Question

I have the following models:

class User < ActiveRecord::Base
  has_many :subscriptions, as: :subscribable
  has_many :user_to_high_school_subscriptions
  has_many :high_school_subscriptions, through: :user_to_high_school_subscriptions

  def all_subscriptions
    self.subscriptions + self.high_school_subscriptions.subscriptions
  end
end

class UserToHighSchoolSubscription < ActiveRecord::Base
  belongs_to :user
  belongs_to :high_school_subscription
end

class HighSchoolSubscription < ActiveRecord::Base
  has_many :user_to_high_school_subscriptions
  has_many :users, through: :user_to_high_school_subscriptions
  has_many :subscriptions, as: :subscribable
end

class Subscription < ActiveRecord::Base
  belongs_to :subscribable, polymorphic: true
end

Is there a clever way for me to get ALL Subscriptions that a User has.

I tried

u = User.first
subs = u.all_subscriptions

but that is erroring out (undefined method subscriptions' for #<ActiveRecord::Relation:). I think it’s choking when I try to use the has_many :subscriptions on the HighSchoolSubscription because a user has_many :high_school_subscriptions. (This line: self.high_school_subscriptions.subscriptions).

Is there a way to aggregate has_many on a has_many in Rails?

Running rails 3.2.1

Answer 1

self.subscriptions does not return an Array but ActiveRecord::Relation. That’s the reason why the + methods and does not work and your get the mentioned error. The simplest fix is to do it this way:

def all_subscriptions
  self.subscriptions.all + self.high_school_subscriptions.all.collect { |hss| hss.subscriptions.all }.flatten
end

The all method will trigger the database queries and return an array. Because a user might have many high school subscriptions and these also may has many subscriptions, you have to iterate over all high school subscriptions and collect their subscriptions. As you can see, this is a complete overkill.

Redesign your data model or just do it a different way.

Perhaps, scoping the Subscription model might be the way. Add it an attribute that would specify what kind of subscription it is and then you can completely remove the HighSchoolSubscription model.