如何在模型中添加额外属性以将计算移出视图？

Question

对于以下RubyOnRails代码，有没有办法将“利润”计算移出View并进入模型..所以可能有一个名为 total_income 和 total_expense <的属性/强>

型号 - transaction.rb

class Transaction < ActiveRecord::Base
  attr_accessible :name, :amount, :category
  scope :incomes,  :conditions => { :category => 'Income'  }
  scope :expenses, :conditions => { :category => 'Expense' }
end

控制器 - transactions_controller.rb

class TransactionsController < ApplicationController

  def index
    @incomes  = Transaction.incomes
    @expenses = Transaction.expenses
    @transaction = Transaction.new
  end

查看 - index.html.erb

<pre>
<strong>Income</strong>
  <% @incomes.each do |income| %>
  <%= income.name %>  -  <%= number_to_currency((income.amount.nil? ? 0 : income.amount)) %>
  <% end %>
  <strong>Subtotal:</strong> <%= number_to_currency(@income_total = @incomes.sum(:amount)) %>

<strong>Expenses</strong>
  <% @expenses.each do |expense| %>
  <%= expense.name %>  -  <%= number_to_currency((expense.amount.nil? ? 0 : expense.amount)) %>
  <% end %>
  <strong>Subtotal:</strong> <%= number_to_currency(@expenses_total = @expenses.sum(:amount)) %>

<strong>Profit: <%= number_to_currency(@income_total - @expenses_total) %></strong>
</pre>

Answer 1

对于最基本的更改，您只需将类方法添加到Transaction

即可

class Transaction < ActiveRecord::Base
  attr_accessible :name, :amount, :category
  scope :incomes,  :conditions => { :category => 'Income'  }
  scope :expenses, :conditions => { :category => 'Expense' }

  def self.income_total
    incomes.sum :amount
  end

  def self.expenses_total
    expenses.sum :amount
  end

end

class TransactionsController < ApplicationController

  def index
    @incomes  = Transaction.incomes
    @expenses = Transaction.expenses
    @income_total = Transaction.income_total
    @expenses_total = Transaction.expenses_total
    @transaction = Transaction.new
  end

Answer 2

这些天我更喜欢将这些多个相互依赖的实例变量包装到一个新的演示者类中，类似于（未经测试）：

class TransactionPresenter

  attr_reader :income_total, :expenses_total

  def initialize
    @incomes = Transaction.incomes
    @expenses = Transaction.expenses
  end

  def each_income(&block)
    @incomes.each(&block)
  end

  def each_expense(&block)
    @incomes.each(&block)
  end

  def income_total
    @income_total ||= number_to_currency(@incomes.sum(&:amount))
  end

  def expenses_total
    @expenses_total ||= number_to_currency(@expenses.sum(&:amount))
  end

  def name_and_amount(income_or_expense)
    "#{income_or_expense.name} - #{number_to_currency((income.amount.nil? ? 0 : income.amount))}"
  end

  def profit
    number_to_currency(income_total - expenses_total)
  end

end

# controller

def index
  @presenter = TransactionPresenter.new
end

# view

<pre>
<strong>Income</strong>
  <% @presenter.each_income do |income| %>
    <%= @presenter.name_and_amount %>
  <% end %>
  <strong>Subtotal:</strong> <%= @presenter.income_total %>

<strong>Expenses</strong>
  <% @presenter.each_expense do |expense| %>
    <%= @presenter.name_and_amount %>
  <% end %>
  <strong>Subtotal:</strong> <%= @presenter.expenses_total %>

<strong>Profit: <%= @presenter.profit %></strong>
</pre>