ActiveRecord從組中獲取平均值

我正在嘗試在ActiveRecord 4中編寫此查詢，但無濟於事。ActiveRecord從組中獲取平均值

SELECT date, AVG(gain) AS avg_gain FROM counters WHERE (date > '2014-03-03' ) GROUP BY date ORDER BY date DESC;

所以我炒了一起：

Counter.select("date, AVG(gain) as avg_gain").where("date > '2014-03-03'").group(:date).order(date: :desc) 
=> #<ActiveRecord::Relation [#<Counter id: nil, date: "2014-04-01">, #<Counter id: nil, date: "2014-03-31">, #<Counter id: nil, date: "2014-03-30">, #<Counter id: nil, date: "2014-03-29">, #<Counter id: nil, date: "2014-03-28">, #<Counter id: nil, date: "2014-03-27">, #<Counter id: nil, date: "2014-03-26">, #<Counter id: nil, date: "2014-03-25">, #<Counter id: nil, date: "2014-03-24">, #<Counter id: nil, date: "2014-03-23">, ...]>

唯一的麻煩是，該結果不包含avg_gain列。有任何想法嗎？

來源

2014-04-01 if __name__ is None

當您使用select時，所選字段將添加到返回的關係中的實例。返回的結果不包括打印輸出中的所選字段。

訪問這些字段，就像你訪問一個列的屬性：

result = Counter.select("date, AVG(gain) as avg_gain").where("date > '2014-03-03'").group(:date).order(date: :desc) 
result.first.avg_gain # Prints expected value for the first Counter

來源

2014-04-01 18:46:23 vee

有什麼辦法，我可以掐出來？像'Counter.select（「date，AVG（gain）as avg_gain」）。其中（「date>'2014-03-03'」）。group（：date）.order（date：：desc）.pluck（：日期，「avg_gain」）'？ –

@JanNetherdrake你可以做'result.map {| counter | [counter [：date]，counter [：avg_gain]]}'返回像[[[date，avg]，[date，avg]，...] – MrYoshiji

ActiveRecord從組中獲取平均值

回答

相關問題