如何在活动记录查询下方进行优化,该查询不返回属于日期范围的记录



我想要一个优化的AR(ActiveRecord(查询,因为我当前的AR查询多次查询数据库

假设模型巧克力具有列created_at。我的控制器中有以下 AR 查询:

for i in 1..4 
    @myHash[i] = Chocolate.where(created_at: (Time.now - i.hours)..(Time.now - (i-1).hours)).count    
end

上述查询从 db 检索 4 次(假设当前时间为 12:00(

Select COUNT(*) from Chocolate where created_at BETWEEN 11:00 AND 12:00
Select COUNT(*) from Chocolate where created_at BETWEEN 10:00 AND 11:00 
Select COUNT(*) from Chocolate where created_at BETWEEN 09:00 AND 10:00 
Select COUNT(*) from Chocolate where created_at BETWEEN 08:00 AND 09:00

如何更改查询,使其仅从数据库检索一次?

您可以使用如下查询:

Chocolate.where(Chocolate.arel_table[:created_at].gteq(4.hours.ago))
         .group("DATE_TRUNC('hour', created_at)")
         .count

它将返回一个哈希值,其中包含按小时分组的记录计数。

{"2019-02-12 00:00:00"=>152, "2019-02-12 01:00:00"=>57, "2019-02-12 02:00:00"=>132, "2019-02-12 03:00:00"=>132}

希望这有帮助。

尝试纯字符串条件:

Chocolate.where('created_at BETWEEN ? AND ?', (Time.now - i.hours), (Time.now - (i-1).hours))

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