1. No more before_filter

undefined method 'before_filter' before_filter has been deprecated in Rails 5.0 and removed in 5.1.

2. halt_callback_chains_on_return_false is deprecated

ActiveSupport.halt_callback_chains_on_return_false= is deprecated and will be removed in Rails 5.2.

3. Passing a class to the class_name is deprecated

Passing a class to the 'class_name' is deprecated and will raise an ArgumentError in Rails 5.2.
It eagerloads more classes than necessary and potentially creates circular dependencies. Please pass the class name as a string:

This warning message was due to passing a class to `class_name` option when specifying associations – this is no longer recommended‘

- has_one :contact, class_name: UserContact
+ has_one :contact, class_name: 'UserContact

$ rails generate
Usage: rails generate GENERATOR [args] [options]
...........
Rails:
assets
channel
controller
generator
helper
integration_test
jbuilder
job
mailer
migration
model
resource
responders_controller
scaffold
scaffold_controller
task
.............

• controller: The Rails controller coordinates the interaction between the user, the views, and the model.
• helper: Code in helpers is included in the corresponding view. We can move big loops, method calls or other logic into a method in the helper.
• mailer: It allows for sending and receiving emails from and to your application.
• migration: Rails Migration allows you to use Ruby to define changes to your database schema.
• model: It is Ruby class that talk to the database, store and validate data, perform the business logic.
• scaffold: It refers to the auto-generation of a simple set of a model, views and controller usually for a single table.

-h, [–help] # Print generator’s options and usage -p, [–pretend] # Run but do not make any changes -f, [–force] # Overwrite files that already exist -s, [–skip] # Skip files that already exist -q, [–quiet] # Suppress status output

Generators

• rails generate model ModellName

It generates the model and the associated database table. For example, we can add a new model to the app called User with fields name and age as,

Eg:  rails g model User name: string age: integer

• rails generate controller ListController show edit

It generates controller. It is used if you are creating static views or non-CRUD related features. Let’s create a user controller that will manage the data flow and view for each users.

Eg:  rails g controller users

• rails generate scaffold ModelName ControllerName

Generates Scaffold. Let’s create a scaffold User with edit and view actions.

Eg:  rails g scaffold User edit view

• rails generate migration AddNewTable

Generates Table to migrate. We can create migration for adding a table as

Eg:  rails g migration User

• rails generate plugin PluginName

Generates Plugin.

Eg:  rails g plugin rails_plugin

• rails generate integration_test TestName

Generates Integration Test.

Eg:  rails generate integration_test User

• rails generate session_migration

Generates Session Migration.

Creating Generators with Generators

$ rails generate generator initializer
 create lib/generators/initializer
 create lib/generators/initializer/initializer_generator.rb
 create lib/generators/initializer/USAGE
 create lib/generators/initializer/templates

class InitializerGenerator < Rails::Generators::NamedBase
  source_root File.expand_path("../templates", __FILE__)
end

First, notice that we are inheriting from Rails::Generators::NamedBase instead of Rails::Generators::Base. This means that our generator expects at least one argument, which will be the name of the initializer.

Customizing Rails generators

config.generators do |g|
  g.orm :active_record
  g.template_engine :erb
  g.test_framework :test_unit, fixture: false
  g.stylesheets false
  g.javascripts false
end

References

• https://learn.co/lessons/rails-generators-readme
• https://www.tutorialspoint.com/ruby-on-rails/rails-generators.htm
• http://www.agmprojects.com/blog/building-a-rails-generator-and-packing-it-into-a-gem

<%= line_chart data, adapter: "google" %> <!-- or highcharts -->

<%= line_chart User.group_by_day(:created_at).count %>

In the above example, I have just shown you how we can make a line chart.Similarly, you can create Pie chart, Column chart, Bar chart, Area chart, Scatter chart, Geo charts, Timeline(Google Charts)etc. All you need is that one line of Ruby code. Cool, isn’t it!!

class ViewsController < ApplicationController
  def show
    @view = View.all
  end
  def views_by_day
    render json: View.group_by_day(:viewed_at, format: "%B %d, %Y").count
  end
end

<div class="container">
  <h3>Views By Day</h3>
  <%= line_chart views_by_day_view_path %>
</div>

<%= line_chart @.map { |view|
 {name: view.name, data: view.feats.group_by_week(:created_at).count}
} %>

<%= line_chart Feat.view(:view_id).group_by_week(:created_at).count %>

References

• http://chartkick.com/
• https://ankane.github.io/chartkick.js/examples/

CREATE INDEX index_name
ON prices (user_id);

add_index :prices, :user_id

CREATE INDEX index_name
ON user_views (user_id, article_id);

add_index :user_views, [:user_id, :article_id]

scope :articles, where(:spam => 'true')

CREATE INDEX index_name
on articles (spam is true);

add_index :articles, :spam, name: "index_articles_on_spam", where: "(spam IS true)"

DROP INDEX index_name;

remove_index :books, :created_at

• Index Primary key
• Index Foreign key
• Index all columns you would be passing into where clause
• Index the keys used to Join tables
• Index the date column (if you are going to call it frequent, like rankings of a particular date)
• Index the type column in an STI or polymorphism.
• Add partial index to scopes
• Do not index tables with a lot of read, write
• Do not index tables you know that will remain small, all through out its life time
• Do not index columns where you will be manipulating lot of its values.

User.find(156).withdraw(1000)
User.find(157).deposit(1000)

User.transaction do
  User.find(156).withdraw(1000)
  User.find(157).deposit(1000)
end

@user.transaction do
end

User.transaction do
end

User.transaction do
  Order.create order_attributes
  Purchase.create purchase_attribute
end

User.transaction do
  User.create(username: 'Kotori')
  User.transaction do
    User.create(username: 'Nemu')
    raise ActiveRecord::Rollback
  end
end

config.generators do |g|
  g.helper false
  g.stylesheets false
  g.javascripts false
  g.view_specs false
end

class Projects < ActiveRecord::Base
  has_many :tasks
end
class Task < ActiveRecord::Base
  belongs_to :project
end

class Task < ActiveRecord::Base
  belongs_to :project, counter_cache: true
end

class AddTasksCounterCacheToProjects < ActiveRecord::Migration[5.0]
  def change
    add_column :projects, :tasks_count, :integer
  end
end

Project.find_each { |project| Project.reset_counters(project.id, :tasks) }

class Task < ActiveRecord::Base
  belongs_to :project, counter_cache: :not_the_default_column_name
end

<% Project.all.each do |project| %>
  <%= project.name %> (<%= project.tasks.size %>)
<% end %>

• :counter_cache is the optional attribute of a belongs_to relationship
• It requires the creation of an extra column (tasks_count) in the table which has the has_many relationship
• One can use another column name by passing the name along with :counter_cache option
• To use the counter_cache, one must use the “.size” method