如何在 Rails 中按第二个订单 belongs_to 分组？

Question

I have a fairly simple problem in Ruby on Rails. I have three models: States, Cities & Stadiums

State has_many cities
City belongs_to State
City has_many Stadiums
Stadium belongs_to City

Stadium has a city_id column. City has a state_id column. Stadium does not have a state_id column. I can access state from stadium by stadium.city.state

I would like to perform a group count to count how many Stadiums there are in a State, similar to the below:

Stadium.group(:city).count

which works fine. In other words, I want to do something like this

Stadium.group(:state).count

, which doesn't work. Is it possible? How can I do that?

Answer 1

I don't believe it's possible in vanilla rails. You might be able to do it with a crafted SQL statement.

Alternatively, you can use the array method but may not be as performant...

Stadium.all.group_by(&:state).count