Presenters in Rails

Presenters!
(On Rails)
Mike Desjardins
@mdesjardins

Design Pattern?
Per our good friends at Wikipedia:
In software engineering, a design pattern is a general
reusable solution to a commonly occurring problem
within a given context in software design.

Design Pattern?

Observer

Design Pattern?

Observer
Factory

Design Pattern?

Observer
Factory Bridge

Design Pattern?

Observer
Factory Bridge
Singleton

Design Pattern?

Observer
Factory Bridge
Singleton

Decorator

Design Pattern?

Observer
Factory Bridge
Singleton

Visitor Decorator

Swell!

MVC! Note to any Microsoft
knuckleheads:
This is not a presentation on
“MVP.”

Model View
Controller
Controllers

Model Views

GOsh, What’s Wrong With
MVC?
As your project gets more complex, the
Controllers and Views become “bloated” despite
your best efforts.

These are just the filters in CityEats’ Orders
Controller!
skip_before_filter :protect_private_environments, except: [:new]
before_filter :set_user,
only: [:new, :credit_user_account, :create, :iframe, :payment_form, :offer_details]
# Are all three of these filters necessary? It doesn't seem so at a glance. -Tim
before_filter :load_restaurant,
only: [:new, :create, :iframe, :credit_user_account, :payment_form, :offer_details],
:if => lambda { |c| params[:restaurant_id].present? }
before_filter :load_restaurant_and_authenticate,
only: [:new],
:if => lambda { |c| params[:restaurant_id].present? || params[:restaurant_offer_id].present? }
before_filter :load_offer_and_set_restaurant,
only: [:new, :credit_user_account, :create, :payment_form, :offer_details],
:if => lambda { |c| params[:restaurant_offer_id].present? }
before_filter :require_restaurant,
only: [:new]
before_filter :merge_request_ip_address,
only: [:create]
around_filter :load_restaurant_time_zone,
only: [:new, :show, :create, :destroy, :iframe, :payment_form, :credit_user_account]
before_filter :load_watched_video,
only: [:create]
before_filter :init_reservation,
only: [:new, :iframe, :payment_form, :credit_user_account, :create, :offer_details]
before_filter :init_order,
only: [:new, :iframe, :payment_form, :credit_user_account, :create, :offer_details]
before_filter :set_price,
only: [:new, :create, :credit_user_account, :payment_form]
before_filter :init_gateway_request_filter,
only: [:new, :credit_user_account, :payment_form]

AW SHUCKS, Actions
too! create action:
Here’s the OrdersController’s
def create
if params[:iframe]
@styling = @restaurant.try(:restaurant_widget_customization) ||
RestaurantWidgetCustomization.new(:restaurant_id => @restaurant.try(:id))
@styling.merge(params["restaurant_widget_customization"]) if params["restaurant_widget_customization"].present?
end

@order.group_emailable = params[:group_emailable]
@reservation.landing_tag = cookies['landing_tag'] if cookies['landing_tag'].present?

if @order.save
UserMailer.confirm_order(@order).deliver
@order.user.accept_current_terms_of_service!(request.remote_ip)
flash["ignore_order_is_conversion"] = true #this is used to render the conversion tracking pixel - naudo feb.6.2012
flash_message(:notice, 'Your order was successfully created.')

if @order.invite_facebook_friends_to_reservation? && current_user.present? && current_user.is_a_facebook_user?
render(:invite_on_facebook) and return
end
render(:iframe_confirm, layout: 'minimal') and return if params[:iframe]
cookies['landing_tag'] = nil
redirect_to @order
else
# Reverse any preauth and/or subscription
@gateway_transaction.reverse_authorization_and_or_subscription if @gateway_transaction.present?

render(:iframe, layout: 'minimal') and return if params[:iframe]
render :new, layout: choose_layout
end
end

It’s not just the controllers
that get bloated, Views
get messed up, too...

Thicker than a five dollar
malt
= order_form.fields_for :reservation do |reservation_form|
= render "orders/reservation_hidden_fields", :reservation_form => reservation_form

- unless mobile_prefered?
= render "orders/restaurant_offer_details", :reservation_form => reservation_form

.psuedo-section
- if @order.restaurant.custom_logo_url.present?
%p.logo=image_tag(@order.restaurant.custom_logo_url)
%section#reservation_show
- if @ios_app
= render "orders/reservation_details"
= render "orders/reservation_datetime_form_new", :order_form => order_form, :reservation_form => reservation_form
- if mobile_prefered?
= render "orders/restaurant_offer_details", :reservation_form => reservation_form
= render "orders/reservation_info_form_new", :reservation_form => reservation_form
= hidden_field_tag :orderPage_receiptResponseURL, credit_user_account_orders_url
= hidden_field_tag :orderPage_declineResponseURL, credit_user_account_orders_url

- if @ios_app
#payment-info
- if @payment_required
- no_show_fee_amount = @restaurant.no_show_fee(@order.reservation)
- if no_show_fee_amount && no_show_fee_amount > 0.0
= render :partial => "shared/payment_details", :locals => { :countdown_minutes => nil, :payment_type =>
'noshow', :no_show_fee_amount => no_show_fee_amount }
- else
= render :partial => "shared/payment_details", :locals => { :countdown_minutes => nil, :payment_type =>
'purchase', :no_show_fee_amount => 0.0 }

= render "orders/reservation_submit", :reservation_form => reservation_form, :order_form => order_form

- if @layout != 'nometro' && @restaurant.metro.published?
.sidebar
= render "orders/reservation_faq"
= render :partial => "orders/loyalty_box", :locals => {:restaurant => @restaurant}
- if @order.has_offer?

Who will
maintain
and test
all this
logic?!?

Let’s Review...
Controllers

Model Views

GOLLY, that’s bad
news!
Controllers

Model Views

Presenter
s
Presenter

Controller

Model View

Represent “Current State of the
View”
Presenter

Controller

Model View

Invoicing!
Scripps needed a
way to preview
Invoices that were to
be sent to
Restaurants, as well
as view existing
invoices

Invoice
class InvoicePresenter Presenter
attr_accessor :reservation_transactions, :non_reservation_transactions, :transactions, :id, :date, :due_date, :account,
:reservation_transactions_total, :restaurant

def initialize(thing)
self.restaurant = thing.account.accountable
self.transactions = thing.transactions
self.date = thing.date
self.account = thing.account
self.reservation_transactions = thing.reservation_transactions
self.non_reservation_transactions = thing.non_reservation_transactions
if thing.is_a? Invoice
init_from_invoice(thing)
elsif thing.is_a? InvoicePreview
init_from_invoice_preview(thing)
else
raise ArgumentError.new("I don't know what to do with this thing.")
end
end
.
.
.
private

def init_from_invoice(invoice)
self.id = invoice.id
self.due_date = invoice.due_date || self.date.end_of_month + Invoice::INVOICE_DAYS_AFTER
end

def init_from_invoice_preview(preview)
self.id = "PREVIEW"
invoiced_on_date = self.date < Date.today ? Date.today : self.date
due_date = invoiced_on_date + Invoice::INVOICE_DAYS_AFTER
self.due_date = due_date
end
end

Invoice
Presenter
def render_performance_summary(context)
by_source = {}
total = 0
reservation_transactions.each do |txn|
unless txn.source.nil? # how does this happen?
by_source[txn.source.reservation_source.name] =
by_source.fetch(txn.source.reservation_source.name,0) + 1
total = total + 1
end
end
context.render partial: 'invoice_performance_summary',
locals: {total: total, by_source: by_source}
end

Invoice
def render_line_items(context)
Presenter
Yeah, it can still be kinda gross...
output = []

# First, the one time fees.
one_time_fee_total = 0.0
one_time_fees.each do |otf|
amount = otf[:unit_price] * otf[:quantity]
item = {unit_price: otf[:unit_price], quantity: otf[:quantity], description: otf[:description], discount: 0.00, amount: amount}
one_time_fee_total = one_time_fee_total + amount
output << context.render(partial: 'invoice_item', locals: {item: item})
end
unless one_time_fees.empty?
output << context.render(partial: 'invoice_total', locals: {total: one_time_fee_total, description: 'One Time Fees Subtotal', cssclass: 'sub-total'})
end

# Next, the reservation transactions
reservation_fee_total = 0.0
grouped_reservation_transactions.each do |txn|
amount = txn[:unit_price] * txn[:quantity]
item = {unit_price: txn[:unit_price], quantity: txn[:quantity], description: txn[:description], discount: 0.00, amount: amount}
reservation_fee_total = reservation_fee_total + amount
output << context.render(partial: 'invoice_item', locals: {item: item})
end
unless grouped_reservation_transactions.empty?
output << context.render(partial: 'invoice_total', locals: {total: reservation_fee_total, description: 'Reservation Fees Fees Subtotal', cssclass: 'sub-total'})
end

unless monthly_fee_cap_amount.blank? || monthly_fee_cap_amount.zero?
output << context.render(partial: 'invoice_total', locals: {total: "After Monthly Fee Cap - #{number_to_currency monthly_fee_cap_amount}", description: 'Balance at the
end of last period', cssclass: 'monthly-cap'})
end

# Other Totals
output << context.render(partial: 'invoice_total', locals: {total: balance_at_end_of_last_period, description: 'Balance at the end of last period', cssclass: 'sub-total'})
output << context.render(partial: 'invoice_total', locals: {total: last_payment_received_amount, description: "Payment Received - #{last_payment_received_on} - Thank
You", cssclass: 'sub-total'})
output << context.render(partial: 'invoice_total', locals: {total: sales_tax, description: 'Tax', cssclass: 'tax'})
output << context.render(partial: 'invoice_total', locals: {total: reservation_fee_total + one_time_fee_total + sales_tax, description: 'Total', cssclass: 'total'})
output.join
end

Invoice
%section
%h4#invoice-header
Invoice
%h4#ce-logo
Presenter
%img{:alt => 'CityEats', :src => '/assets/logo-cityeats-black.png'}
#invoice-summary
%h4 Invoice Summary:
%table
%tr

But the view is
%th
Invoice Id:
%td= @presenter.id

outta site!
%tr#invoice-date
%th Invoice Date:
%td= @presenter.date

%tr#due-date
%th Due Date:
%td= @presenter.due_date
%tr#amount-due
%th
Amount Due:
%td= number_to_currency(@presenter.amount_due)

#bill-to
%h4 Bill To:
= render partial: 'invoice_bill_to_address', locals: {name: @presenter.restaurant.name, address: @presenter.restaurant.address}

%h4 Remittance
%p The amount owing will automatically be charged to your credit card or debited from your bank account, according to the terms of your contract. <br /><em>If paying by check, please
include a copy of this statement.</em>

%h4 Fee Summary
%table#fee-summary
%tr

Gosh, no references to
%th Description
%th.quantity Quantity
%th.unit-price Unit Price
%th.discount Discount

models anywhere!
%th.amount Amount
= raw @presenter.render_line_items(self)

%h4 Performance Summary
= raw @presenter.render_performance_summary(self)

= javascript_include_tag "invoicing"

...and the controller is tiny, too!

def show
invoice = Invoice.ﬁnd(params[:id])
@presenter = InvoicePresenter.new(invoice)
end

def new
account = @restaurant.account
invoice_date = @restaurant.next_invoice_date
@presenter = InvoicePresenter.new(InvoicePreview.new(account, invoice_date))
end

Have you ever written
a good view test?

Have you ever written
a good view test?
No, seriously. Be
Honest.

Can’t I just do all this with
Helpers?

Helpers don’t have
State

Exhibitor Pattern
Uses “Decorator Pattern” to extend an
existing model
Implements Decorator Pattern using
Ruby’s SimpleDelegator class

Decorator Pattern?
Delegate Decorator

Hey look, it’s UML! I read
about this in a Computer
Science Archaeology Book
once!

Decorator Pattern?
Delegate Decorator
+jumpFromSpaceBalloon

Decorator Pattern?
Delegate Decorator
+jumpFromSpaceBalloon +jumpFromSpaceBalloon
+drinkRedBull

Decorator Pattern?
Delegate SimpleDelegator
+jumpFromSpaceBalloon +initializer(thing: Delegate)
+drinkRedBull

Gosh, Ruby
sure is spiffy!

Decorator Pattern?
SimpleDelegator

Model Exhibitor
+initializer(a_model: Model)
+render_body(context:View)

Exhibitor Pattern
Uses “Decorator Pattern” to extend an
existing model
Implements Decorator Pattern using
Ruby’s SimpleDelegator class
# exhibits/text_post_exhibit.rb
require 'delegate'
class TextPostExhibit < SimpleDelegator
def initialize(model, context)
@context = context
super(model)
end

def render_body
@context.render(partial: "/posts/text_body", locals: {post: self})
end
end

some People in the rails
Community conﬂate these
two notions (exhibitor vs.
presenter)

But now you’re smarter
than all of them!

FURTHER Reading
http://blog.jayﬁelds.com/2007/03/rails-presenter-pattern.html

http://broadcastingadam.com/2011/06/present_yourself/

http://railsvideos.net/railsconf-2012-presenters-and-decorators-a-co

FURTHER Reading
http://blog.jayﬁelds.com/2007/03/rails-presenter-pattern.html

Simple one, does some similar stuff w/ delegation like Avdi without using
SimpleDelagator

http://broadcastingadam.com/2011/06/present_yourself/

Does some neat stuff with memoization

http://railsvideos.net/railsconf-2012-presenters-and-decorators-a-co
Very Good RailsConf 2012 Presentation by Mike Moore. Uses
ActiveDecorator to implement a form of Exhibitor

Quest ions?

Retro Clip Art Provided By Tack-o-Rama
http://tackorama.net

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