rails string to boolean migration while preserving existing data

gistfile1.rb

class ChangeIgnoredToBoolean < ActiveRecord::Migration
  # we should have been using boolean vs string for a flag instead of a string
  def up
    # preserve existing data
    @saved_ignored_state = Message.all.map(&:ignored)
    change_column(:messages, :ignored, :boolean, :default => false)
    Message.reset_column_information
    Message.all.each_with_index do |message,index|
      message.update_attribute(:ignored,@saved_ignored_state[index] == 'true')
    end
  end

  def down
    # preserve existing data
    @saved_ignored_state = Message.all.map(&:ignored)
    change_column(:messages, :ignored, :string, :default => 'false')
    Message.reset_column_information
    Message.all.each_with_index do |message,index|
      message.update_attribute(:ignored,@saved_ignored_state[index] == true ? 'true' : 'false')
    end
  end
  
end

Hey, thanks, this was really useful!

Alternative way

class ChangeIgnoredToBoolean < ActiveRecord::Migration
  def self.up
    execute "ALTER TABLE messages ALTER COLUMN ignored DROP DEFAULT"
    change_column :messages, :ignored, "boolean USING ignored != 'false'"
    change_column_default :messages, :ignored, false
  end

  def self.down
    execute "ALTER TABLE messages ALTER COLUMN ignored DROP DEFAULT"
    change_column :messages, :taxation, "varchar(255) using case when ignored then 'true' else 'false' end"
    change_column_default :messages, :ignored, 'false'
  end
end