Data migrations can manage the modification of data. It‘s a solution to the common problem of modifying data between code revisions within a document oriented database.

Example of simple migration for a system dependency:

  class AddBaselineSurveySchema < Mongoid::Migration
    def self.up
      SurveySchema.create(:label => 'Baseline Survey')
    end

    def self.down
      SurveySchema.where(:label => 'Baseline Survey').first.destroy
    end
  end

Timestamped Migrations

By default, Rails generates migrations that look like:

   20080717013526_your_migration_name.rb

The prefix is a generation timestamp (in UTC).

If you‘d prefer to use numeric prefixes, you can turn timestamped migrations off by setting:

   Mongoid.config.timestamped_migrations = false

In environment.rb.