Fix RedundantPresenceValidationOnBelongs on some files (part VI)

- 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)
   (previous commit)
 - updated the todo

.rubocop_todo.yml

@@ -642,11 +642,10 @@ Rails/RedundantActiveRecordAllMethod:
     - 'app/models/spree/variant.rb'
     - 'spec/system/admin/product_import_spec.rb'
 
-# Offense count: 4
+# Offense count: 3
 # This cop supports unsafe autocorrection (--autocorrect-all).
 Rails/RedundantPresenceValidationOnBelongsTo:
   Exclude:
-    - 'app/models/spree/line_item.rb'
     - 'app/models/spree/order.rb'
 
 # Offense count: 1

app/models/spree/line_item.rb

@@ -7,8 +7,6 @@ module Spree
     include VariantUnits::VariantAndLineItemNaming
     include LineItemStockChanges
 
-    self.belongs_to_required_by_default = false
-
     searchable_attributes :price, :quantity, :order_id, :variant_id, :tax_category_id
     searchable_associations :order, :order_cycle, :variant, :product, :supplier, :tax_category
     searchable_scopes :with_tax, :without_tax
@@ -19,7 +17,7 @@ module Spree
     belongs_to :variant, -> { with_deleted }, class_name: "Spree::Variant"
     has_one :product, through: :variant
     has_one :supplier, through: :product
-    belongs_to :tax_category, class_name: "Spree::TaxCategory"
+    belongs_to :tax_category, class_name: "Spree::TaxCategory", optional: true
 
     has_many :adjustments, as: :adjustable, dependent: :destroy
 
@@ -28,7 +26,6 @@ module Spree
     before_validation :copy_tax_category
     before_validation :copy_dimensions
 
-    validates :variant, presence: true
     validates :quantity, numericality: {
       only_integer: true,
       greater_than: -1,

db/migrate/20240529081209_require_order_and_variant_on_line_item.rb

@@ -0,0 +1,6 @@
+class RequireOrderAndVariantOnLineItem < ActiveRecord::Migration[7.0]
+  def change
+    change_column_null :spree_line_items, :order_id, false
+    change_column_null :spree_line_items, :variant_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_17_121235) do
+ActiveRecord::Schema[7.0].define(version: 2024_05_29_081209) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_stat_statements"
   enable_extension "plpgsql"
@@ -541,8 +541,8 @@ ActiveRecord::Schema[7.0].define(version: 2024_05_17_121235) do
   end
 
   create_table "spree_line_items", id: :serial, force: :cascade do |t|
-    t.integer "order_id"
-    t.integer "variant_id"
+    t.integer "order_id", null: false
+    t.integer "variant_id", null: false
     t.integer "quantity", null: false
     t.decimal "price", precision: 10, scale: 2, null: false
     t.datetime "created_at", precision: nil, null: false