Posts Tagged ‘rails’

exception iteration in ruby

January 29th, 2010 Comments off

There are many ways to iterate in ruby, many methods, but going back to assembler roots of mine I found another one:

>> a=[1,2,3]
=> [1, 2, 3]
>> begin puts a.shift; raise unless a.blank?; rescue; retry; end
=> nil

This code is only prof of concept, it should not be used for iterations, by example if it would be used without prior initialization of “a” variable it would be an endless loop as on exception “NameError” it will retry in endless loop.

There are other places where this could be used, but even possible retry should not be used without some kind of endless loop protection like:

>> i=10; begin puts'some.file'); rescue; if i>0 then puts "#{i} ..."; i-=3; sleep 1; retry; end; end
10 ...
9 ...
8 ...
7 ...
some file created
=> nil

In this example a file was created during run of the command – on second console by just running “echo some file created > some.file”.

There are other ways to do the same, maybe not so cool like that above but probably most of developers will prefer something like:

>> 10.downto(1){|i| begin puts'some.file'); break; rescue; puts "#{i} ..."; sleep 3; end }
10 ...
9 ...
8 ...
some file created
=> nil

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Categories: Development Tags: , , ,

string to class in ruby on rails

January 26th, 2010 Comments off

There are few ways to have a class from a string, most know are:

  • Kernel.const_get(‘User’)
  • eval(‘User’)
  • ‘User’.constantize

The order in which I have named them is important – a bit important, Kernel.const_get is 10 times faster then constantize and 5 times faster then eval.

The reason of such speed for Kernel.const_get is from it has to maintain list of all constants in the application, tests show it may even behave faster then storing names and Class mapping in a hash.

The difference is not big on simple calls to create just one or two classes, but on heavy loaded systems this might give some more percents of the hardware.

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Rails auto_complete nested list

June 9th, 2009 1 comment

Yesterday I was implementing auto completion for categories. The idea was to get possibility to write by hand categories but keep them as has_many_through association in database.

After six hours of coding I got this working – that is why I’m against rails, with such big amount of plugins, gems and blogs you have to spent a lot of time to do small things.

This code works with rails 2.3

So first we have to install auto_complete plugin which was quite handy:

script/plugin install auto_complete
script/plugin discover

Second we need to define migration:

  create_table :book_categories do |t|
    t.references :books
    t.references :categories
  create_table :books do |t|
    t.string :title
  create_table :categories do |t|
    t.string :name

At third step we define models:

class Book < ActiveRecord::Base
  has_many :book_categories, :dependent => :destroy
  has_many :categories, :through => :book_categories
class BookCategory < ActiveRecord::Base
  belongs_to :book
  belongs_to :category
class Category < ActiveRecord::Base
  has_many :book_categories, :dependent => :destroy
  has_many :books, :through => :book_categories

Time for forth step – faking Book properties:

class Book < ActiveRecord::Base
has_many :book_categories, :dependent => :destroy
has_many :categories, :through => :book_categories
def categories_list{|c|}*”, ”

def categories_list=(list)
list_names = list.split(‘,’).map{ |e| e.strip }.uniq
list_existings = Category.find(:all, :conditions => [ ‘name IN (?)’, list_names ], :select => ‘id,name’ )
list_existings_names = { |e| }
list_add = list_names-list_existings_names
list_new = { |e| }
list_old = { |e| }.uniq
list_add.each do |name|
self.categories << => name)
self.categories << Category.find(:all, :conditions => [ ‘id IN (?)’, list_new-list_old ], :select => ‘id’ )
self.categories.delete Category.find(:all, :conditions => [ ‘id IN (?)’, list_old-list_new ], :select => ‘id’ )

Now we can have some rest from coding and play a bit with new models using “script/console”:

>> => 'a').save
>> => 'b').save
>> => 'c').save
>>{|c| [,] }
=> [[1, "a"], [2. "b"], [3, "c"]]
>> b =>'some book')
>> b.categories_list='a,b,c'
>> b.categories
=> [#<Category id: 1>, #<Category id: 2>, #<Category id: 3>]
>> b.categories_list='a,c,d'
>> b.categories
=> [#<Category id: 1>, #<Category id: 3>, #<Category id: nil, name: "d">]
>>{|c| [,] }
=> [[1, "a"], [2. "b"], [3, "c"], [4, "d"]]

Fifth step is to write edit/new view:

<% form_for(@book) do |f| %>
    <%= f.label :title, t(:book_label_title) %><br />
    <%= f.text_field :title %>
    <%= f.label :categories_list, t(:book_label_category) %><br />
    <%= text_field_with_auto_complete :book, :categories_list, {}, { :method => :get } %>
<% end %>

Six step is to define action in controller:

class BooksController < ApplicationController
  def auto_complete_for_book_categories_list
    list = params['book']['categories_list'].split(',').map{ |e| e.strip }

    name = list.pop

    find_options = {
      :conditions => [ "name LIKE ?", '%' + name + '%' ],
      :order => "name ASC",
      :limit => 10,
      :select => 'id, name',

    @items = Category.find(:all, find_options).select { |e| !list.include?( }.
      map { |e| list.push(;*', '); list.pop(); e }

    render :inline => "<%= auto_complete_result @items, 'name' %>"
  #other actions go here ...

The seventh and last step is to add routing:

map.resources :books, :collection => { :auto_complete_for_book_categories_list => :get }

Hope that this will help someone.

Categories: Development Tags: , ,

easy capistrano remote invocation

May 6th, 2009 Comments off

Today I was coding just for fun … and wrote my own Capistrano script for deployment, during this I have found great way to invoke remote tasks.

The method is easy, add following code to your config/deploy.rb file:

set :sudo_call, ''
desc 'makes remote/rake calls to be executed with sudo'
task :use_sudo do
  set :sudo_call, 'sudo'

desc 'run rake task'
task :rake do
  ARGV.values_at('rake')+1,-1)).each do |task|
    run "cd #{current_path}; #{sudo_call} RAILS_ENV=production rake #{task}"

desc 'run remote command'
task :remote do
  run "cd #{current_path}; #{sudo_call} RAILS_ENV=production #{command*' '}"

desc 'run specified rails code on server'
task :runner do
  run "cd #{current_path}; RAILS_ENV=production script/runner '#{command*' '}'"

Now try your new tool with following commands:

cap rake db:migrate
cap use_sudo rake db:migrate
cap remote "tail -n 10 log/production.log"
cap use_sudo remote cat /etc/passwd
cap runner p User.all
cap runner "User.all.each{ |u| p u }"

In the third call I have used parentheses to hide “-n” form Capistrano, because it is its parameter, to see whole list of Capistrano parameters call it with “cap –help”. For the last command I have used parentheses again because now it contained bash special characters.

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Categories: Development, Linux Tags: , , , ,

Ruby on Rails application in 10 minutes is a myth

April 2nd, 2009 5 comments

Lately netbeans remainded me about something that makes great marketing for Ruby on Rails – ability to create application in 10 minutes.

By example you can have a look on the netbeans tutorial. Everything looks great, sometimes You can even create the application in 10 minutes …

Lets think what You will get in this 10 minutes:

  • Scaffold of application … without head or legs

Thats all, the application generated in 10 minutes does not have authentication, it does not have administrative part. Of course there is a lot of plugins, that helps to add functionality to Yours application. But wait a minute, authors of this plugins cant catch up stable rails.

Each few months we have new rails version, and each version is requiring application changes, this is endless. After You finish migration to newest rails, after You find new plugins there is new rails version – and the  wheel spins again.

Comparing to other applications rails is getting new releases at least twice offten, that would be good if it would have one stable base, but not, the base is changing each few months.

And what is the plan, four months after rails 2.3 we will have rails 3.0, it will be more like rails or maybe more like merb? Hopefully it will start slowing down a bit, as it requires now very big efforts to maintain application and keep it up todate.

Somebody would say “You can freeze rails, gems and plugins” – yes I can, but I can not freeze my developers, they will learn new rails version, and after one year I will have a team of experienced developers in rails 4.0 or even rails 5.0 and application with frozen reail 2.3 … and try to migrate when the core was rewritten three times during last year.

Assuming having steady framewoirk with “broken tables” like Java or less broken DJango makes a lot more work on begining, but development stacks are available, the documentation is more complete, and the major version changes once for few years, this allows developer to understand and modify application code even after ten years.

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Categories: Development Tags: , ,