niczsoft

I have seen a lot of migrations, most of them was just doing what it had to do. But I found a nice way to make my migrations more pretty.

So I had an Article model, which had field :published of type :boolean , as comparing to other solutions, I found that it should be rather :publish_date of type date.
First I have created migration using “script/generate migration article_update” and got empty migration:

class UpdateArticles < ActiveRecord::Migration
  def self.up
  end
  def self.down
  end
end
&#91;/sourcecode&#93;
To be able to freely play with Fields we add our private implementation of article model, we change the fields and move data for them:
&#91;sourcecode language='ruby'&#93;
class UpdateArticles < ActiveRecord::Migration
  class Article < ActiveRecord::Base; end
  def self.up
    add_column :articles, :publish_date, :datetime, :null => true
    Article.reset_column_information
    Article.all.each { |article| article.update_attribute(:publish_date, :created_at) if article.publish }
    remove_column  :articles, :publish
  end
  def self.down
    add_column  :articles, :publish, :boolean
    Article.reset_column_information
    Article.all.each { |article| article.update_attribute(:publish, true) unless article.publish_date.nil? }
    remove_column :articles, :publish_date
  end
end

But this is not really what we wanted, if we have already a lot of data in Article tables then we will not know what is going on during update attribute action.
To make it display pretty we have to add say_with_time function:

class UpdateArticles < ActiveRecord::Migration
  class Article < ActiveRecord::Base; end

  def self.up
    add_column :articles, :publish_date, :datetime, :null => true
    say_with_time "Updating publish_date column" do
      Article.reset_column_information
      Article.all.each { |article| article.update_attribute(:publish_date, :created_at) if article.publish }
    end
    remove_column  :articles, :publish
  end

  def self.down
    add_column  :articles, :publish, :boolean
    say_with_time "Updating publish column" do
      Article.reset_column_information
      Article.all.each { |article| article.update_attribute(:publish, true) unless article.publish_date.nil? }
    end
    remove_column :articles, :publish_date
  end
end

And after running migration we will get he following result:

==  UpdateArticles: migrating =================================================
-- add_column(:articles, :publish_date, :datetime, {:null=>true})
-> 0.0007s
-- Updating publish_date column
-> 0.0034s
-- remove_column(:articles, :publish)
-> 0.0224s
==  UpdateArticles: migrated (0.0269s) ========================================

For me it was very small amount of data and the migration went fast, but if i would run it on production with thousands of records then it may take a bit more.

I know this exact code could be rewritten using SQL – and it would be almost always done in seconds, but even then It is nice to show progress, because person responsible for deployment might be confused seeing only blinking cursor.

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