class CreateProjectsTrackers < ActiveRecord::Migration[4.2] def self.up create_table :projects_trackers, :id => false do |t| t.column :project_id, :integer, :default => 0, :null => false t.column :tracker_id, :integer, :default => 0, :null => false end add_index :projects_trackers, :project_id, :name => :projects_trackers_project_id # Associates all trackers to all projects (as it was before) tracker_ids = Tracker.all.collect(&:id) Project.all.each do |project| project.tracker_ids = tracker_ids end end def self.down drop_table :projects_trackers end end