Model Concerns in Rails 4

Concerns in Model can be used to skin-nize fat models as well as DRY up your model codes. Here is an explanation with examples:

Consider a Article model, a Event model and a Comment Model. A article or A event has many comments. A comment belongs to either article or event.

Traditionally, the models may look like this:

Comment Model:

class Comment < ActiveRecord::Base
  belongs_to :commentable, polymorphic: true
end

Article Model:

class Article < ActiveRecord::Base
  has_many :comments, as: :commentable 

  def find_first_comment
    comments.first(created_at DESC)
  end

  def self.least_commented
   #return the article with least number of comments
  end
end

Event Model

class Event < ActiveRecord::Base
  has_many :comments, as: :commentable 

  def find_first_comment
    comments.first(created_at DESC)
  end

  def self.least_commented
   #returns the event with least number of comments
  end
end

As we can notice, there is a significant piece of code common to both Event and Article Model. Using concerns we can extract this common code in a separate module Commentable.

Adding Password Complexity Validations To Devise

Here we have a typical Devise user model. What’s new is the password complexity validation.

class User < ActiveRecord::Base
  devise :database_authenticatable, :registerable, :recoverable, :rememberable, :trackable, :validatable
  attr_accessible :email, :password, :password_confirmation, :remember_me,

  validate :password_complexity

  def password_complexity
    if password.present? and not password.match(/^(?=.*[a-z])(?=.*[A-Z])(?=.*\d). /)
      errors.add :password, "must include at least one lowercase letter, one uppercase letter, and one digit"
    end
  end
end