Streamlined ActiveRecord

gistfile1.rb

class Post < ActiveRecord::Base

  has_many :comments

  # SERVICES

  def comment(attributes)
    create_comment(attributes)
  end

  # COLLABORATION METHODS

  def create_comment(attributes)
    Comment.new(attributes.merge(post: self))
  end

  # COLLABORATION RULES

  def add_comment?(comment)
    constrain_number_of_comments
  end

  def constrain_number_of_comments
    errors.add_to_base("Cannot exceed 10 comments") if comments > 10
  end
end

class Comment < ActiveRecord::Base

  belongs_to :post

  before_validation :verify_collaborations_rules

  def verify_collaboration_rules
    self.add_post?(post)
    post.add_comment?(self)
  end

  # COLLABORATION RULES

  def add_post?(post)
    true
  end
end