Question

在我的模型中，我有一个函数，结果数组是

...#<DailyStat subject: "Auditing Theory", topic: "Audit Planning", item_count: 3, correct_item_count: 0>
#<DailyStat subject: "Auditing Theory", topic: "Audit Reporting", item_count: 2, correct_item_count: 0>
#<DailyStat subject: "Auditing Theory", topic: "Audit Sampling", item_count: 2, correct_item_count: 2>...

（DailyStat是一个模特。）我需要添加一定百分比的item_count / correct_item_count以保证准确性。如何转换并添加其他符号。这是当前的代码，它不起作用。

.select("subject, topic, sum(correct_item_count) as correct_item_count, sum(item_count) as item_count") # can't I just add the computation here
.map{|row| row} # Supposed to convert from AR record to array
.map{|row| 
  row[:accuracy] = row[:correct_item_count]/row[:item_count]
  row
  }

这种方法是否更好，或者我执行select语句时应该进行计算（哪个更快？）

Answer 1

无需从SQL中获取它。数据库用于...数据，而不是计算。

您可以在DailyStat模型中轻松定义此类方法，并在需要时在视图或其他地方调用它。

class DailyStat < ActiveRecord::Base
  def accuracy
    return 0 if item_count == 0
    correct_item_count/item_count
  end
end

并使用它

stat = DailyStat.last
state.accuracy 
# There is no SQL involved

Answer 2

sql查询中的计算将比这更快。
你可以做这样的事情。

select("subject, topic, sum(correct_item_count) as correct_item_count, sum(item_count) as item_count, ((sum(item_count)/sum(correct_item_count))*100) as accuracy_percentage")

Ruby Active Record to array。你如何修改结果？

2 个答案: