How can I move calculations in View to Model? - ruby-on-rails

Question

I´m very new to ROR and I have stumbled up on a problem. I believe it´s a newbie problem, but I´m not sure if it´s. I´m building this app were users should be able to enter the amount of paper use in their business and from there the app calculates their eco footprint so to say.
at login the user enters their staff number. The staff number is used to divide with paper_weight etc. ( see in view example).
I know it basically works the way it is now, but I´m aware of this is not the best practice.
I also wanted to move the div containing the running totals to application.html.erb but I can´t do that since my calculations are in the View but not in the Model.
here is a link to the github repo https://github.com/DadiHall/SprettaEMS1.5
Are there any other ways to do this? Can someone please advise me?
my index.html.erb view
<div class="row">
<div class="col-md-10 ">
<h1>Pappírsnotkun</h1>
<table class=" well table table-hover">
<thead>
<tr>
<th>Dags</th>
<th>Tegund</th>
<th>Þyngd</th>
<th>Kostnaður</th>
<th>Þar af umhvm. pappír</th>
<th>Pappírs magn m.v. Stöðugildi</th>
<th>Hl.f. Umhvm. Pappírs</th>
<th>Fjöldi trjáa m.v. magn pappírs</th>
</tr>
</thead>
<tbody>
<% paper_total_cost = 0 %>
<% paper_total_trees = 0 %>
<% paper_total_staff_ratio = 0 %>
<% #papers.each do |paper| %>
<tr>
<td><%= paper.date.strftime("%Y/%m/%d") %></td>
<td><%= paper.paper_type %></td>
<td><%= paper.paper_weight %> -kg.</td>
<td><%= paper.paper_cost %> -kr.</td>
<td><%= paper.env_paper_weight %> -kg.</td>
<td><%= (paper.paper_weight.to_i / current_user.staff) %> kg/stöðugildi </td>
<td><%= (( paper.env_paper_weight / paper.paper_weight)* 100) %>%</td>
<td><%= (( paper.paper_weight.to_f/1000)*15) %></td>
<td><%= link_to 'Sýna', paper, class: 'btn btn-xs btn-info' %></td>
<td><%= link_to 'Uppfæra', edit_paper_path(paper), class: 'btn btn-xs btn-warning' %></td>
<td><%= link_to 'Eyða', paper, method: :delete, class: 'btn btn-xs btn-danger', data: { confirm: 'Are you sure?' } %></td>
<% paper_total_cost = paper_total_cost + (paper.paper_cost.to_i) %>
<% paper_total_trees = paper_total_trees + (( paper.paper_weight.to_f/1000)*15) %>
<% paper_total_staff_ratio = paper_total_staff_ratio + (paper.paper_weight.to_i / current_user.staff) %>
</tr>
<% end %>
</tbody>
</table>
</div>
<div class="row">
<div class=" col-md-2 panel panel-default pull-right" >
<div class="panel panel-heading ">
<h5 class="user-name">User: <% if current_user && current_user %>
<%= current_user.name %>,
Staff: <%= current_user.staff %>
<% end %>
</h5>
</div>
<div class="panel-body">
<h6 class="pull-right">Pappír Kostnaður Samtals:<%= number_with_precision(paper_total_cost.to_f, precision: 2) %> kr </h6><br>
<h6 class="pull-right">Fjöldi Trjáa vegna Pappírs notkunar:<%= number_with_precision(paper_total_trees.to_f, precision: 2) %> Tré </h6><br>
<h6 class="pull-right">Magn Pappírs f. hvert stöðugildi:<%= number_with_precision(paper_total_staff_ratio.to_f, precision: 2) %> Kg </h6>
</div>
</div>
</div>
<%= link_to 'New Paper', new_paper_path %>
My papers_controller.rb
class PapersController < ApplicationController
before_action :set_paper, only: [:edit, :update, :show, :destroy]
def index
#papers = Paper.all
end
def create
#paper = Paper.new(paper_params)
if #paper.save
flash[:success] = "Messages sent."
redirect_to paper_path(#paper)
else
flash[:danger] = "Error occured, message has not been sent."
redirect_to new_paper_path
end
end
def new
#paper = Paper.new
end
def edit
end
def show
end
def update
if #paper.update(paper_params)
flash[:success] = "Line was successfully updated"
redirect_to papers_path(#paper)
else
render 'edit'
end
end
def destroy
#paper.destroy
flash[:danger] = "Line was successfully destroyed"
redirect_to papers_path
end
private
def set_paper
#paper = Paper.find(params[:id])
end
def paper_params
params.require(:paper).permit(:paper_type, :date, :paper_weight, :paper_cost, :env_paper_weight)
end
end
my paper.rb Model
class Paper < ActiveRecord::Base
has_many :users
end

Answer 1

You can move the calculations into the model by defining functions in the model.
The first calculation uses current_user, which will not be in the model by default, so that'll have to be a parameter. The other two are just using paper's attributes; pardon my poor naming, I'm not clear what the second two metrics are.
class Paper
has_many :users
def paper_weight_per_capita(current_user)
paper_weight.to_i / current_user.staff
end
def paper_weight_metric1
( env_paper_weight / paper_weight)* 100)
end
def paper_weight_metric2
(( paper_weight.to_f/1000)*15)
end
end
And in your view
<%= paper.paper_weight_per_capita(current_user) %>
<%= paper.paper_weight_metric1 %>
If you want the running total in your layout then you'll need to load the paper objects on every page. You can do this with an application_controller before_action, though some folks don't like this approach and here, but I think it is a reasonable way for you now.
class ApplicationController < ActionController::Base
before_action :load_running_totals
def load_running_totals
# method 1. Similar to how the calculation is done in the view.
# #paper_weight_per_capita = Papers.all.map(&:paper_weight_per_capita, current_user).reduce(&:+)
# method 2. does the summation in the database without having to load all the records into ruby. (weight needs to be a number in the db.)
#paper_weight_per_capita = Papers.sum(:weight) / current_user.staff
end
end
Now in any view (including your layout):
<%= #paper_weight_per_capita %>