Presenters – Take II

In 2007, I gave a talk about using Presenters with Rails. Here I re-visit the topic drawing on experiences developing an application for the UK Government.

Transcript

1. Presenters Take II
3. What is a presenter?
4. All THE Things 7 Patterns to Refactor Fat ActiveRecord Models http://blog.codeclimate.com/blog/2012/10/17/7-ways-to-decompose-fat-activerecord-models/ 1. Form Objects 2. Service Objects 3. View Models
5. View Models Object-Orientated helpers
6. class PersonPresenter def initialize(person) @person = person end def full_name "#{person.first_name} #{person.last_name}" end def date_of_birth person.date_of_birth.to_s(:full) end private attr_reader :person end
7. WHERE DID PRESENTERs COme From? Rails: Presenter Pattern http://blog.jayfields.com/2007/03/rails-presenter-pattern.html “Presenter was inspired by the various GUI patterns documented by Martin Fowler. The Presenter pattern addresses bloated controllers and views containing logic in concert by creating a class representation of the state of the view. An architecture that uses the Presenter pattern provides view specific data as attributes of an instance of the Presenter. The Presenter's state is an aggregation of model and user entered data.” – Jay Fields (2007)
8. Skinny Controller, Fat Model Skinny Controller, Fat Model http://weblog.jamisbuck.org/2006/10/18/skinny-controller-fat-model “Be aggressive! Try to keep your controller actions and views as slim as possible. A one-line action is a thing of wonder, as is a template that is mostly HTML. It is also much more maintainable than a view that is full of assignment statements and chained method calls.” – Jamis Buck (2007)
9. Skinny Everything The Single Responsibility Principle Single Responsibility Principle http://en.wikipedia.org/wiki/Single_responsibility_principle
10. PROS
11. Fewer conditionals
12. Fewer or Simpler Callbacks
13. Easier Testing
14. CONS
15. Typecasting
16. More Objects
17. Writing Java
19. EFG alphagov/EFG https://github.com/alphagov/EFG d909af...008444
21. InvoicesController Invoices
22. InvoicesController Invoices InvoiceReceived
23. require 'active_model/model' class InvoiceReceived PERIOD_COVERED_QUARTERS = Invoice::PERIOD_COVERED_QUARTERS include ActiveModel::Model include ActiveModel::MassAssignmentSecurity attr_reader :invoice attr_accessor :lender, :reference, :period_covered_quarter, :period_covered_year, :received_on, :creator attr_accessible :lender_id, :reference, :period_covered_quarter, :period_covered_year, :received_on, :loans_attributes validates :lender_id, presence: true validates :reference, presence: true validates :received_on, presence: true validates :period_covered_quarter, presence: true, inclusion: PERIOD_COVERED_QUARTERS validates :period_covered_year, presence: true, format: /\A(\d{4})\Z/ validates_presence_of :creator, strict: true, on: :save validate(on: :save) do |invoice| if loans.none? {|loan| loan.settled? } errors.add(:base, 'No loans were selected.') end end def self.name Invoice.name end def lender_id lender && lender.id end
24. require 'active_model/model' class InvoiceReceived PERIOD_COVERED_QUARTERS = Invoice::PERIOD_COVERED_QUARTERS include ActiveModel::Model include ActiveModel::MassAssignmentSecurity attr_reader :invoice attr_accessor :lender, :reference, :period_covered_quarter, :period_covered_year, :received_on, :creator attr_accessible :lender_id, :reference, :period_covered_quarter, :period_covered_year, :received_on, :loans_attributes validates :lender_id, presence: true validates :reference, presence: true validates :received_on, presence: true validates :period_covered_quarter, presence: true, inclusion: PERIOD_COVERED_QUARTERS validates :period_covered_year, presence: true, format: /\A(\d{4})\Z/ validates_presence_of :creator, strict: true, on: :save validate(on: :save) do |invoice| if loans.none? {|loan| loan.settled? } errors.add(:base, 'No loans were selected.') end end def self.name Invoice.name end def lender_id lender && lender.id end
25. require 'active_model/model' class InvoiceReceived PERIOD_COVERED_QUARTERS = Invoice::PERIOD_COVERED_QUARTERS include ActiveModel::Model include ActiveModel::MassAssignmentSecurity attr_reader :invoice attr_accessor :lender, :reference, :period_covered_quarter, :period_covered_year, :received_on, :creator attr_accessible :lender_id, :reference, :period_covered_quarter, :period_covered_year, :received_on, :loans_attributes validates :lender_id, presence: true validates :reference, presence: true validates :received_on, presence: true validates :period_covered_quarter, presence: true, inclusion: PERIOD_COVERED_QUARTERS validates :period_covered_year, presence: true, format: /\A(\d{4})\Z/ validates_presence_of :creator, strict: true, on: :save validate(on: :save) do |invoice| if loans.none? {|loan| loan.settled? } errors.add(:base, 'No loans were selected.') end end def self.name Invoice.name end def lender_id lender && lender.id end
26. require 'active_model/model' class InvoiceReceived PERIOD_COVERED_QUARTERS = Invoice::PERIOD_COVERED_QUARTERS include ActiveModel::Model include ActiveModel::MassAssignmentSecurity attr_reader :invoice attr_accessor :lender, :reference, :period_covered_quarter, :period_covered_year, :received_on, :creator attr_accessible :lender_id, :reference, :period_covered_quarter, :period_covered_year, :received_on, :loans_attributes validates :lender_id, presence: true validates :reference, presence: true validates :received_on, presence: true validates :period_covered_quarter, presence: true, inclusion: PERIOD_COVERED_QUARTERS validates :period_covered_year, presence: true, format: /\A(\d{4})\Z/ validates_presence_of :creator, strict: true, on: :save validate(on: :save) do |invoice| if loans.none? {|loan| loan.settled? } errors.add(:base, 'No loans were selected.') end end def self.name Invoice.name end def lender_id lender && lender.id end
27. def lender_id lender && lender.id end def lender_id=(id) self.lender = Lender.find_by_id(id) end def received_on=(value) @received_on = QuickDateFormatter.parse(value) end def loans @loans ||= lender.loans.demanded.includes(:lending_limit).map {|loan| SettleLoan.new(loan) } end def loans_attributes=(values) values.each do |_, attributes| loan = loans_by_id[attributes['id'].to_i] loan.settled = (attributes['settled'] == '1') loan.settled_amount = attributes['settled_amount'] end end def attributes=(values) sanitize_for_mass_assignment(values).each do |attr, value| public_send("#{attr}=", value) end end def save # This is intentionally eager. We want to run all of the validations. return false if invalid?(:details) | invalid?(:save) | settled_loans.map(&:invalid?).any? ActiveRecord::Base.transaction do
28. def lender_id lender && lender.id end def lender_id=(id) self.lender = Lender.find_by_id(id) end def received_on=(value) @received_on = QuickDateFormatter.parse(value) end def loans @loans ||= lender.loans.demanded.includes(:lending_limit).map {|loan| SettleLoan.new(loan) } end def loans_attributes=(values) values.each do |_, attributes| loan = loans_by_id[attributes['id'].to_i] loan.settled = (attributes['settled'] == '1') loan.settled_amount = attributes['settled_amount'] end end def attributes=(values) sanitize_for_mass_assignment(values).each do |attr, value| public_send("#{attr}=", value) end end def save # This is intentionally eager. We want to run all of the validations. return false if invalid?(:details) | invalid?(:save) | settled_loans.map(&:invalid?).any? ActiveRecord::Base.transaction do
29. def lender_id lender && lender.id end def lender_id=(id) self.lender = Lender.find_by_id(id) end def received_on=(value) @received_on = QuickDateFormatter.parse(value) end def loans @loans ||= lender.loans.demanded.includes(:lending_limit).map {|loan| SettleLoan.new(loan) } end def loans_attributes=(values) values.each do |_, attributes| loan = loans_by_id[attributes['id'].to_i] loan.settled = (attributes['settled'] == '1') loan.settled_amount = attributes['settled_amount'] end end def attributes=(values) sanitize_for_mass_assignment(values).each do |attr, value| public_send("#{attr}=", value) end end def save # This is intentionally eager. We want to run all of the validations. return false if invalid?(:details) | invalid?(:save) | settled_loans.map(&:invalid?).any? ActiveRecord::Base.transaction do
30. def save # This is intentionally eager. We want to run all of the validations. return false if invalid?(:details) | invalid?(:save) | settled_loans.map(&:invalid?).any? ActiveRecord::Base.transaction do create_invoice! settle_loans! end true rescue ActiveRecord::RecordInvalid false end def grouped_loans @groups ||= LoanGroupSet.filter(loans) end private attr_writer :invoice def create_invoice! self.invoice = Invoice.create! do |invoice| invoice.lender = self.lender invoice.reference = self.reference invoice.period_covered_quarter = self.period_covered_quarter invoice.period_covered_year = self.period_covered_year invoice.received_on = self.received_on invoice.created_by = self.creator end end def settle_loans! settled_loans.each do |loan| loan.settle!(invoice, self.creator)
31. def create_invoice! self.invoice = Invoice.create! do |invoice| invoice.lender = self.lender invoice.reference = self.reference invoice.period_covered_quarter = self.period_covered_quarter invoice.period_covered_year = self.period_covered_year invoice.received_on = self.received_on invoice.created_by = self.creator end end def settle_loans! settled_loans.each do |loan| loan.settle!(invoice, self.creator) end end def loans_by_id @loans_by_id ||= loans.index_by(&:id) end def settled_loans loans.select(&:settled?) end end
32. def create_invoice! self.invoice = Invoice.create! do |invoice| invoice.lender = self.lender invoice.reference = self.reference invoice.period_covered_quarter = self.period_covered_quarter invoice.period_covered_year = self.period_covered_year invoice.received_on = self.received_on invoice.created_by = self.creator end end def settle_loans! settled_loans.each do |loan| loan.settle!(invoice, self.creator) end end def loans_by_id @loans_by_id ||= loans.index_by(&:id) end def settled_loans loans.select(&:settled?) end end
33. Notable mentions Focused Controller https://github.com/jonleighton/focused_controller Virtus https://github.com/solnic/virtus
34. new bamboo