Migrer

Migrer (me-gray) is French for migrate. My wife suggested the name, and it was much less obnoxious than morphin_time or flying_v, say. - @sfsekaran

Migrer creates migration-like tasks for running application scripts. It is primarily useful for updating database records or running one-time tasks against separate environments.

What is the difference between this and ActiveRecord migrations?

Migrations should always be stable and are primarily for altering the structure of a database. Migrer is intended for data migrations, or manipulating the data within that structure. Such tasks can become error-prone since they depend on the state of models in the codebase, and are best not included in ActiveRecord migrations.

Why not just create a regular rake task or use a script runner?

Although Migrer data migrations can be run multiple times, they are primarily suited for one-time tasks (and often for tasks that are not intended to be run more than once). Migrer not only creates a structure for these one-time tasks, but also keeps track of which data migrations have already been processed. This is especially useful when managing such tasks among multiple environments.

Add this line to your application's Gemfile:

gem 'migrer'

And then execute:

$ bundle

Or install it yourself as:

$ gem install migrer

And install database migrations like so:

$ bundle exec rake railties:install:migrations FROM=migrer
$ bundle exec rake db:migrate

Migrer can be configured (e.g. in an initializer) as follows:

Migrer.configure do |config|
  config.paranoid = true
end

Configuration options:

paranoid (default: false) - If set to true, a prompt will be required before running each data migration.

Create a data migration:

$ bundle exec rails generate data_migration MyFirstDataMigration "optional description"

This will create the file: db/data_migrate/<timestamp>_my_first_data_migration.rb

Open this file and replace "TODO" with your data migration code!

Unless you have the RAILS_ENV environment variable already set, prepend this to all of the following commands (replace <environment> with the correct Rails environment (development, staging, production, etc.):

RAILS_ENV=<environment>

NOTE: If the 'paranoid' configuration variable is set to true, or if the commands are run with the PARANOID=true environment variable, all the following commands will ask for confirmation before executing.

Run all unprocessed data migrations:

bundle exec rake data:migrate

Run a single data migration (<version> is the timestamp at the beginning of the data migration file, just like ActiveRecord migrations):

bundle exec rake data:migration VERSION=<version>

Mark all data migrations as already processed:

bundle exec rake data:mark_all

Mark a single data migration as already processed:

bundle exec rake data:mark VERSION=<version>

Mark all data migrations as unprocessed (so they are included again when running data:migrate):

bundle exec rake data:unmark_all

Mark a single data migration as unprocessed:

bundle exec rake data:unmark VERSION=<version>

View all unprocessed data migrations by filename:

bundle exec rake data:pending

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

• Sathya Sekaran (sfsekaran)
• Michael Durnhofer (mdurn)