engine_migrations.rb

module EngineWithMigrations
  class Engine < ::Rails::Engine
    isolate_namespace EngineWithMigrations
    
    initializer :append_migrations do |app|
      unless app.root.to_s.match root.to_s
        app.config.paths['db/migrate'] += config.paths['db/migrate'].expanded
      end
    end
  end
end