ruby-on-rails - 通过生成器将新的迁移从 Rails 引擎 gem 添加到应用程序

Question

我正在用 ruby​​ gem 构建 Rails 引擎。它现在包括一些在您运行时调用的迁移：

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rails g myengine:install再次运行，它会失败并出现以下错误：

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存在迁移并继续进行下一次迁移的事实。最好的方法是什么？

编辑：

根据 Dmitry 的回答，这是我的解决方案：

  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

Answer 1

以Rails 中的migration_template为例，您也许可以检查destination = self.class.migration_exists?(migration_dir, @migration_file_name)是否存在迁移，如果迁移已经存在，则跳过migration_template调用。