Question

For the following RubyOnRails code, is there a way to move the “profit” calculation out of the View and into the Model.. so there’s maybe an attribute called total_income and total_expense?

Model – transaction.rb

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

Controller – transactions_controller.rb

class TransactionsController < ApplicationController

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

View – 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

For the most basic change you could just add class methods to Transaction

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