Flowdock
method

reversible

Importance_2
v4.0.2 - Show latest stable - 0 notes - Class: ActiveRecord::Migration
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reversible() public

Used to specify an operation that can be run in one direction or another. Call the methods up and down of the yielded object to run a block only in one given direction. The whole block will be called in the right order within the migration.

In the following example, the looping on users will always be done when the three columns ‘first_name’, ‘last_name’ and ‘full_name’ exist, even when migrating down:

class SplitNameMigration < ActiveRecord::Migration
  def change
    add_column :users, :first_name, :string
    add_column :users, :last_name, :string

    reversible do |dir|
      User.reset_column_information
      User.all.each do |u|
        dir.up   { u.first_name, u.last_name = u.full_name.split(' ') }
        dir.down { u.full_name = "#{u.first_name} #{u.last_name}" }
        u.save
      end
    end

    revert { add_column :users, :full_name, :string }
  end
end
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