class Quiz < ActiveRecord::Base
  has_many :questions, :dependent => :destroy
end
 
class Question < ActiveRecord::Base
  belongs_to :quiz, :counter_cache => true
end
 
# Counter cache doesn't work in this case:
questions.each do |question|
  quiz.questions << question
end
assert_equal quiz.questions.size, quiz.questions.count  # false!
 
# It does work in this one.
questions.each do |question|
  question.quiz = quiz
  question.save
end
assert_equal quiz.questions.size, quiz.questions.count  # true!
 
# AR is inconsistent sometimes  :(