Adding Indexes and Foreign Keys to Database Migrations

Keep in mind that you’ll need a gem/plugin to do the “add_foreign_key” calls below.

class CreateRoles < ActiveRecord::Migration
  def self.up
    create_table :roles, :force => true do |t|
      t.string   :name,              :limit => 40
      t.string   :authorizable_type, :limit => 40
      t.integer  :authorizable_id
      t.timestamps
    end
    add_index :roles, :name
    add_index :roles, :authorizable_id
    add_index :roles, :authorizable_type
    add_index :roles, [:name, :authorizable_id, :authorizable_type], :unique => true
  end

  def self.down
    remove_index :roles, [:name, :authorizable_id, :authorizable_type]
    remove_index :roles, :authorizable_type
    remove_index :roles, :authorizable_id
    remove_index :roles, :name
    drop_table :roles
  end
end

class CreateRolesUsers < ActiveRecord::Migration
  def self.up
    create_table :roles_users, :id => false, :force => true do |t|
      t.integer  :user_id
      t.integer  :role_id
      # do not create timestamps for habtm table
      # t.timestamps
    end
    add_index :roles_users, :user_id
    add_index :roles_users, :role_id
    add_index :roles_users, [:user_id, :role_id], :unique => true
    add_foreign_key :roles_users, :users
    add_foreign_key :roles_users, :roles
  end

  def self.down
    remove_foreign_key :roles_users, :users
    remove_foreign_key :roles_users, :roles
    remove_index :roles_users, :user_id
    remove_index :roles_users, :role_id
    remove_index :roles_users, [:user_id, :role_id]
    drop_table :roles_users
  end
end