Sort the balance column in ruby on rails 6 - ruby

Question

I am trying to calculate and sort the balance column in the table as per the image shown below;
For that, I used #mexpenses = #mexpenses.sort { |e| e.balance } for sorting as it results in undesired results so I commented out in the code below.
I would like to achieve the results as shown in the rightmost BALANCE column in the above image.
Everything in the table from the Date column to the Debit column is shown as desired only the Balance column is causing the issue.
I would like to get the latest record at the top of the statement with the appropriate balance.
Note: No balance column is in the database.
mexpenses_controller.rb
def index
#mexpenses = Mexpense.order('date DESC')
balance = 763.87
#mexpenses.each do |e|
balance += e.credit.to_f - e.debit.to_f
e.balance = balance
end
# #mexpenses = #mexpenses.sort { |e| e.balance }
respond_to do |format|
format.html
format.xls
end
end
Mexpense.rb
class Mexpense < ActiveRecord::Base
validates :particulars, presence: true
validates :date, presence: true
attr_accessor :balance
after_initialize :init
def init
self.balance = 0
end
end
index.html.erb
<div class="row">
<div class="col-md-8 col-md-offset-2">
<div class="table-responsive myTable">
<table class="table listing text-center">
<tr class="tr-head">
<td>Date</td>
<td>Particulars</td>
<td>Credit</td>
<td>Debit</td>
<td>Balance</td>
</tr>
<tr>
<td></td>
</tr>
<% #mexpenses.each do |mexpense| %>
<tr class="tr-<%= cycle('odd', 'even') %>">
<td class="col-1"><%= mexpense.date.strftime('%d/%m/%Y') %></td>
<td class="col-1" style="width: 50%;"><%= link_to mexpense, mexpense %></td>
<td class="col-1 neg" style="width: 10%;"><%= number_with_precision(mexpense.credit, :delimiter => ",", :precision => 2) %></td>
<td class="col-1 pos" style="width: 10%;"><%= number_with_precision(mexpense.debit, :delimiter => ",", :precision => 2) %></td>
<td><%= number_with_precision(mexpense.balance, :delimiter => ",", :precision => 2) %></td>
</tr>
<% end %>
</table>
</div>
</div>
</div>
20210213052730_create_mexpenses.rb
class CreateMexpenses < ActiveRecord::Migration
def change
create_table :mexpenses do |t|
t.date :date
t.string :particulars
t.decimal :debit
t.decimal :credit
t.timestamps null: false
end
end
end
Any suggestions are most welcome.
Thank you in advance.

Answer 1

I strongly recommend to store the balance column in the database. Each time debit or credit is changed, the balance column will be updated.
store MONEY as integer!!!! This avoids floating point rounding errors.
console:
rails g migration add_balance_to_mexpenses balance:integer
migration:
add_column :mexpenses, :balance, :integer, default: 0, null: false
mexpence.rb - update balance column whenever a `mexpence is changed
after_save do
update :balance, credit - debit
end
Now you can easily order by balance that is a separate field in your database. Something like:
#mexpenses = Mexpense.order(date: :desc, balance: :desc)