Order by count of has_many :through items in Rails 3

问题

If I have 3 models:

Model Section

Model User

has_many :votes

Model Vote

belongs_to :user

and inside ModelSection

has_many :users
has_many :votes, :through => :users

How to get the Sections list ordered by votes quantity using the AR associations?

回答1:

The most reasonable way to do this is to use a subquery written as raw SQL for ordering the result as follows...

Section.order(
  '(select count(1) from votes inner join users on votes.user_id=users.id where users.section_id=sections.id)'
)

回答2:

Section.joins(users: :votes).group(:id).order('COUNT(*)')

来源：https://stackoverflow.com/questions/11623226/order-by-count-of-has-many-through-items-in-rails-3