directly create billing expense from volunteer view

app/models/billing_expense.rb

 class BillingExpense < ApplicationRecord
   include FullBankDetails
 
-  before_validation :compute_amount
+  before_validation :auto_set_amount
+
   belongs_to :volunteer
   belongs_to :user, -> { with_deleted }
   has_many :hours
@@ -25,6 +26,10 @@ class BillingExpense < ApplicationRecord
     super(compute_amount)
   end
 
+  def auto_set_amount
+    self.amount = nil
+  end
+
   def compute_amount
     hour_count = id ? hours_sum : volunteer.billable_hours_sum
     if hour_count > 50

app/views/billing_expenses/index.html.slim

@@ -30,7 +30,9 @@ h1= t_title(:index, BillingExpense)
               td= link_to t_action(:destroy), volunteer_billing_expense_path(@volunteer, record), confirm_deleting(record)
 .row
   .col-xs-12
-= form_navigation_btn :new
+    = simple_form_for [@volunteer, BillingExpense.new] do |f|
+      = f.hidden_field :volunteer_id, value: @volunteer.id
+      = f.button :submits
 .row
   .col-xs-12
     = button_link t('back'), @volunteer

app/views/volunteers/show.html.slim

@@ -10,8 +10,12 @@ nav.navbar.section-navigation
         - if @volunteer.seeking_clients?
           li = button_link t_title(:new, Assignment), new_assignment_path(volunteer_id: @volunteer)
         - if @volunteer.assignments.any?
-          li = button_link t_title(:new, BillingExpense), new_volunteer_billing_expense_path(@volunteer)
-          li = button_link t_title(:index, BillingExpense), volunteer_billing_expenses_path(@volunteer)
+          li
+            = simple_form_for [@volunteer, BillingExpense.new] do |f|
+              = f.hidden_field :volunteer_id, value: @volunteer.id
+              = f.button :submits
+          - if @volunteer.billing_expenses.any?
+            li = button_link t_title(:index, BillingExpense), volunteer_billing_expenses_path(@volunteer)
         - if @volunteer.assignments?
           li= button_link t('.new_certificate'), new_volunteer_certificate_path(@volunteer)
           - if @volunteer.certificates.size == 1