Question

I have four rails models called user, school, subscription and news_item. I a situation where a user subscribes to school to get news notification from that school, how is it possible to display all the news_items that a user is subscribed to.

my user model has this

  belongs_to :school
  has_many :schools, :through => :subscriptions
  has_many :subscriptions

  def subscribe_to(school)
    subscribe = subscriptions.build(:school_id => school.id)
    if !subscribe.save
      logger.debug "you have already subscribed to '#{school.name}'"
    end
  end

after_create :create_school_subscription
def create_school_subscription
school = self.school_street
self.subscriptions.build(:school_id => school.id)
end

and my subscription model has

  belongs_to :user
  belongs_to :school, :class_name => 'School'
  validates_uniqueness_of :school_id, :scope => :user_id
  validates_presence_of :user_id, :school_id

my school model has

  has_many :users
  has_many :news_items

finally my news_item model has

belongs_to :school

with all this put in place how can i get all the news a user is subscribed to through the school

Answer 1

class NewsItem
  scope :news_for, lambda { |user|
    {
        :joins      => "INNER JOIN subscriptions on news_items.school_id = subscriptions.school_id",
        :conditions => "subscriptions.user_id = #{user.id}"
    }
  }
end

NewsItem.news_for(User.first)