Sum last values of each column issue

Question

I did an app to sum the last values of each column but i'm getting the total sum

Here my tables

|policies|
 |id|  |num_policy|
   1      1234
   2      4567 

|insurances|
 |id|  |id_policy| |net_insurance| 
  1          1      4000
  2          1      6000
  3          2      3000 
  4          2      7000 

I'm trying to do in excel

|id|   |num_policy|   |net_insurance|
 1        1234           4000
 2        4567           7000

          sum =        11000   

This is my controller

class PolicyController < ApplicationController
    def generate_print

      @policies= Policy.find(:all)
      @dolar = Insurance.sum(:net_insurance)

      respond_to do |format|
         format.html
         format.xls { send_data render_to_string(:partial=>"report_by_sum"),  :filename => "Report_#{Date.today}.xls" }
      end

    end
end

This is my model

class Policy < ActiveRecord::Base
  has_many :insurances
end

class Insurance < ActiveRecord::Base
  belongs_to :policy
  has_many :insurance_financing_details
end

This is my view showing the last insurance of each policy

<% @policies.each do |policy| %>
    <%= policy.num_policy %>
    <% policy.insurances.last(1).each do |insurance| %>          
        <%= insurance.net_insurance %>
    <% end %>
<% end %>

<%= link_to "Export Excel",{:controller=>"policy",:action=>"generate_print" ,:format=>"xls"}  %>

This is my partial view that i'm trying to sum it should show "11000" but i got "20000"

 #   _report_by_sum.erb
<%= @dolar %>

Someone can help me with this issue please?

I will really appreciate help

Answer 1

This line

@dolar = Insurance.sum(:net_insurance)

Calculates the sum of all insurance entries, i.e. 4000 + 6000 + 3000 + 7000.

You have to fetch the last insurance for each policy instead:

@dolar = @policies.to_a.sum { |policy| policy.insurances.last.net_insurance }