add mortgage to derived variables so that mortgage value is set to 0 if a mortgage is not being used in the sale

app/models/derived_variables/sales_log_variables.rb

@@ -15,6 +15,9 @@ module DerivedVariables::SalesLogVariables
     if mscharge_known.present? && mscharge_known.zero?
       self.mscharge = 0
     end
+    if mortgage_not_used?
+      self.mortgage = 0
+    end
     self.pcode1, self.pcode2 = postcode_full.split(" ") if postcode_full.present?
     self.totchild = total_child
     self.totadult = total_adult + total_elder

app/models/sales_log.rb

@@ -28,7 +28,6 @@ class SalesLog < Log
   before_validation :process_previous_postcode_changes!, if: :ppostcode_full_changed?
   before_validation :reset_location_fields!, unless: :postcode_known?
   before_validation :reset_previous_location_fields!, unless: :previous_postcode_known?
-  before_validation :set_mortgage_value_zero, if: :mortgage_not_used?
   before_validation :set_derived_fields!
 
   scope :filter_by_year, ->(year) { where(saledate: Time.zone.local(year.to_i, 4, 1)...Time.zone.local(year.to_i + 1, 4, 1)) }
@@ -187,10 +186,6 @@ class SalesLog < Log
     mortgageused == 2
   end
 
-  def set_mortgage_value_zero
-    self.mortgage = 0
-  end
-
   def process_postcode_changes!
     self.postcode_full = upcase_and_remove_whitespace(postcode_full)
     process_postcode(postcode_full, "pcodenk", "is_la_inferred", "la")

spec/models/sales_log_spec.rb

@@ -140,6 +140,12 @@ RSpec.describe SalesLog, type: :model do
       expect(record_from_db["pcode1"]).to eq("W6")
       expect(record_from_db["pcode2"]).to eq("0SP")
     end
+
+    it "derives a mortgage value of 0 when mortgage is not used" do
+      sales_log.update!(mortgageused: 2)
+      record_from_db = ActiveRecord::Base.connection.execute("select mortgage from sales_logs where id=#{sales_log.id}").to_a[0]
+      expect(record_from_db["mortgage"]).to eq(0.0)
+    end
   end
 
   context "when saving addresses" do