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
   

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3. What is a presenter?
   

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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
   

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5. View Models
   Object-Orientated helpers
   

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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
   

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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)
   

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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)
   

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9. Skinny Everything
   The Single Responsibility Principle
   Single Responsibility Principle
   http://en.wikipedia.org/wiki/Single_responsibility_principle
   

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10. PROS
    

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11. Fewer conditionals
    

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12. Fewer or Simpler
    Callbacks
    

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13. Easier Testing
    

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14. CONS
    

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15. Typecasting
    

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16. More Objects
    

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17. Writing Java
    

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19. EFG
    alphagov/EFG
    https://github.com/alphagov/EFG
    d909af...008444
    

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21. InvoicesController
    Invoices
    

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22. InvoicesController
    Invoices InvoiceReceived
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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)
    

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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
    

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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
    

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33. Notable mentions
    Focused Controller
    https://github.com/jonleighton/focused_controller
    Virtus
    https://github.com/solnic/virtus
    

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34. new bamboo
    

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