org

Install
====
gem install hash_key_as_attribute

OR

Download the gem file from http://github.com/NiranjanSarade/hash_key_as_attribute/
gem install hash_key_as_attribute-0.0.1.gem

Allowing hash values to be set and retrieved as if they were attributes

In ruby, we have OpenStruct which allows the creation of data objects with arbitrary attributes. With ruby's metaprogramming capability, we can also allow hash values to be set and retrieved as if they were its attributes. If the key does not correspond to any hash entry, it should return “The key does not correspond to any hash entry” message. The hook that we are going to use is Kernel's method_missing.

Here we are opening the class Hash :-



And this is the sample output :-

h = Hash.new("The key does not correspond to any hash entry")
h.one = 1
puts h.one #=> 1

h.two= [1,2,3,4]
puts h.two.inspect #=> [1,2,3,4]

puts h.three #=> "The key does not correspond to any hash entry"

puts h.inspect #=> {:one=>1, :two=>[1, 2, 3, 4]}

h2 = {}
h2.four = 4

h.three = h2

puts h.three.inspect #=> {:four=>4}

puts h.three.four #=> 4

Instance and class variable get set methods

In ruby, instance variables have prefix '@' and class variables have prefix '@@'.

We have instance_variable_get and instance_variable_set methods from Object class and class_variable_get and class_variable_set methods from Module class in Ruby. Here is the typical usage of these methods from the ruby docs :-

----
class Fred
@@foo = 99
end

def Fred.foo
class_variable_get(:@@foo) #=> 99
end

----
class Fred
def initialize(p1, p2)
@a, @b = p1, p2
end
end
fred = Fred.new('cat', 99)
fred.instance_variable_get(:@a) #=> "cat"
fred.instance_variable_get("@b") #=> 99

----
class Fred
def initialize(p1, p2)
@a, @b = p1, p2
end
end
fred = Fred.new('cat', 99)
fred.instance_variable_set(:@a, 'dog') #=> "dog"
fred.instance_variable_set(:@c, 'cat') #=> "cat"
fred.inspect #=> #Fred:0x401b3da8 @a=\"dog\", @b=99, @c=\"cat\"
----

However, why do we need to specify the @ and @@ when the method names are smart enough to distinguish between whether the variable is an instance or a class variable. Why does a call to instance_variable_set require the "@" symbol in the first argument? Any idea ? Or has it been done with some purpose ?

Do you want to touch real Tigers ?

Last week my wife and I visited Thailand. In the tour, we got a chance to visit Tiger Temple near Bangkok. Yes ... the thrill was patting real tigers. Tiger Temple, or Wat Pha Luang Ta Bua, is a Buddhist temple in Western Thailand where tourists can actually touch/pat the tigers in open area. It was a great experience in watching the real tigers staying with men and how the people take care of them. The tigers are handled by Thai monks, volunteers and the local staff.

Sharing few photos ...

Ruby metaprogramming

This is an excellent video about ruby metaprogramming concept:-
http://www.infoq.com/presentations/metaprogramming-ruby

This was presented by Dave Thomas, a well known author of The Pragmatic Programmer book.

Passing hash from javascript

I was working on one functionality where I needed to build hash like structure in javascript and make an ajax call to perform that particular action by passing that hash as params to process further. The functionality was to delete a numbered row from the form and after deletion the form should rearrange the rows in sequence while maintaining the order. I used javascript 2 dimensional array to treat it as hash.

e.g. On the form :-

No. | EmpID | Date | Location | Action |
1. | 123 |12-Mar-10 | Mumbai |Delete |
2. | 233 |10-Jan-10 | Mumbai |Delete |
3. | 444 |15-Mar-10 | Mumbai |Delete |
4. | 555 |18-Mar-10 | Mumbai |Delete |

So. If you delete the 3rd row, then after deletion the new form should render as :-

No. | EmpID | Date | Location | Action |
1. | 123 |12-Mar-10 | Mumbai |Delete |
2. | 233 |10-Jan-10 | Mumbai |Delete |
3. | 555 |18-Mar-10 | Mumbai |Delete |

The elements were written in table format. Each row is assigned unique id, so first row will have id = 1, 2nd row with id = 2 and so on. Each td has unique class.

<%=row_id%>
<%= text_field_tag "emp_#{row_id}", "", :id => emp_#{row_id}" %>
<%=text_field_tag "dt_#{row_id}", "", :id => "dt_#{row_id}" %>
<%= text_field_tag "loc_#{row_id}", "", :id => "loc_#{row_id}", %>
<%=link_to(image_tag("delete_img.jpg", :alt => "Delete Row", :id => "del_#{row_id}"),"#")%>

This is the jquery code :-

jQuery(document).ready(function() {
jQuery('#del_<%=i%>').click(function() {
var row_to_be_deleted = jQuery(this).parent().parent().parent();
var row_id = parseInt(row_to_be_deleted.attr("id"));
var data_ary = [];

jQuery('#emp_table tbody > tr').each(function() {
if (jQuery(this).attr("id") != row_id) {
var myArray = [];
var empid_val = "";
var dt_val = "";
var loc_val = "";
jQuery(this).find("td").each(function(){
if (jQuery(this).attr("class")== "empid"){
empid_val = jQuery(this).find("input").val();
myArray.push(empid_val);
}
if (jQuery(this).attr("class")== "dt"){
dt_val = jQuery(this).find("input").val();
myArray.push(dt_val);
}
if (jQuery(this).attr("class")== "loc"){
loc_val = jQuery(this).find("input").val();
myArray.push(loc_val);
}
});
data_ary.push(myArray);
}
});
ajax_call_for_remove_row( data_ary, '<%= remove_row_controllername_url%>');
});
});
----
function ajax_call_for_remove_row(data_ary, remove_row_url) {
var inputs = new Object;
inputs["data_ary"] = data_ary;
jQuery.ajax({
url: remove_row_url,
data: inputs,
error: function (XMLHttpRequest, textStatus, errorThrown) {
alert("We are sorry something went wrong, please try again");
},
success: function(data){
},
type: "post"
});
}
----
The corresponding controller actions :-

def remove_row
@data = []
logger.debug(params['data_ary'].inspect)
build_data_from_hash(params['data_ary'])
logger.debug(@data.inspect)
end

private

def build_data_from_hash data_hash
if data_hash
data_ary = sort_hash_to_array data_hash
data_ary.each { |value|
@data << {"Empid" => value[1][0], "Date" => value[1][1], "Location" => value[1][2] }
}
else
@data << {"Empid" => "", "Date" => "", "Location" => "" }
end
end

def sort_hash_to_array data_hash
data_hash.sort { |a,b| a[0].to_i <=> b[0].to_i }
end
----

params['data_ary'].inspect =>
====================================
{"0"=>["123", "12-Mar-10", "Mumbai"], "1"=>["233", "10-Jan-10", "Mumbai"], "2"=>["555", "18-Mar-10", "Mumbai"]}
====================================

@data.inspect =>
====================================
[["0", ["123", "12-Mar-10", "Mumbai"]], ["1", ["233", "10-Jan-10", "Mumbai"]], ["2", ["555", "18-Mar-10", "Mumbai"]] ]
====================================

We can pass this @data as local while rendering the table body partial in corresponding js.erb template. This works great for me!

RubyConf 2010 - Bangalore, India

In the last month, I got an opportunity to attend the very first Ruby conference held in Bangalore, India(20-21 March) organized by ThoughtWorks. The response was very huge (around 400 people ranging from beginners to CEOs from more than 100 companies) and people really enjoyed the event.

It was really great to hear some good speakers/industry leaders like Matz, Obie Fernandez, Ola Bini, etc. Many technical topics were presented like future of Ruby, Rails 3.0, Glassfish and WebRoar app servers, building cross platform mobile application with Rhodes framework, etc. You can find more details about these topics at http://rubyconfindia.org/

I felt a lot of enthusiasm and energy amongst the people w.r.t. Ruby and Rails. There are many small companies being set up especially in Pune and Bangalore for doing only rails projects. I really liked that !

Indian market is really catching up on Rails very fast !

Rendering partial with jquery

Below is the way by which you can render partial with jQuery in your view.js.erb file :-

jQuery("#mydiv").html("<%= escape_javascript(render(:partial => 'my_partial', :locals => {:my_instance_var => @my_instance_var} ))%>");

A mechanic and a surgeon

A mechanic was removing a cylinder head from the motor of a Harley motorcycle when he spotted a well-known heart surgeon in his shop. The surgeon was there, waiting for the service manager to come and take a look at his bike. The mechanic shouted across the garage, "Hey, Doc, can I ask you a question?"

The surgeon a bit surprised, walked over to the mechanic working on the motorcycle. The mechanic straightened up, wiped his hands on a rag and asked, "So Doc, look at this engine. I open its heart, take valves out, fix 'em, put 'em back in, and when I finish, it works just like new. So how come I get such a small salary and you get the really big bucks, when you and I are doing basically the same work?"

The surgeon paused, smiled and leaned over, and whispered to the mechanic...
"Try doing it with the engine running."