Rails 中的多列分组和总计

Question

我的数据看起来像这样

 ___________________________________
|name  date      status    location |
|Tom   1/1/2010  Ready     Home     |
|Tom   1/1/2010  Ready     Home     |
|Bill  1/18/2010 Go        Work     |
|Bob   2/19/2010 Ready     Field    |
|Bob   2/19/2010 Ready     Field    |
|Wil   4/5/2010  Steady    Work     |
|Wil   4/5/2010  Steady    Work     |
|Wil   4/5/2010  Steady    Work     |
|Wil   4/5/2010  Steady    Home     |
|Bill  7/14/2010 Stop      Home     |
|___________________________________| 

我需要对其进行分组/计数，以便看起来像这样

Name   Date      Location    Status   Count
Tom    1/1/2010  Home        Ready    2
Bill   1/18/2010 Work        Go       1
Bill   7/14/2010 Home        Stop     1
Bob    2/19/2010 Field       Ready    2
etc.....

Answer 1

有时，根据数据的格式和属性，执行此操作的最佳方法很棘手。但一般来说，您可以使用 :group 参数“nofollow">ActiveRecord#find。

Model.all(:select => 'COUNT(*) AS count, name, date, location, status', :group => 'name')

或者，如果使用 Rails 3

Model.all.select('COUNT(*) AS count, name, date, location, status').group('name')

如果您始终打算根据此关系对数据进行分组，请考虑将其添加为模型的默认范围。

class Model < ActiveRecord::Base
  default_scope select('COUNT(*) AS count, name, date, location, status')
  default_scope group('name')
end