reversible()
Instance Public methods
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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