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Anton Shemerey
@shemerey
Single Responsibility Principle в Руби
и почему instance/class variables это ОЧЕНЬ пл

each object should have
one and
only one responsibility

Dear Anton Shemerey.
Thank you for your patronage. This letter is to confirm that your order from
Doe Books has been filled and should arrive within 15 days.
Shipping books at the book rate generally slows delivery. As you know, payment
in full ($20.75) is due by the end of the month.
Thank you for doing business with Doe. We look forward to serving you again.
If you have questions regarding the new pricing please contact support.
--
Sincerely yours, John Peter
Doe Books
720 S Michigan Ave
Chicago, IL, United States
+1 312-922-4400
Order Confirmation Page

Dear. Anton Shemerey
in full ($20.75) is due by the end of the month.
Thank you for doing business with Doe Books. We look forward to serving you again.
If you have questions regarding the new pricing please contact support.
--
Doe Books
720 S Michigan Ave
+1 312-922-4400
Order Confirmation Page variables

Dear. {%user_full_name%}
{%company_name%} has been filled and should arrive within {%delivery_time%}.
in full ({%order_total%}) is due by the end of the month.
Thank you for doing business with {%company_name%}. We look forward to serving
you again. If you have questions regarding the {%price_url%} please
contact {%support_email%}.
--
Sincerely yours, {%owner_name%}
{%company_name%}
{%company_address%}
Order Confirmation Template

Data we have :(
• current_user.full_name #=> ‘Anton Shemerey’
• @order.estimated_delivery #=> ’15 days’
• @order.total #=> ‘<Money: @cents = 2075 ….’
• COMPANY_NAME #=> ‘Doe Books’
• $owner.full_name #=> ‘John Peter’
• @pricing_link #=> ‘http://example.com/price'
• $support_email = ‘support@example.com’
• @@company_address #=> ‘720 S Michigan Ave Chicago….’

Dear. <%= current_user.full_name %>
<%= COMPANY_NAME %> has been filled and should arrive
within <%= @order.estimated_delivery%>.
in full (<%= number_to_currency(@order.total) %>) is due by the end of the month.
Thank you for doing business with <%= COMPANY_NAME %>. We look forward to
serving you again. If you have questions regarding the <%= @pricing_link %> please
contact <%= email_to(“Support”, $support_email) %>.
--
Sincerely yours, <%= $owner.full_name %>
<%= COMPANY_NAME %>
<%= @@company_address %>
Order Confirmation Template

THE Controller :)
class OrdersController < ApplicationController
....
def confirmation
@order = Order.find(params[:id])
end
....
end

Антон Шемерей «Single responsibility principle в руби или почему instanceclass variables это очень плохо»

Dear. <%= @current_user_full_name %>
<%= @company_name %> has been filled and should arrive
within <%= @estimated_delivery_time %>.
in full (<%= number_to_currency(@order_total) %>) is due by the end of the month.
Thank you for doing business with <%= @company_name %>. We look forward to
serving you again. If you have questions
regarding the <%= link_to(‘price’, @pricing_link) %> please
contact <%= email_to(“Support”, @support_email) %>.
--
Sincerely yours, <%= @owner_full_name %>
<%= @company_name %>
<%= @company_address %>
Order Confirmation Template Second Attempt

THE Controller :)
....
def confirmation
@current_user_full_name = current_user.full_name
@company_name = COMPANY_NAME
@estimated_delivery_time = @order.estimated_delivery
@order_total = @order.total
@pricing_link = 'http://example.com/price'
@support_email = 'support@example.com'
@owner_full_name = $owner.full_name
@company_address = @@company_address
end
....
end
Second Attempt

Dear. Anton Shemerey
in full ($0) is due by the end of the month.
Thank you for doing business with Doe Books. We look forward to serving you
again. If you have questions regarding the new pricing please contact support.
--
Doe Books
720 S Michigan Ave
+1 312-922-4400
Free Order !!!!

# ....
def confirmation
@current_user_full_name = current_user.full_name
@company_name = COMPANY_NAME
@estimated_delivery_time = @order.estimated_delivery
@order_total = @order.total
@pricing_link = 'http://example.com/price'
@support_email = 'support@example.com'
@owner_full_name = $owner.full_name
@company_address = @@company_address
end
# ....
end
binding.pry
require 'pry'; binding.pry

2.0.0-p353 :006 > @order_total
=> #<Money:0x007fc7afb23530 @cents=83991, @currency="USD", @b
WTF ?!?!?!?!

Dear. <%= @current_user_full_name %>
<%= @company_name %> has been filled and should arrive
within <%= @estimated_delivery_time %>.
in full (<%= number_to_currency(@order_total) %>) is due by the end of the month.
Thank you for doing business with <%= @company_name %>. We look forward to
serving you again. If you have questions
regarding the <%= link_to(‘price’, @pricing_link) %> please
contact <%= email_to(“Support”, @support_email) %>.
--
Sincerely yours, <%= @owner_full_name %>
<%= @company_name %>
<%= @company_address %>
Order Confirmation Template binding.pry
<%- require 'pry'; binding.pry %>

2.0.0-p353 :0016 > @order_total
=> #<Money:0x007fc7afb23530 @cents=0, @currency="USD", @bank=#<M
WTF ?!?!?!?!

GREP!!!
$ grep -iRn @order_total app | wc
#=> 151 1017 17348

How are rails instance
variables passed to views
?????

AbstractController::Rendering#view_assigns
module AbstractController
module Rendering
# ....
# This method should return a hash with assigns.
# You can overwrite this configuration per controller.
# :api: public
def view_assigns
protected_vars = _protected_ivars
variables = instance_variables
variables.reject! { |s| protected_vars.include? s }
variables.each_with_object({}) { |name, hash|
hash[name.slice(1, name.length)] = instance_variable_get(name)
}
end
# ....
end
end

module AbstractController
def view_context
view_context_class.new(
view_renderer, view_assigns, self)
end
end
AbstractController#view_context

GREP!!!
$ grep -iRn @order_total app/helpers | wc
#=> 2 8 143
Second Attempt
module ApplicationHelper
....
def current_cart_total
if current_user
if order = current_user.current_order
@order_total = order.total
end
else
@order_total = Money.new(0)
end
end
....
end

$ git blame | grep current_cart_total
Problem Fixed!

before_action :load_order, only: [:show, :update, :destroy]
def update
if @order.update_attributes(params[:order])
redirect_to :show
else
render 'edit'
end
end
private
def load_order
end
end
Controller.before_action

....
def order
@order ||= Order.find(params[:id])
end
....
end
Memoization

helper_method :order
def update
if order.update_attributes(params[:order])
redirect_to :show
else
render 'edit'
end
end
private
def order
@_order ||= Order.find(params[:id])
end
end
Controller.helper_method

• memoization / lazy loading
• encapsulating (getter, setter)
• barewords (method, local variable,
helper_method, ….)

#source_location, caller
def total_order
stack = caller
require 'pry'; binding.pry
...
end
<% self.method(:total_order).source_location %>

one action one @
• PRESENTER
• SERVICE OBJECT
• PROXY OBJECT
• VALUE OBJECT
• LOCALS
• HELPER_METHOD
You can always use following

#destroy_all_view_assigns
group :development, :test do
gem 'destroy_all_view_assigns'
end

https://github.com/shemerey/destroy_all_view_assigns
https://github.com/shemerey
https://www.facebook.com/shemerey
https://twitter.com/shemerey
https://www.linkedin.com/in/shemerey
Questions ???

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Антон Шемерей «Single responsibility principle в руби или почему instanceclass variables это очень плохо»

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