Rake Tasks,

database_helpers.txt

http://jacopretorius.net/2014/02/all-rails-db-rake-tasks-and-what-they-do.html
http://guides.rubyonrails.org/active_record_basics.html

# many to many
class CreateEmployeesProjects < ActiveRecord::Migration
  def change

      create_table(:employees_projects) , id: false do |t|
          t.column(:employee_id, :integer)
          t.column(:project_id, :integer)
      end
  end
end

# add index

class AddIndexToEmployeesName < ActiveRecord::Migration
  def change
      add_index :employees, :lastname
  end
end

# adding column
class AddBudgetToProjects < ActiveRecord::Migration
  def change
      add_column(:projects, :budget, :money)
  end
end