ruby-on-rails - 通过生成器添加从 Rails 引擎 gem 到应用程序的新迁移

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，如果我再次运行 rails g myengine:install，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的事实并继续进行下一次迁移。 执行此操作的最佳方法是什么？

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

使用 migration_template以 Rails 为例，您或许可以检查 destination = self.class.migration_exists?(migration_dir, @migration_file_name) 如果迁移已经存在，则跳过 migration_template 调用。