Implementing HABTM counter_cache - between 2 models (Tag, Question)

console.rb

## I imagine this could be done in the migration, but it was giving me problems so I moved it to the model 
## and just did it on the command line
 
> Tag.reset_questions_count

migration-sometimestamp.rb

class AddTagCounterToQuestion < ActiveRecord::Migration
  def up
    add_column :tags, :questions_count, :integer, default: 0, null: false
  end
  
  def down
    remove_column :tags, :questions_count
  end
    
end

question.rb

class Question < ActiveRecord::Base
  ## the validates_tag method is just to prevent duplicate tags being added to the db - not fully necessary for this exercise, 
  ## but I figured I would leave it just in case
  has_and_belongs_to_many :tags, before_add: :validates_tag
  
  after_create :increment_tags_counter
  after_destroy :decrement_tags_counter
  
  def validates_tag(tag)
    self.tags.include? tag
  end
 
  def increment_tags_counter
    self.tags.each do |t|
      Tag.find_by_name(t.name).questions_count += 1
    end
  end
 
  ## I haven't tested the callback on this, but it should work. What I am not 100% sure of is if the record is saved even
  ## a destroy, such that we can call `self.tags` on that same record and it works. If it doesn't work, then this can just
  ## be moved to a 'before_destroy'.
  
  def decrement_tags_counter
    self.tags.each do |t|
      Tag.find_by_name(t.name).questions_count -= 1
    end
  end
 
end

tag.rb

class Tag < ActiveRecord::Base
  attr_accessible :name, :questions_count
  
  has_and_belongs_to_many :questions, uniq: true
 
  def self.reset_questions_count
    Tag.all.each do |t|
      question_count = t.questions.count
      t.update_attributes(:questions_count => question_count)
    end
  end  
 
end