今天的SQL查询[重复](SQL query today [duplicate])

 好的，所以我之前已经处理过这个问题，作为一种设计模式，它不是理想的做事方式IMO，但它有时是唯一的方法，特别是如果你没有直接的磁盘写访问权限，就像你一样如果部署在Heroku上。 这是解决方案。 
 
class Global < ActiveRecord::Base
  validate :only_one

  private

  def only_one
    if Global.count >= 1
      errors.add :base, 'There can only be one global setting/your message here' 
    end
  end
end
 
 如果您有直接磁盘访问权限，则可以创建一个YAML配置文件，您可以在用户编辑配置变量时进行读/写/转储。 
 
 例如，您可以在config/locales/globals.yml有一个yaml文件 
 
 当你想编辑它时，你可以写 
 
filepath = "#{Rails.root}/config/locales/globals.yml"
globals = YAML.load(File.read("#{Rails.root}/config/locales/globals.yml"))
globals.merge!({ sales_tax: 0.07 })

File.write(filepath) do |f|
  f.write YAML.dump(globals)
end
 
 更多关于ruby yaml文档 
 
 您还可以使用JSON，XML或您想要的任何标记语言 

Ok, so I've dealt with this before, as a design pattern, it is not the ideal way to do things IMO, but it can sometimes be the only way, especially if you don't have direct disk write access, as you would if deployed on Heroku. Here is the solution.
 
class Global < ActiveRecord::Base
  validate :only_one

  private

  def only_one
    if Global.count >= 1
      errors.add :base, 'There can only be one global setting/your message here' 
    end
  end
end
 
If you DO have direct disk access, you can create a YAML config file that you can read/write/dump to when a user edits a config variable.
 
For example, you could have a yaml file in config/locales/globals.yml
 
When you wanted to edit it, you could write
 
filepath = "#{Rails.root}/config/locales/globals.yml"
globals = YAML.load(File.read("#{Rails.root}/config/locales/globals.yml"))
globals.merge!({ sales_tax: 0.07 })

File.write(filepath) do |f|
  f.write YAML.dump(globals)
end
 
More on the ruby yaml documentation
 
You could also use JSON, XML, or whatever markup language you want