通过发电机添加从Rails引擎宝石到应用程序的新迁移

Question

我正在用红宝石宝石构建Rails引擎。它包括一些迁移，现在被称为当您运行：

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时，出现此错误：

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

我希望它只是默默忽视的事实是已经有一个迁移，并继续到下一个迁移。 这样做的最佳方法是什么？

编辑：

每梅德的答案，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

Rails中作为例子使用migration_template，你也许可以检查destination = self.class.migration_exists?(migration_dir, @migration_file_name)，如果迁移已经存在，跳过打电话给migration_template。