如何将方法应用于 ActiveRecord 对象的集合 [英] How do you make a method apply to a collection of ActiveRecord objects

问题描述

目前，如果我想将一个方法应用于一组 ActiveRecord 对象，我必须像这样构造调用:

Currently, if I want to apply a method to a group of ActiveRecord objects, I have to structure the call like so:

messages = Message.find(:all)
csv = Message.to_csv(messages)

如何定义方法，使其结构如此?

How can I define the method so it's structured like so?

messages = Message.find(:all)
csv = messages.to_csv

这是当前的型号代码:

require 'fastercsv'
class Message < ActiveRecord::Base
  def Message.to_csv(messages)
    FasterCSV.generate do |csv|
      csv << ["from","to", "received"]
      for m in messages
        csv << [m.from,m.to,m.created_at]
      end
    end
  end
end

推荐答案

以下内容将对包含在消息数组中的所有实例调用 to_csv.

The following will call to_csv on all instances included in the messages array.

messages = Message.find(:all)
csv = messages.map { |message| message.to_csv }

在 Rails、Ruby 1.9 或 Symbol#to_proc 中，您也可以通过其他方式将其缩短为:

In Rails, in Ruby 1.9 or with Symbol#to_proc available through other means, you can also shorten it to:

csv = messages.map(&:to_csv)

当您想要进行更复杂的操作时，较长的形式很有用:

The longer form is useful when you want to make a more complex operation:

csv = messages.map { |message| 
  if message.length < 1000
    message.to_csv
  else
    "Too long"
  end
}

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