A#
DRYing up model codes#
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. Using concerns we can extract this common code in a separate module Commentable.
For this create a commentable.rb file in app/models/concerns.
module Commentable
extend ActiveSupport::Concern
included do
has_many :comments, as: :commentable
end
# for the given article/event returns the first comment
def find_first_comment
comments.first(created_at DESC)
end
module ClassMethods
def least_commented
#returns the article/event which has the least number of comments
end
end
end
And now your models look like this :
Comment Model:
class Comment < ActiveRecord::Base
belongs_to :commentable, polymorphic: true
end
Article Model:
class Article < ActiveRecord::Base
include Commentable
end
Event Model:
class Event < ActiveRecord::Base
include Commentable
end
Skin-nizing Fat Models.#
Consider a Event model. A event has many attenders and comments.
Typically, the event model might look like this
class Event < ActiveRecord::Base
has_many :comments
has_many :attenders
def find_first_comment
# for the given article/event returns the first comment
end
def find_comments_with_word(word)
# for the given event returns an array of comments which contain the given word
end
def self.least_commented
# finds the event which has the least number of comments
end
def self.most_attended
# returns the event with most number of attendes
end
def has_attendee(attendee_id)
# returns true if the event has the mentioned attendee
end
end
Models with many associations and otherwise have tendency to accumulate more and more code and become unmanageable. Concerns provide a way to skin-nize fat modules making them more modularized and easy to understand.
The above model can be refactored using concerns as below: Create a attendable.rb and commentable.rb file in app/models/concerns/event folder
attendable.rb
module Attendable
extend ActiveSupport::Concern
included do
has_many :attenders
end
def has_attender(attender_id)
# returns true if the event has the mentioned attendee
end
module ClassMethods
def most_attended
# returns the event with most number of attendes
end
end
end
commentable.rb
module Commentable
extend ActiveSupport::Concern
included do
has_many :comments
end
def find_first_comment
# for the given article/event returns the first comment
end
def find_comments_with_word(word)
# for the given event returns an array of comments which contain the given word
end
module ClassMethods
def least_commented
# finds the event which has the least number of comments
end
end
end
And now using Concerns, your Event model reduces to
class Event < ActiveRecord::Base
include Commentable
include Attendable
end
This post helped me understand concerns.
app/models/trader.rb#
class Trader
include Shared::Schedule
end
app/models/concerns/shared/schedule.rb#
module Shared::Schedule
extend ActiveSupport::Concern
...
end
JJJ#
app/models/trader.rb#
class Trader
include Shared::Schedule
end
app/models/concerns/shared/schedule.rb#
module Shared::Schedule
extend ActiveSupport::Concern
...
end
module M
def self.included(base)
base.extend ClassMethods
base.class_eval do
scope :disabled, -> { where(disabled: true) }
end
end
def instance_method
...
end
module ClassMethods
...
end
end
After refactoring with ActiveSupport::Concern.
require 'active_support/concern'
module M
extend ActiveSupport::Concern
included do
scope :disabled, -> { where(disabled: true) }
end
class_methods do
...
end
def instance_method
...
end
end
Example 2: Handle module dependencies gracefully.
module Foo
def self.included(base)
base.class_eval do
def self.method_injected_by_foo_to_host_klass
...
end
end
end
end
module Bar
def self.included(base)
base.method_injected_by_foo_to_host_klass
end
end
class Host
include Foo # We need to include this dependency for Bar
include Bar # Bar is the module that Host really needs
end
After refactoring with ActiveSupport::Concern
require 'active_support/concern'
module Foo
extend ActiveSupport::Concern
included do
def self.method_injected_by_foo_to_host_klass
...
end
end
end
module Bar
extend ActiveSupport::Concern
include Foo
included do
self.method_injected_by_foo_to_host_klass
end
end
class Host
include Bar # It works, now Bar takes care of its dependencies
end
For example I want in my application where attribute create_by exist update there value by 1, and 0 for updated_by
module TestConcern
extend ActiveSupport::Concern
def checkattributes
if self.has_attribute?(:created_by)
self.update_attributes(created_by: 1)
end
if self.has_attribute?(:updated_by)
self.update_attributes(updated_by: 0)****
end
end
end
If you want to pass arguments in action
included do
before_action only: [:create] do
blaablaa(options)
end
end
after that include in your model like this:
class Role < ActiveRecord::Base
include TestConcern
end
MOre sample#
as#
class Comment < ActiveRecord::Base
attr_accessible :body, :email, :name, :article_id
belongs_to :article
validates :name, :email, :body, :presence => true
validates :article_should_be_published
def article_should_be_published
errors.add(:article_id, "is not published yet") if article && !article.published?
end
end
class Article < ActiveRecord::Base
attr_accessible :body, :published_at, :title
validates :title, :presence => true
validates :body, :presence => true
belongs_to :user
has_and_belongs_to_many :categories
has_many :comments
scope :published, where("articles.published_at IS NOT NULL")
scope :draft, where("articles.published_at IS NULL")
# recent post from < a month ago - see pg 103 of tutorial
# scope :recent, lambda { published.where("articles.published_at > ?", 1.month.ago.to_date)}
scope :where_title, lambda { |term| where("articles.title LIKE ?", "%#{term}%") }
def long_title
"#{title} - #{published_at}"
end
def published?
published_at.present?
end
end