Question

I have such model structure:

class User < ActiveRecord::Base
  has_many :groups, :through => :user_groups
  has_many :orders
  has_many :user_groups
end

–

class UserGroup < ActiveRecord::Base
  belongs_to :group
  belongs_to :user
end

–

class Group < ActiveRecord::Base
  has_many :user_groups
  has_many :users, :through => :user_groups
end

In model group i have field markup.
How can i for every user via it’s user_groups get group’s markup field?

I try so:

user.user_groups.each do |u|
  summ += u.groups.markup
end

Sure it is not working… But how to fetch data from third model?

Answer 1

user.groups.map(&:markup).sum should do it just fine

EDIT:

I used #flat_map because I was thinking that it was a nested array. But has_many :through would combine it into a single result list, so #map will be fine

EDIT2:

In discussion with @VladisAzamaris, it was pointed out that the markup column is a float, so sum is more appropriate than join