ruby-on-rails – 将新的迁移从Rails引擎gem添加到应用程序通过

rails g myengine:install

生成器中的代码如下：

module MyEngine
  module Generators
    class InstallGenerator < ::Rails::Generators::Base
      include Rails::Generators::Migration

      source_root File.expand_path('../templates',__FILE__)

      # ...

      def copy_migrations
        migration_template "migrations/migration1.rb","db/migrate/migration1.rb"
        migration_template "migrations/migration2.rb","db/migrate/migration2.rb"
      end

      # ...
    end
  end
end

但是,如果我运行rails g myengine：再次安装,则会失败,并显示此错误：

Another migration is already named migration1: /Users/jh/Code/Web/demoapp/db/migrate/20130327222221_migration1.rb

我希望它只是默默地忽略已经有迁移的事实,并继续下一次迁移.这样做最好的方法是什么？

编辑：

根据德米特里的回答,这是我的解决办法：

def copy_migrations
    copy_migration "migration1"
    copy_migration "migration2"
  end

protected

  def copy_migration(filename)
    if self.class.migration_exists?("db/migrate","#{filename}")
      say_status("skipped","Migration #{filename}.rb already exists")
    else
      migration_template "migrations/#{filename}.rb","db/migrate/#{filename}.rb"
    end
  end