Ruby / Rails：如何显示每年和每月的总和值？

Question

我有一个名为Receipt的模型，它有以下内容：

• date_of_purchase - datetime
• total_value - float

我有一个包含许多收据的数据库，例如：

收据1

• date_of_purchase = 2012-01-23
• total_value = 6

收据2

• date_of_purchase = 2012-01-04
• total_value = 70

收据3

• date_of_purchase = 2013-02-14
• total_value = 1.23

收据4

• date_of_purchase = 2013-02-06
• total_value = 90.34

...

收据123

• date_of_purchase = 2013-08-05
• total_value = 43.69

如何显示以下内容：

{2012 =＆gt; {1 =＆gt; 76}，2013 =＆gt; {2 =＆gt; 92.23,3 =＆gt; 34.43，...}}

Answer 1

以下应该工作

receipts = Receipt.find_by_sql("SELECT MONTH(date_of_purchase) AS month, 
                       YEAR(date_of_purchase) AS year, SUM(total_value) as sum
                       FROM receipts GROUP BY year, month")

receipts_hash = {}
receipts.each do |receipt|
  receipts_hash[receipt.year] = {} unless receipts_hash[receipt.year]
  receipts_hash[receipt.year][receipt.month] = receipt.sum
end