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##########################################################
# polymorphic as module
##########################################################

# app/models/comment.rb
#

class Comment < ActiveRecord::Base
  belongs_to :commenter, :polymorphic => true
end

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rails generator dictionary

basic

$ rails g model user email age:integer

• data_type
  • integer
  • primary_key

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# ref: http://www.jimmycuadra.com/posts/metaprogramming-ruby-class-eval-and-instance-eval)

class Person
end

Person.class_eval do
  def say_hello
   "Hello!"
  end
end

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# rails migration

########################
# add column to exsting table
########################

def up
  add_column :users, :status, :string
  User.find_each do |user|
    user.status = 'active'

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# rails methods

# returns column_names arrays
Model.column_names

# returns attr_keys arrays
object.attributes.keys

# returns attr_keys values
object.attributes.values

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Alternative polymorphic model

Here's a fully working example:

# The migration file:
class CreateUserEntities < ActiveRecord::Migration
  def change
    create_table :user_entities do |t|
      t.integer :user_id

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Rails 4 with Rspec 3

Configure your Gemfile

# Gemfile
group :development, :test do
  gem 'rspec-rails', '~> 3.0.0'
  gem 'factory_girl_rails'
  gem 'capybara'

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Polymorphic Associations in Rails 4, Part2

reference:

Part1: astockwell.com

Part2: astockwell.com

PAIN POINT

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Polymorphic Associations in Rails 4

Adding a Polymorphic Association to Devise User Accounts

reference:

Part1: astockwell.com

Part2: astockwell.com

PROBLEM

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Single Table inheritance

reference: blog.thirst.co

In a nutshell, STI allows you to create subclasses of a particular database table. Using a single table, you can cast rows to specific objects that extend the base model.

how to create STI relationships in Rails

Lets say we have a model Computer