活动记录每日计数数组 w.r.t created_at 或 updated_at

Question

我正在做一个学校项目，我有表 class_standard 和 enrollments

enrollments belongs_to class_standard 和 class_standard 有很多 enrollments.

enrollments 是 created_at 在不同的日子。我想获取数组中过去 30 天的每日注册人数。

即[第 1 天、第 2 天、第 3 天的注册人数......]

Answer 1

这是获取每天创建的注册人数并将其存储在数组中的代码示例。

arr = [] #initialize an array
(0..29).each do |x| #run a loop for 30 days
  date = Time.now - x.days #get a specific day
  arr << Enrollment.where(created_at: date.midnight..date.end_of_day).count #get count of enrollments on a specific day and add this to your array
end
arr = arr.reverse #reverse the array, because you want the today's count as last item of the array

Answer 2

您想要做的是 select 按天分组的计数。具体如何实现取决于所使用的数据库。

Postgres:

date_trunc('day', created_at)

MySQL:

date_format(created_at, '%Y-%m-%d')

对于其他数据库，请查看日期函数的文档。

总的来说你想要的查询是这样的：

SELECT 
  count(*) AS count, 
  date_trunc('day', created_at) AS day 
FROM "enrollments" 
WHERE (created_at >= ?) -- one month ago 
GROUP BY day 
ORDER BY day

我们可以在 ActiveRecord 中这样写：

Enrollment.select("count(*) AS count, to_char(created_at, 'YYYY-MM-DD') AS day")
  .group("day")
  .order("day")
  .where(created_at: (1.month.ago..Time.current))

但这给出了 ActiveRecord::Relation 的记录，这不是很有用。要获取原始查询值，我们要使用 #select_all.

sql = Enrollment.select("count(*) AS count, date_trunc('day', created_at) AS day")
  .group("day")
  .order("day")
  .where("created_at >= ?", 1.month.ago)
  .to_sql

results = Enrollment.connection.select_all(sql)

当您将结果转换为数组时，您将得到一个哈希数组：

[{"count"=>10, "day"=>"2018-10-20 00:00:00"}, {"count"=>10, "day"=>"2018-10-21 00:00:00"}, {"count"=>10, "day"=>"2018-10-22 00:00:00"}, {"count"=>10, "day"=>"2018-10-23 00:00:00"}, {"count"=>10, "day"=>"2018-10-24 00:00:00"}, {"count"=>10, "day"=>"2018-10-25 00:00:00"}, ...]

您可以通过映射数组来提取计数：

results.map {|r| r["count"] }

如果您只想获得一个（或多个）ClassStandards 的结果，只需在 where 子句中添加一个附加条件：

sql = Enrollment.select("count(*) AS count, date_trunc('day', created_at) AS day")
  .group("day")
  .order("day")
  .where("created_at >= ?", 1.month.ago)
  .where(class_standard: @class_standard)
  .to_sql

或者你取消关联：

sql = @class_standard.enrollments
  .select("count(*) AS count, date_trunc('day', created_at) AS day")
  .group("day")
  .order("day")
  .where("created_at >= ?", 1.month.ago)
  .to_sql

Answer 3

如果您想计算所有天数，包括没有任何注册的天数：

daily_enrollments = []
i = 29
while i >= 0
  daily_enrollments >> Enrollments.where( created_at: Time.zone
                                                          .now
                                                          .beginning_of_day-i.day..
                                                      Time.zone
                                                          .now
                                                          .end_of_day-i.day).count

  i = i-1
end

输出示例

[0,0,0,5,4,0,0,0,5,0,23,0,0,23,0,0,1,0,11,0,21,32,44,0,0,9,6,3,22,1]

这将为您提供所有 30 天的数组。但这似乎不是有效的代码。这将为每条记录运行 30 个查询。

对我来说更好的方法是将 created_at 上的记录分组，并获取有一些记录的日子的记录。即排除没有记录的天数。

Enrollments.where(created_at: Time.current - 30.days..Time.current)
           .group("date(created_at)")
           .count
           .sort
           .to_h

输出示例

{Mon, 19 Nov 2018=>12}

活动记录每日计数数组 w.r.t created_at 或 updated_at

Active records daily count array w.r.t created_at or updated_at

activerecord

ruby-on-rails

rails-activerecord