Fix RedundantPresenceValidationOnBelongs on two files

- presence: true is redundant since Rails 5.0 BUT applies
       with new default config of
       belongs_to_required_by_default to true.
       Lots of files with belongs_to_required_by_default = false
       (backward compatibility).
       So: deleting this setting implies to adding optional: true
     - added 'NOT NULL' constraints so model constraints match
       with contraints on DB tables.
     - corresponding migration files to match AR Models &
       DB tables
     - rake tasks to check corrupt data (ie: NULL/nil in id fields)
     - updated the todo

.rubocop_todo.yml

@@ -650,16 +650,14 @@ Rails/RedundantActiveRecordAllMethod:
     - 'app/models/spree/variant.rb'
     - 'spec/system/admin/product_import_spec.rb'
 
-# Offense count: 9
+# Offense count: 7
 # This cop supports unsafe autocorrection (--autocorrect-all).
 Rails/RedundantPresenceValidationOnBelongsTo:
   Exclude:
     - 'app/models/spree/line_item.rb'
     - 'app/models/spree/order.rb'
-    - 'app/models/spree/tax_rate.rb'
     - 'app/models/subscription_line_item.rb'
     - 'app/models/tag_rule.rb'
-    - 'app/models/variant_override.rb'
 
 # Offense count: 1
 # This cop supports unsafe autocorrection (--autocorrect-all).

app/models/spree/tax_rate.rb

@@ -14,17 +14,14 @@ end
 
 module Spree
   class TaxRate < ApplicationRecord
-    self.belongs_to_required_by_default = false
-
     acts_as_paranoid
     include CalculatedAdjustments
 
-    belongs_to :zone, class_name: "Spree::Zone", inverse_of: :tax_rates
+    belongs_to :zone, class_name: "Spree::Zone", inverse_of: :tax_rates, optional: true
     belongs_to :tax_category, class_name: "Spree::TaxCategory", inverse_of: :tax_rates
     has_many :adjustments, as: :originator, dependent: nil
 
     validates :amount, presence: true, numericality: true
-    validates :tax_category, presence: true
     validates_with DefaultTaxZoneValidator
 
     scope :by_zone, ->(zone) { where(zone_id: zone) }

app/models/variant_override.rb

@@ -6,15 +6,11 @@ class VariantOverride < ApplicationRecord
   extend Spree::LocalizedNumber
   include StockSettingsOverrideValidation
 
-  self.belongs_to_required_by_default = false
-
   acts_as_taggable
 
   belongs_to :hub, class_name: 'Enterprise'
   belongs_to :variant, class_name: 'Spree::Variant'
 
-  validates :hub, presence: true
-  validates :variant, presence: true
   # Default stock can be nil, indicating stock should not be reset or zero, meaning reset to zero.
   # Need to ensure this can be set by the user.
   validates :default_stock, numericality: { greater_than_or_equal_to: 0 }, allow_nil: true

db/migrate/20240517121235_require_tax_category_on_tax_rate.rb

@@ -0,0 +1,5 @@
+class RequireTaxCategoryOnTaxRate < ActiveRecord::Migration[7.0]
+  def change
+    change_column_null :spree_tax_rates, :tax_category_id, false
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.0].define(version: 2024_05_01_075735) do
+ActiveRecord::Schema[7.0].define(version: 2024_05_17_121235) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_stat_statements"
   enable_extension "plpgsql"
@@ -871,7 +871,7 @@ ActiveRecord::Schema[7.0].define(version: 2024_05_01_075735) do
   create_table "spree_tax_rates", id: :serial, force: :cascade do |t|
     t.decimal "amount", precision: 8, scale: 5
     t.integer "zone_id"
-    t.integer "tax_category_id"
+    t.integer "tax_category_id", null: false
     t.datetime "created_at", precision: nil, null: false
     t.datetime "updated_at", precision: nil, null: false
     t.boolean "included_in_price", default: false

lib/tasks/data/check_missing_required_ids_in_tax_rates.rake

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+namespace :ofn do
+  namespace :data do
+    desc 'Checking missing required ids in Spree::TaxRate'
+    task check_missing_required_missing_ids_in_spree_tax_rates: :environment do
+      puts 'Checking for null tax_category_id'
+      ids = Spree::TaxRate.where(tax_category_id: nil).pluck(:id)
+
+      if ids.empty?
+        puts 'No NULL tax_category_id found in spree_tax_rates'
+      else
+        puts 'NULL tax_category_ids s have been found in spree_tax_rates:'
+        print ids
+      end
+    end
+  end
+end