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.

Simple, user-friendly cancel links for your Rails forms

The default Rails view generator includes back links on form-related view templates, so if users change their mind they can easily get out of the form and on to something else. However, these links are static. What do you do if you allow users to access the form from multiple views (say, an index and a show).

Here’s a simple but effective solution I came up with: Instead of passing a static URL, I pass the HTTP referrer environment variable as the location. That way users are taken back to the page from which they opened the form to begin with.

Here’s how it works. Most of the code resides in the application_helper.rb file:

  module ApplicationHelper
    include Rails.application.routes.url_helpers

    def cancel_link
      return link_to 'Cancel', request.env["HTTP_REFERER"], 
        :class => 'cancel', 
        :confirm => 'Are you sure? Any changes will be lost.'
    end
  end

You’ll need to include Rails.application.routes.url_helpers in order to access link_to from a helper method. Then you add the helper method itself, which does nothing more than return a cancel link. Mine uses an old-style :confirm message; you can spruce it up with some less obtrusive if you’d like.

If I need a cancel link in a view, I just add

  <%= cancel_link %>

The result: a flexible, reusable cancel option that’s much more user-friendly.

Routing Concerns - Rails 4

The Rails config/routes.rb file encapsulates all the mappings from URLs to controller actions. Over the years, helpful additions have been added to slim this file down so that as developers, we can stop repeating ourselves. One example of this was the routing method resources, which maps four named routes to seven controller actions based on the HTTP request method.

As of Rails 4, routing concerns have been added to the router. Routing concerns allows you to declare common routes, which can be mixed into other resources and routes.

Example

A common example of duplication in the config/routes.rb file happens when a polymorphic association is nested under a parent resource.

Always add DB index

Always add index for foreign key, columns that need to be sorted, lookup fields and columns that are used in a GROUP BY. This can improve the performance for sql query. If you're not sure which column need to index , I recommend to use https://github.com/fgrehm/lol_dba, which provide rake tasks to find missing indexes.

Bad Smell

class CreateComments < ActiveRecord::Migration
  def self.up
    create_table "comments" do |t|
      t.string :content
      t.integer :post_id
      t.integer :user_id
    end
  end

  def self.down
    drop_table "comments"
  end
end

By default, rails does not add indexes automatically for foreign key, you should add indexes by yourself.