Question

該查詢工作正常，但作爲一個練習，我將如何轉換它利用ActiveRecord方法？

Model.find_by_sql("SELECT *, SUM(impressions) AS impressions, SUM(cost) AS cost 
        FROM display_stats 
        WHERE (created_at >= '#{(Date.today-2).to_time.strftime('%Y-%m-%d')}' 
          AND created_at <= '#{(Date.today-1).to_time.strftime('%Y-%m-%d')}') 
        GROUP BY banner_id 
        ORDER BY cost DESC") 

這裏是我的模型結構：

DisplayStat (id: integer, 
      banner_id: integer, 
      comments: string, 
      impressions: integer, 
      cost: integer, 
      created_at: datetime, 
      updated_at: datetime) 

是否可以寫上面的查詢，而無需使用原始的SQL？

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的運轉軌道3.1和MySQL 5.5

Answer 1

試試這個：

DisplayStat. 
    select("banner_id, SUM(impressions) AS impressions, SUM(cost) AS cost"). 
    where(:created_at => (2.days.ago.beginning_of_day..2.days.ago.end_of_day)). 
    group(:banner_id). 
    order("cost DESC") 

的日期範圍是從開始到一天結束的時候; 2天前。當您將日期範圍傳遞給條件散列時，rails會生成一個BETWEEN運算符。