gistfile1.rb

class Teacher < User  
  has_many :grades, :through => :teachings, :uniq => true
  has_many :teachings               
  
  has_many :subjects, :through => :teachings, :uniq => true
  
  def teaching_grades(organization) 
    grades.where('teachings.grade_id' => Grade.where(:organization_id => organization.id))    
  end
  
end

class Organization < ActiveRecord::Base
  #attr_accessible :name, :slug
  has_many :users, :through => :memberships
  has_many :memberships
  has_many :grades
  has_many :subjects
  has_many :events                                                                                            
  has_many :attendances
  has_many :resources
  
  has_many :admins, :through => :memberships, :source => :user, :conditions => ["memberships.role = 'admin'"]
  has_many :teachers, :through => :memberships, :source => :user, :conditions => ["memberships.role = 'teacher'"]
  has_many :students, :through => :memberships, :source => :user, :conditions => ["memberships.role = 'student'"]
end  

class Teaching < ActiveRecord::Base
  #attr_accessible :teacher_id, :grade_id, :subject_id  
  belongs_to :subject
  belongs_to :teacher
  belongs_to :grade   
  
  validates :grade_id, :presence => true
  validates :subject_id, :presence => true
  
  scope :distinct_subjects, group(:subject_id).includes(:subject => :grades)
  
end  

class Grade < ActiveRecord::Base
  #attr_accessible :name, :institute_id    
  
  belongs_to :organization
  has_many :teachers, :through => :teachings 
  has_many :subjects, :through => :teachings  
  has_many :teachings
  
  has_many :students, :through => :attendances, :source => :user
  has_many :attendances
 
  has_many :resources, :through => :publications
  has_many :publications
  has_many :public_events, :through => :event_publications, 
           :class_name => 'Event',
           :conditions => ['event_publications.public = ?', true]
  has_many :event_publications

  
end 

// generated queries:

 Grade Load (1.4ms)  SELECT DISTINCT `grades`.* FROM `grades` INNER JOIN `teachings` ON `grades`.id = `teachings`.grade_id WHERE `teachings`.`grade_id` IN (5, 6) AND ((`teachings`.teacher_id = 1)) LIMIT 1
  Grade Load (0.5ms)  SELECT DISTINCT `grades`.* FROM `grades` INNER JOIN `teachings` ON `grades`.id = `teachings`.grade_id WHERE `teachings`.`grade_id` IN (5, 6) AND ((`teachings`.teacher_id = 1))