Veerasundaravel's Ruby on Rails Weblog

November 26, 2014

Rails find_each method with order option

Filed under: Rails3, Ruby, Ruby On Rails — Tags: , , , , , , , — Veerasundaravel @ 9:36 pm
Rails find_each or find_in_batches methods are looping through a collection of records from the database.
This batch processing methods allow us to work with the records in batches, thereby greatly reducing memory consumption.
Person.find_each(:conditions => "age > 21") do |person|
  person.party_all_night!
end
But major drawback with these methods is  - ordering/sorting the records by primary key id, hence we cannot specify our own order_by.
order_by(:created_at).find_each == FAIL!!!
class ActiveRecord::Base
  # normal find_each does not use given order but uses id asc
  def self.find_each_with_order(options={})
    raise "offset is not yet supported" if options[:offset]

    page = 1
    limit = options[:limit] || 1000

    loop do
      offset = (page-1) * limit
      batch = find(:all, options.merge(:limit=>limit, :offset=>offset))
      page += 1

      batch.each{|x| yield x }

      break if batch.size < limit
    end
  end
end

July 2, 2014

Rails – Force update ActiveRecord updated_at column

Filed under: Ruby On Rails — Tags: , , , , , , — Veerasundaravel @ 12:11 am

When we usually modify any specific column/field in our model, Active-record will check whether the corresponding value is new or not.

If it is new then only it will create a DB query and update that value with current timestamp in updated_at column, if there is no change in existing value means it will only fire commit query only. There wont be any change in updated_at column.

So if we want modify the timestamp of updated_at field without updating any field means, we can follow any of below two methods:

Method 1:
user.update_attributes(:name => “same old name”, :updated_at => Time.now)

Method 2:
user.touch

Both of above two methods will modify updated_at value with current timestamps even if there is any change in other fields or not.

 

January 28, 2013

Kill a program using Ruby

Filed under: Ruby, Ruby On Rails — Veerasundaravel @ 12:54 pm

Old school but helpful.

Get process id of a running program and kill it if you need.

pid = `pgrep -f “ruby running_program.rb”`.split(“\n”).first.to_i
`kill -9 #{pid}`

Specify your program or script name inside the double quotes instead of ruby running_program.rb. It will return the pid of the program and you can get it in the variable pid. In next line you can see the kill command in order to kill the program.

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