From 56cb3efd135aae239a225aa525b146913eb8d366 Mon Sep 17 00:00:00 2001
From: Thomas von Deyen <thomas@vondeyen.com>
Date: Wed, 10 Jul 2019 10:02:55 +0200
Subject: [PATCH] Make all belongs_to associations optional

Since Rails 5.1 `belongs_to` associations are required by default.
We used to disable this option globally. This hack was removed recently.
Since this has the potential to break stores with unconsistent data
we need to make all `belongs_to` optional for now.
---
 .../models/concerns/spree/user_address_book.rb |  2 +-
 core/app/models/spree/address.rb               |  4 ++--
 core/app/models/spree/adjustment.rb            | 10 +++++-----
 core/app/models/spree/asset.rb                 |  2 +-
 core/app/models/spree/calculator.rb            |  2 +-
 core/app/models/spree/carton.rb                |  6 +++---
 core/app/models/spree/classification.rb        |  4 ++--
 core/app/models/spree/credit_card.rb           |  4 ++--
 core/app/models/spree/customer_return.rb       |  2 +-
 core/app/models/spree/inventory_unit.rb        |  8 ++++----
 core/app/models/spree/line_item.rb             |  6 +++---
 core/app/models/spree/line_item_action.rb      |  4 ++--
 core/app/models/spree/log_entry.rb             |  2 +-
 core/app/models/spree/option_value.rb          |  2 +-
 core/app/models/spree/option_values_variant.rb |  4 ++--
 core/app/models/spree/order.rb                 | 14 +++++++-------
 core/app/models/spree/order_mutex.rb           |  2 +-
 core/app/models/spree/order_promotion.rb       |  6 +++---
 core/app/models/spree/payment.rb               |  6 +++---
 core/app/models/spree/payment_capture_event.rb |  2 +-
 core/app/models/spree/payment_source.rb        |  2 +-
 core/app/models/spree/price.rb                 |  4 ++--
 core/app/models/spree/product.rb               |  4 ++--
 core/app/models/spree/product_option_type.rb   |  4 ++--
 .../app/models/spree/product_promotion_rule.rb |  4 ++--
 core/app/models/spree/product_property.rb      |  4 ++--
 core/app/models/spree/promotion.rb             |  2 +-
 core/app/models/spree/promotion_action.rb      |  2 +-
 core/app/models/spree/promotion_code.rb        |  4 ++--
 core/app/models/spree/promotion_code_batch.rb  |  2 +-
 core/app/models/spree/promotion_rule.rb        |  2 +-
 core/app/models/spree/promotion_rule_role.rb   |  4 ++--
 core/app/models/spree/promotion_rule_store.rb  |  4 ++--
 core/app/models/spree/promotion_rule_taxon.rb  |  4 ++--
 core/app/models/spree/promotion_rule_user.rb   |  4 ++--
 core/app/models/spree/refund.rb                |  6 +++---
 core/app/models/spree/reimbursement.rb         |  4 ++--
 core/app/models/spree/reimbursement/credit.rb  |  4 ++--
 core/app/models/spree/return_authorization.rb  |  6 +++---
 core/app/models/spree/return_item.rb           | 18 +++++++++---------
 core/app/models/spree/role_user.rb             |  4 ++--
 core/app/models/spree/shipment.rb              |  4 ++--
 core/app/models/spree/shipping_method.rb       |  2 +-
 .../models/spree/shipping_method_category.rb   |  4 ++--
 .../spree/shipping_method_stock_location.rb    |  4 ++--
 core/app/models/spree/shipping_method_zone.rb  |  4 ++--
 core/app/models/spree/shipping_rate.rb         |  4 ++--
 core/app/models/spree/shipping_rate_tax.rb     |  4 ++--
 core/app/models/spree/state.rb                 |  2 +-
 core/app/models/spree/state_change.rb          |  4 ++--
 core/app/models/spree/stock_item.rb            |  4 ++--
 core/app/models/spree/stock_location.rb        |  4 ++--
 core/app/models/spree/stock_movement.rb        |  4 ++--
 core/app/models/spree/store_credit.rb          |  8 ++++----
 core/app/models/spree/store_credit_event.rb    |  6 +++---
 core/app/models/spree/store_payment_method.rb  |  4 ++--
 core/app/models/spree/store_shipping_method.rb |  4 ++--
 core/app/models/spree/tax_rate.rb              |  2 +-
 core/app/models/spree/tax_rate_tax_category.rb |  4 ++--
 core/app/models/spree/unit_cancel.rb           |  2 +-
 core/app/models/spree/user_address.rb          |  4 ++--
 core/app/models/spree/user_stock_location.rb   |  4 ++--
 core/app/models/spree/variant.rb               |  2 +-
 core/app/models/spree/variant_property_rule.rb |  2 +-
 .../spree/variant_property_rule_condition.rb   |  4 ++--
 .../spree/variant_property_rule_value.rb       |  4 ++--
 core/app/models/spree/wallet_payment_source.rb |  4 ++--
 core/app/models/spree/zone_member.rb           |  4 ++--
 68 files changed, 143 insertions(+), 143 deletions(-)

diff --git a/core/app/models/concerns/spree/user_address_book.rb b/core/app/models/concerns/spree/user_address_book.rb
index eb543036c35..466dbd826b9 100644
--- a/core/app/models/concerns/spree/user_address_book.rb
+++ b/core/app/models/concerns/spree/user_address_book.rb
@@ -25,7 +25,7 @@ def mark_default(user_address)
       has_many :addresses, through: :user_addresses
 
       # bill_address is only minimally used now, but we can't get rid of it without a major version release
-      belongs_to :bill_address, class_name: 'Spree::Address'
+      belongs_to :bill_address, class_name: 'Spree::Address', optional: true
 
       has_one :default_user_address, ->{ default }, class_name: 'Spree::UserAddress', foreign_key: 'user_id'
       has_one :default_address, through: :default_user_address, source: :address
diff --git a/core/app/models/spree/address.rb b/core/app/models/spree/address.rb
index aec76e284e2..6513997f068 100644
--- a/core/app/models/spree/address.rb
+++ b/core/app/models/spree/address.rb
@@ -8,8 +8,8 @@ module Spree
   class Address < Spree::Base
     extend ActiveModel::ForbiddenAttributesProtection
 
-    belongs_to :country, class_name: "Spree::Country"
-    belongs_to :state, class_name: "Spree::State"
+    belongs_to :country, class_name: "Spree::Country", optional: true
+    belongs_to :state, class_name: "Spree::State", optional: true
 
     validates :firstname, :address1, :city, :country_id, presence: true
     validates :zipcode, presence: true, if: :require_zipcode?
diff --git a/core/app/models/spree/adjustment.rb b/core/app/models/spree/adjustment.rb
index 8f16c80fc72..2425ed19b38 100644
--- a/core/app/models/spree/adjustment.rb
+++ b/core/app/models/spree/adjustment.rb
@@ -16,11 +16,11 @@ module Spree
   #    order's adjustment total. This allows an adjustment to be preserved if
   #    it becomes ineligible so it might be reinstated.
   class Adjustment < Spree::Base
-    belongs_to :adjustable, polymorphic: true, touch: true
-    belongs_to :source, polymorphic: true
-    belongs_to :order, class_name: 'Spree::Order', inverse_of: :all_adjustments
-    belongs_to :promotion_code, class_name: 'Spree::PromotionCode'
-    belongs_to :adjustment_reason, class_name: 'Spree::AdjustmentReason', inverse_of: :adjustments
+    belongs_to :adjustable, polymorphic: true, touch: true, optional: true
+    belongs_to :source, polymorphic: true, optional: true
+    belongs_to :order, class_name: 'Spree::Order', inverse_of: :all_adjustments, optional: true
+    belongs_to :promotion_code, class_name: 'Spree::PromotionCode', optional: true
+    belongs_to :adjustment_reason, class_name: 'Spree::AdjustmentReason', inverse_of: :adjustments, optional: true
 
     validates :adjustable, presence: true
     validates :order, presence: true
diff --git a/core/app/models/spree/asset.rb b/core/app/models/spree/asset.rb
index 27ea73ac218..aed2412478f 100644
--- a/core/app/models/spree/asset.rb
+++ b/core/app/models/spree/asset.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class Asset < Spree::Base
-    belongs_to :viewable, polymorphic: true, touch: true
+    belongs_to :viewable, polymorphic: true, touch: true, optional: true
     acts_as_list scope: [:viewable_id, :viewable_type]
   end
 end
diff --git a/core/app/models/spree/calculator.rb b/core/app/models/spree/calculator.rb
index 0bec110dcb1..2773570b1b7 100644
--- a/core/app/models/spree/calculator.rb
+++ b/core/app/models/spree/calculator.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class Calculator < Spree::Base
-    belongs_to :calculable, polymorphic: true
+    belongs_to :calculable, polymorphic: true, optional: true
 
     # This method calls a compute_<computable> method. must be overriden in concrete calculator.
     #
diff --git a/core/app/models/spree/carton.rb b/core/app/models/spree/carton.rb
index 444d7080dff..931b3b62dff 100644
--- a/core/app/models/spree/carton.rb
+++ b/core/app/models/spree/carton.rb
@@ -1,9 +1,9 @@
 # frozen_string_literal: true
 
 class Spree::Carton < Spree::Base
-  belongs_to :address, class_name: 'Spree::Address'
-  belongs_to :stock_location, class_name: 'Spree::StockLocation', inverse_of: :cartons
-  belongs_to :shipping_method, class_name: 'Spree::ShippingMethod', inverse_of: :cartons
+  belongs_to :address, class_name: 'Spree::Address', optional: true
+  belongs_to :stock_location, class_name: 'Spree::StockLocation', inverse_of: :cartons, optional: true
+  belongs_to :shipping_method, class_name: 'Spree::ShippingMethod', inverse_of: :cartons, optional: true
 
   has_many :inventory_units, class_name: "Spree::InventoryUnit", inverse_of: :carton, dependent: :nullify
   has_many :orders, -> { distinct }, through: :inventory_units
diff --git a/core/app/models/spree/classification.rb b/core/app/models/spree/classification.rb
index 8a4446c181d..4966625014a 100644
--- a/core/app/models/spree/classification.rb
+++ b/core/app/models/spree/classification.rb
@@ -4,8 +4,8 @@ module Spree
   class Classification < Spree::Base
     self.table_name = 'spree_products_taxons'
     acts_as_list scope: :taxon
-    belongs_to :product, class_name: "Spree::Product", inverse_of: :classifications, touch: true
-    belongs_to :taxon, class_name: "Spree::Taxon", inverse_of: :classifications, touch: true
+    belongs_to :product, class_name: "Spree::Product", inverse_of: :classifications, touch: true, optional: true
+    belongs_to :taxon, class_name: "Spree::Taxon", inverse_of: :classifications, touch: true, optional: true
 
     # For https://github.com/spree/spree/issues/3494
     validates_uniqueness_of :taxon_id, scope: :product_id, message: :already_linked
diff --git a/core/app/models/spree/credit_card.rb b/core/app/models/spree/credit_card.rb
index be71ae57dca..c3f6362b8ae 100644
--- a/core/app/models/spree/credit_card.rb
+++ b/core/app/models/spree/credit_card.rb
@@ -4,8 +4,8 @@ module Spree
   # The default `source` of a `Spree::Payment`.
   #
   class CreditCard < Spree::PaymentSource
-    belongs_to :user, class_name: Spree::UserClassHandle.new, foreign_key: 'user_id'
-    belongs_to :address
+    belongs_to :user, class_name: Spree::UserClassHandle.new, foreign_key: 'user_id', optional: true
+    belongs_to :address, optional: true
 
     before_save :set_last_digits
 
diff --git a/core/app/models/spree/customer_return.rb b/core/app/models/spree/customer_return.rb
index de9276b618a..6062b06008a 100644
--- a/core/app/models/spree/customer_return.rb
+++ b/core/app/models/spree/customer_return.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class CustomerReturn < Spree::Base
-    belongs_to :stock_location
+    belongs_to :stock_location, optional: true
 
     has_many :return_items, inverse_of: :customer_return
     has_many :return_authorizations, through: :return_items
diff --git a/core/app/models/spree/inventory_unit.rb b/core/app/models/spree/inventory_unit.rb
index 14e677b076a..34f51dcd3de 100644
--- a/core/app/models/spree/inventory_unit.rb
+++ b/core/app/models/spree/inventory_unit.rb
@@ -8,10 +8,10 @@ class InventoryUnit < Spree::Base
     POST_SHIPMENT_STATES = %w(returned)
     CANCELABLE_STATES = ['on_hand', 'backordered', 'shipped']
 
-    belongs_to :variant, -> { with_deleted }, class_name: "Spree::Variant", inverse_of: :inventory_units
-    belongs_to :shipment, class_name: "Spree::Shipment", touch: true, inverse_of: :inventory_units
-    belongs_to :carton, class_name: "Spree::Carton", inverse_of: :inventory_units
-    belongs_to :line_item, class_name: "Spree::LineItem", inverse_of: :inventory_units
+    belongs_to :variant, -> { with_deleted }, class_name: "Spree::Variant", inverse_of: :inventory_units, optional: true
+    belongs_to :shipment, class_name: "Spree::Shipment", touch: true, inverse_of: :inventory_units, optional: true
+    belongs_to :carton, class_name: "Spree::Carton", inverse_of: :inventory_units, optional: true
+    belongs_to :line_item, class_name: "Spree::LineItem", inverse_of: :inventory_units, optional: true
 
     has_many :return_items, inverse_of: :inventory_unit, dependent: :destroy
     has_one :original_return_item, class_name: "Spree::ReturnItem", foreign_key: :exchange_inventory_unit_id, dependent: :destroy
diff --git a/core/app/models/spree/line_item.rb b/core/app/models/spree/line_item.rb
index 5181e9a5464..79e24863319 100644
--- a/core/app/models/spree/line_item.rb
+++ b/core/app/models/spree/line_item.rb
@@ -12,9 +12,9 @@ module Spree
   class LineItem < Spree::Base
     class CurrencyMismatch < StandardError; end
 
-    belongs_to :order, class_name: "Spree::Order", inverse_of: :line_items, touch: true
-    belongs_to :variant, -> { with_deleted }, class_name: "Spree::Variant", inverse_of: :line_items
-    belongs_to :tax_category, class_name: "Spree::TaxCategory"
+    belongs_to :order, class_name: "Spree::Order", inverse_of: :line_items, touch: true, optional: true
+    belongs_to :variant, -> { with_deleted }, class_name: "Spree::Variant", inverse_of: :line_items, optional: true
+    belongs_to :tax_category, class_name: "Spree::TaxCategory", optional: true
 
     has_one :product, through: :variant
 
diff --git a/core/app/models/spree/line_item_action.rb b/core/app/models/spree/line_item_action.rb
index 4d84bb0a13a..aa280298cf0 100644
--- a/core/app/models/spree/line_item_action.rb
+++ b/core/app/models/spree/line_item_action.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class LineItemAction < Spree::Base
-    belongs_to :line_item
-    belongs_to :action, class_name: "Spree::PromotionAction"
+    belongs_to :line_item, optional: true
+    belongs_to :action, class_name: "Spree::PromotionAction", optional: true
   end
 end
diff --git a/core/app/models/spree/log_entry.rb b/core/app/models/spree/log_entry.rb
index bd9ce217c8a..2e3bd32a456 100644
--- a/core/app/models/spree/log_entry.rb
+++ b/core/app/models/spree/log_entry.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class LogEntry < Spree::Base
-    belongs_to :source, polymorphic: true
+    belongs_to :source, polymorphic: true, optional: true
 
     def parsed_details
       @details ||= YAML.load(details)
diff --git a/core/app/models/spree/option_value.rb b/core/app/models/spree/option_value.rb
index 99e8577dc22..a0b79252b9a 100644
--- a/core/app/models/spree/option_value.rb
+++ b/core/app/models/spree/option_value.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class OptionValue < Spree::Base
-    belongs_to :option_type, class_name: 'Spree::OptionType', inverse_of: :option_values
+    belongs_to :option_type, class_name: 'Spree::OptionType', inverse_of: :option_values, optional: true
     acts_as_list scope: :option_type
 
     has_many :option_values_variants, dependent: :destroy
diff --git a/core/app/models/spree/option_values_variant.rb b/core/app/models/spree/option_values_variant.rb
index 18d4766ec9d..58742f54b46 100644
--- a/core/app/models/spree/option_values_variant.rb
+++ b/core/app/models/spree/option_values_variant.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class OptionValuesVariant < Spree::Base
-    belongs_to :variant
-    belongs_to :option_value
+    belongs_to :variant, optional: true
+    belongs_to :option_value, optional: true
   end
 end
diff --git a/core/app/models/spree/order.rb b/core/app/models/spree/order.rb
index bde803c1d48..719e348581f 100644
--- a/core/app/models/spree/order.rb
+++ b/core/app/models/spree/order.rb
@@ -55,15 +55,15 @@ class CannotRebuildShipments < StandardError; end
     deprecate :temporary_credit_card= => :temporary_payment_source=, deprecator: Spree::Deprecation
 
     # Customer info
-    belongs_to :user, class_name: Spree::UserClassHandle.new
-    belongs_to :bill_address, foreign_key: :bill_address_id, class_name: 'Spree::Address'
+    belongs_to :user, class_name: Spree::UserClassHandle.new, optional: true
+    belongs_to :bill_address, foreign_key: :bill_address_id, class_name: 'Spree::Address', optional: true
     alias_attribute :billing_address, :bill_address
 
-    belongs_to :ship_address, foreign_key: :ship_address_id, class_name: 'Spree::Address'
+    belongs_to :ship_address, foreign_key: :ship_address_id, class_name: 'Spree::Address', optional: true
     alias_attribute :shipping_address, :ship_address
     alias_attribute :ship_total, :shipment_total
 
-    belongs_to :store, class_name: 'Spree::Store'
+    belongs_to :store, class_name: 'Spree::Store', optional: true
 
     # Items
     has_many :line_items, -> { order(:created_at, :id) }, dependent: :destroy, inverse_of: :order
@@ -101,9 +101,9 @@ def states
 
     # Logging
     has_many :state_changes, as: :stateful
-    belongs_to :created_by, class_name: Spree::UserClassHandle.new
-    belongs_to :approver, class_name: Spree::UserClassHandle.new
-    belongs_to :canceler, class_name: Spree::UserClassHandle.new
+    belongs_to :created_by, class_name: Spree::UserClassHandle.new, optional: true
+    belongs_to :approver, class_name: Spree::UserClassHandle.new, optional: true
+    belongs_to :canceler, class_name: Spree::UserClassHandle.new, optional: true
 
     accepts_nested_attributes_for :line_items
     accepts_nested_attributes_for :bill_address
diff --git a/core/app/models/spree/order_mutex.rb b/core/app/models/spree/order_mutex.rb
index 503ceb7092f..4fca9fd193a 100644
--- a/core/app/models/spree/order_mutex.rb
+++ b/core/app/models/spree/order_mutex.rb
@@ -4,7 +4,7 @@ module Spree
   class OrderMutex < Spree::Base
     class LockFailed < StandardError; end
 
-    belongs_to :order, class_name: "Spree::Order"
+    belongs_to :order, class_name: "Spree::Order", optional: true
 
     scope :expired, -> { where(arel_table[:created_at].lteq(Spree::Config[:order_mutex_max_age].seconds.ago)) }
 
diff --git a/core/app/models/spree/order_promotion.rb b/core/app/models/spree/order_promotion.rb
index 07450fa9598..b2a5464c2fc 100644
--- a/core/app/models/spree/order_promotion.rb
+++ b/core/app/models/spree/order_promotion.rb
@@ -8,9 +8,9 @@ module Spree
   class OrderPromotion < Spree::Base
     self.table_name = 'spree_orders_promotions'
 
-    belongs_to :order, class_name: 'Spree::Order'
-    belongs_to :promotion, class_name: 'Spree::Promotion'
-    belongs_to :promotion_code, class_name: 'Spree::PromotionCode'
+    belongs_to :order, class_name: 'Spree::Order', optional: true
+    belongs_to :promotion, class_name: 'Spree::Promotion', optional: true
+    belongs_to :promotion_code, class_name: 'Spree::PromotionCode', optional: true
 
     validates :order, presence: true
     validates :promotion, presence: true
diff --git a/core/app/models/spree/payment.rb b/core/app/models/spree/payment.rb
index d9889db7517..701c83cdf17 100644
--- a/core/app/models/spree/payment.rb
+++ b/core/app/models/spree/payment.rb
@@ -15,9 +15,9 @@ class Payment < Spree::Base
     NON_RISKY_AVS_CODES = ['B', 'D', 'H', 'J', 'M', 'Q', 'T', 'V', 'X', 'Y'].freeze
     RISKY_AVS_CODES     = ['A', 'C', 'E', 'F', 'G', 'I', 'K', 'L', 'N', 'O', 'P', 'R', 'S', 'U', 'W', 'Z'].freeze
 
-    belongs_to :order, class_name: 'Spree::Order', touch: true, inverse_of: :payments
-    belongs_to :source, polymorphic: true
-    belongs_to :payment_method, -> { with_deleted }, class_name: 'Spree::PaymentMethod', inverse_of: :payments
+    belongs_to :order, class_name: 'Spree::Order', touch: true, inverse_of: :payments, optional: true
+    belongs_to :source, polymorphic: true, optional: true
+    belongs_to :payment_method, -> { with_deleted }, class_name: 'Spree::PaymentMethod', inverse_of: :payments, optional: true
 
     has_many :offsets, -> { offset_payment }, class_name: "Spree::Payment", foreign_key: :source_id
     has_many :log_entries, as: :source
diff --git a/core/app/models/spree/payment_capture_event.rb b/core/app/models/spree/payment_capture_event.rb
index c137c345420..b6fcb143edc 100644
--- a/core/app/models/spree/payment_capture_event.rb
+++ b/core/app/models/spree/payment_capture_event.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class PaymentCaptureEvent < Spree::Base
-    belongs_to :payment, class_name: 'Spree::Payment'
+    belongs_to :payment, class_name: 'Spree::Payment', optional: true
 
     def display_amount
       Spree::Money.new(amount, { currency: payment.currency })
diff --git a/core/app/models/spree/payment_source.rb b/core/app/models/spree/payment_source.rb
index f7ab8590d3a..91b17cc77c6 100644
--- a/core/app/models/spree/payment_source.rb
+++ b/core/app/models/spree/payment_source.rb
@@ -4,7 +4,7 @@ module Spree
   class PaymentSource < Spree::Base
     self.abstract_class = true
 
-    belongs_to :payment_method
+    belongs_to :payment_method, optional: true
 
     has_many :payments, as: :source
     has_many :wallet_payment_sources, class_name: 'Spree::WalletPaymentSource', as: :payment_source, inverse_of: :payment_source
diff --git a/core/app/models/spree/price.rb b/core/app/models/spree/price.rb
index 7b60356dcc4..198b6ac7943 100644
--- a/core/app/models/spree/price.rb
+++ b/core/app/models/spree/price.rb
@@ -12,8 +12,8 @@ class Price < Spree::Base
 
     MAXIMUM_AMOUNT = BigDecimal('99_999_999.99')
 
-    belongs_to :variant, -> { with_deleted }, class_name: 'Spree::Variant', touch: true
-    belongs_to :country, class_name: "Spree::Country", foreign_key: "country_iso", primary_key: "iso"
+    belongs_to :variant, -> { with_deleted }, class_name: 'Spree::Variant', touch: true, optional: true
+    belongs_to :country, class_name: "Spree::Country", foreign_key: "country_iso", primary_key: "iso", optional: true
 
     delegate :product, to: :variant
     delegate :tax_rates, to: :variant
diff --git a/core/app/models/spree/product.rb b/core/app/models/spree/product.rb
index 907c63436cf..04d0ddb34fa 100644
--- a/core/app/models/spree/product.rb
+++ b/core/app/models/spree/product.rb
@@ -44,8 +44,8 @@ class Product < Spree::Base
     has_many :product_promotion_rules, dependent: :destroy
     has_many :promotion_rules, through: :product_promotion_rules
 
-    belongs_to :tax_category, class_name: 'Spree::TaxCategory'
-    belongs_to :shipping_category, class_name: 'Spree::ShippingCategory', inverse_of: :products
+    belongs_to :tax_category, class_name: 'Spree::TaxCategory', optional: true
+    belongs_to :shipping_category, class_name: 'Spree::ShippingCategory', inverse_of: :products, optional: true
 
     has_one :master,
       -> { where(is_master: true).with_deleted },
diff --git a/core/app/models/spree/product_option_type.rb b/core/app/models/spree/product_option_type.rb
index 4c0f398ea7a..cf1f7704dbc 100644
--- a/core/app/models/spree/product_option_type.rb
+++ b/core/app/models/spree/product_option_type.rb
@@ -2,8 +2,8 @@
 
 module Spree
   class ProductOptionType < Spree::Base
-    belongs_to :product, class_name: 'Spree::Product', inverse_of: :product_option_types, touch: true
-    belongs_to :option_type, class_name: 'Spree::OptionType', inverse_of: :product_option_types
+    belongs_to :product, class_name: 'Spree::Product', inverse_of: :product_option_types, touch: true, optional: true
+    belongs_to :option_type, class_name: 'Spree::OptionType', inverse_of: :product_option_types, optional: true
     acts_as_list scope: :product
   end
 end
diff --git a/core/app/models/spree/product_promotion_rule.rb b/core/app/models/spree/product_promotion_rule.rb
index 98a29893e30..c12df3f4be9 100644
--- a/core/app/models/spree/product_promotion_rule.rb
+++ b/core/app/models/spree/product_promotion_rule.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class ProductPromotionRule < Spree::Base
-    belongs_to :product
-    belongs_to :promotion_rule
+    belongs_to :product, optional: true
+    belongs_to :promotion_rule, optional: true
   end
 end
diff --git a/core/app/models/spree/product_property.rb b/core/app/models/spree/product_property.rb
index 6e0c383ab12..a5f91b719e6 100644
--- a/core/app/models/spree/product_property.rb
+++ b/core/app/models/spree/product_property.rb
@@ -6,8 +6,8 @@ class ProductProperty < Spree::Base
 
     acts_as_list scope: :product
 
-    belongs_to :product, touch: true, class_name: 'Spree::Product', inverse_of: :product_properties
-    belongs_to :property, class_name: 'Spree::Property', inverse_of: :product_properties
+    belongs_to :product, touch: true, class_name: 'Spree::Product', inverse_of: :product_properties, optional: true
+    belongs_to :property, class_name: 'Spree::Property', inverse_of: :product_properties, optional: true
 
     self.whitelisted_ransackable_attributes = ['value']
   end
diff --git a/core/app/models/spree/promotion.rb b/core/app/models/spree/promotion.rb
index 47beaf010d0..bccc75b75c8 100644
--- a/core/app/models/spree/promotion.rb
+++ b/core/app/models/spree/promotion.rb
@@ -7,7 +7,7 @@ class Promotion < Spree::Base
 
     attr_reader :eligibility_errors
 
-    belongs_to :promotion_category
+    belongs_to :promotion_category, optional: true
 
     has_many :promotion_rules, autosave: true, dependent: :destroy, inverse_of: :promotion
     alias_method :rules, :promotion_rules
diff --git a/core/app/models/spree/promotion_action.rb b/core/app/models/spree/promotion_action.rb
index 25519060baa..e40262f678c 100644
--- a/core/app/models/spree/promotion_action.rb
+++ b/core/app/models/spree/promotion_action.rb
@@ -14,7 +14,7 @@ class PromotionAction < Spree::Base
     include Discard::Model
     self.discard_column = :deleted_at
 
-    belongs_to :promotion, class_name: 'Spree::Promotion', inverse_of: :promotion_actions
+    belongs_to :promotion, class_name: 'Spree::Promotion', inverse_of: :promotion_actions, optional: true
 
     scope :of_type, ->(t) { where(type: Array.wrap(t).map(&:to_s)) }
     scope :shipping, -> { of_type(Spree::Config.environment.promotions.shipping_actions.to_a) }
diff --git a/core/app/models/spree/promotion_code.rb b/core/app/models/spree/promotion_code.rb
index 8fc72ee7fe4..215c71d8f8c 100644
--- a/core/app/models/spree/promotion_code.rb
+++ b/core/app/models/spree/promotion_code.rb
@@ -1,8 +1,8 @@
 # frozen_string_literal: true
 
 class Spree::PromotionCode < Spree::Base
-  belongs_to :promotion, inverse_of: :codes
-  belongs_to :promotion_code_batch, class_name: "Spree::PromotionCodeBatch"
+  belongs_to :promotion, inverse_of: :codes, optional: true
+  belongs_to :promotion_code_batch, class_name: "Spree::PromotionCodeBatch", optional: true
   has_many :adjustments
 
   validates :value, presence: true, uniqueness: { allow_blank: true }
diff --git a/core/app/models/spree/promotion_code_batch.rb b/core/app/models/spree/promotion_code_batch.rb
index 755a9ba0436..699885164cc 100644
--- a/core/app/models/spree/promotion_code_batch.rb
+++ b/core/app/models/spree/promotion_code_batch.rb
@@ -5,7 +5,7 @@ class PromotionCodeBatch < ActiveRecord::Base
     class CantProcessStartedBatch < StandardError
     end
 
-    belongs_to :promotion, class_name: "Spree::Promotion"
+    belongs_to :promotion, class_name: "Spree::Promotion", optional: true
     has_many :promotion_codes, class_name: "Spree::PromotionCode", dependent: :destroy
 
     validates :number_of_codes, numericality: { greater_than: 0 }
diff --git a/core/app/models/spree/promotion_rule.rb b/core/app/models/spree/promotion_rule.rb
index bbc2b67f1c3..22791d9f471 100644
--- a/core/app/models/spree/promotion_rule.rb
+++ b/core/app/models/spree/promotion_rule.rb
@@ -3,7 +3,7 @@
 module Spree
   # Base class for all promotion rules
   class PromotionRule < Spree::Base
-    belongs_to :promotion, class_name: 'Spree::Promotion', inverse_of: :promotion_rules
+    belongs_to :promotion, class_name: 'Spree::Promotion', inverse_of: :promotion_rules, optional: true
 
     scope :of_type, ->(t) { where(type: t) }
 
diff --git a/core/app/models/spree/promotion_rule_role.rb b/core/app/models/spree/promotion_rule_role.rb
index 2d9243438c8..f6dc3b7a022 100644
--- a/core/app/models/spree/promotion_rule_role.rb
+++ b/core/app/models/spree/promotion_rule_role.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class PromotionRuleRole < ActiveRecord::Base
-    belongs_to :promotion_rule, class_name: 'Spree::PromotionRule'
-    belongs_to :role, class_name: 'Spree::Role'
+    belongs_to :promotion_rule, class_name: 'Spree::PromotionRule', optional: true
+    belongs_to :role, class_name: 'Spree::Role', optional: true
   end
 end
diff --git a/core/app/models/spree/promotion_rule_store.rb b/core/app/models/spree/promotion_rule_store.rb
index db013de164b..d0456cd728c 100644
--- a/core/app/models/spree/promotion_rule_store.rb
+++ b/core/app/models/spree/promotion_rule_store.rb
@@ -4,7 +4,7 @@ module Spree
   class PromotionRuleStore < Spree::Base
     self.table_name = "spree_promotion_rules_stores"
 
-    belongs_to :promotion_rule, class_name: "Spree::PromotionRule"
-    belongs_to :store, class_name: "Spree::Store"
+    belongs_to :promotion_rule, class_name: "Spree::PromotionRule", optional: true
+    belongs_to :store, class_name: "Spree::Store", optional: true
   end
 end
diff --git a/core/app/models/spree/promotion_rule_taxon.rb b/core/app/models/spree/promotion_rule_taxon.rb
index ccf6e434556..7df3f008870 100644
--- a/core/app/models/spree/promotion_rule_taxon.rb
+++ b/core/app/models/spree/promotion_rule_taxon.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class PromotionRuleTaxon < Spree::Base
-    belongs_to :promotion_rule
-    belongs_to :taxon
+    belongs_to :promotion_rule, optional: true
+    belongs_to :taxon, optional: true
   end
 end
diff --git a/core/app/models/spree/promotion_rule_user.rb b/core/app/models/spree/promotion_rule_user.rb
index 432afb826ab..8f269533ccb 100644
--- a/core/app/models/spree/promotion_rule_user.rb
+++ b/core/app/models/spree/promotion_rule_user.rb
@@ -4,7 +4,7 @@ module Spree
   class PromotionRuleUser < Spree::Base
     self.table_name = 'spree_promotion_rules_users'
 
-    belongs_to :promotion_rule, class_name: 'Spree::PromotionRule'
-    belongs_to :user, class_name: Spree::UserClassHandle.new
+    belongs_to :promotion_rule, class_name: 'Spree::PromotionRule', optional: true
+    belongs_to :user, class_name: Spree::UserClassHandle.new, optional: true
   end
 end
diff --git a/core/app/models/spree/refund.rb b/core/app/models/spree/refund.rb
index e26ecc1ad8d..b8caf0a8879 100644
--- a/core/app/models/spree/refund.rb
+++ b/core/app/models/spree/refund.rb
@@ -2,9 +2,9 @@
 
 module Spree
   class Refund < Spree::Base
-    belongs_to :payment, inverse_of: :refunds
-    belongs_to :reason, class_name: 'Spree::RefundReason', foreign_key: :refund_reason_id
-    belongs_to :reimbursement, inverse_of: :refunds
+    belongs_to :payment, inverse_of: :refunds, optional: true
+    belongs_to :reason, class_name: 'Spree::RefundReason', foreign_key: :refund_reason_id, optional: true
+    belongs_to :reimbursement, inverse_of: :refunds, optional: true
 
     has_many :log_entries, as: :source
 
diff --git a/core/app/models/spree/reimbursement.rb b/core/app/models/spree/reimbursement.rb
index e4309166174..c1739ccabc7 100644
--- a/core/app/models/spree/reimbursement.rb
+++ b/core/app/models/spree/reimbursement.rb
@@ -4,8 +4,8 @@ module Spree
   class Reimbursement < Spree::Base
     class IncompleteReimbursementError < StandardError; end
 
-    belongs_to :order, inverse_of: :reimbursements
-    belongs_to :customer_return, inverse_of: :reimbursements, touch: true
+    belongs_to :order, inverse_of: :reimbursements, optional: true
+    belongs_to :customer_return, inverse_of: :reimbursements, touch: true, optional: true
 
     has_many :refunds, inverse_of: :reimbursement
     has_many :credits, inverse_of: :reimbursement, class_name: 'Spree::Reimbursement::Credit'
diff --git a/core/app/models/spree/reimbursement/credit.rb b/core/app/models/spree/reimbursement/credit.rb
index dac5a16235d..2119656b81e 100644
--- a/core/app/models/spree/reimbursement/credit.rb
+++ b/core/app/models/spree/reimbursement/credit.rb
@@ -6,8 +6,8 @@ class Credit < Spree::Base
       class_attribute :default_creditable_class
       self.default_creditable_class = Spree::StoreCredit
 
-      belongs_to :reimbursement, inverse_of: :credits
-      belongs_to :creditable, polymorphic: true
+      belongs_to :reimbursement, inverse_of: :credits, optional: true
+      belongs_to :creditable, polymorphic: true, optional: true
 
       validates :creditable, presence: true
 
diff --git a/core/app/models/spree/return_authorization.rb b/core/app/models/spree/return_authorization.rb
index 8aba85b7ee2..35a6d80b817 100644
--- a/core/app/models/spree/return_authorization.rb
+++ b/core/app/models/spree/return_authorization.rb
@@ -4,14 +4,14 @@ module Spree
   # Models the return of Inventory Units to a Stock Location for an Order.
   #
   class ReturnAuthorization < Spree::Base
-    belongs_to :order, class_name: 'Spree::Order', inverse_of: :return_authorizations
+    belongs_to :order, class_name: 'Spree::Order', inverse_of: :return_authorizations, optional: true
 
     has_many :return_items, inverse_of: :return_authorization, dependent: :destroy
     has_many :inventory_units, through: :return_items, dependent: :nullify
     has_many :customer_returns, through: :return_items
 
-    belongs_to :stock_location
-    belongs_to :reason, class_name: 'Spree::ReturnReason', foreign_key: :return_reason_id
+    belongs_to :stock_location, optional: true
+    belongs_to :reason, class_name: 'Spree::ReturnReason', foreign_key: :return_reason_id, optional: true
 
     before_create :generate_number
 
diff --git a/core/app/models/spree/return_item.rb b/core/app/models/spree/return_item.rb
index c67bdc33bcc..c07a1f59ab3 100644
--- a/core/app/models/spree/return_item.rb
+++ b/core/app/models/spree/return_item.rb
@@ -29,15 +29,15 @@ class ReturnItem < Spree::Base
     class_attribute :refund_amount_calculator
     self.refund_amount_calculator = Calculator::Returns::DefaultRefundAmount
 
-    belongs_to :return_authorization, inverse_of: :return_items
-    belongs_to :inventory_unit, inverse_of: :return_items
-    belongs_to :exchange_variant, class_name: 'Spree::Variant'
-    belongs_to :exchange_inventory_unit, class_name: 'Spree::InventoryUnit', inverse_of: :original_return_item
-    belongs_to :customer_return, inverse_of: :return_items
-    belongs_to :reimbursement, inverse_of: :return_items
-    belongs_to :preferred_reimbursement_type, class_name: 'Spree::ReimbursementType'
-    belongs_to :override_reimbursement_type, class_name: 'Spree::ReimbursementType'
-    belongs_to :return_reason, class_name: 'Spree::ReturnReason', foreign_key: :return_reason_id
+    belongs_to :return_authorization, inverse_of: :return_items, optional: true
+    belongs_to :inventory_unit, inverse_of: :return_items, optional: true
+    belongs_to :exchange_variant, class_name: 'Spree::Variant', optional: true
+    belongs_to :exchange_inventory_unit, class_name: 'Spree::InventoryUnit', inverse_of: :original_return_item, optional: true
+    belongs_to :customer_return, inverse_of: :return_items, optional: true
+    belongs_to :reimbursement, inverse_of: :return_items, optional: true
+    belongs_to :preferred_reimbursement_type, class_name: 'Spree::ReimbursementType', optional: true
+    belongs_to :override_reimbursement_type, class_name: 'Spree::ReimbursementType', optional: true
+    belongs_to :return_reason, class_name: 'Spree::ReturnReason', foreign_key: :return_reason_id, optional: true
 
     validate :eligible_exchange_variant
     validate :belongs_to_same_customer_order
diff --git a/core/app/models/spree/role_user.rb b/core/app/models/spree/role_user.rb
index 449049bd30a..c4aa044531c 100644
--- a/core/app/models/spree/role_user.rb
+++ b/core/app/models/spree/role_user.rb
@@ -3,8 +3,8 @@
 module Spree
   class RoleUser < Spree::Base
     self.table_name = "spree_roles_users"
-    belongs_to :role, class_name: "Spree::Role"
-    belongs_to :user, class_name: Spree::UserClassHandle.new
+    belongs_to :role, class_name: "Spree::Role", optional: true
+    belongs_to :user, class_name: Spree::UserClassHandle.new, optional: true
 
     after_create :auto_generate_spree_api_key
 
diff --git a/core/app/models/spree/shipment.rb b/core/app/models/spree/shipment.rb
index 3c6535fe1a0..1ddbffe9f23 100644
--- a/core/app/models/spree/shipment.rb
+++ b/core/app/models/spree/shipment.rb
@@ -4,8 +4,8 @@ module Spree
   # An order's planned shipments including tracking and cost.
   #
   class Shipment < Spree::Base
-    belongs_to :order, class_name: 'Spree::Order', touch: true, inverse_of: :shipments
-    belongs_to :stock_location, class_name: 'Spree::StockLocation'
+    belongs_to :order, class_name: 'Spree::Order', touch: true, inverse_of: :shipments, optional: true
+    belongs_to :stock_location, class_name: 'Spree::StockLocation', optional: true
 
     has_many :adjustments, as: :adjustable, inverse_of: :adjustable, dependent: :delete_all
     has_many :inventory_units, dependent: :destroy, inverse_of: :shipment
diff --git a/core/app/models/spree/shipping_method.rb b/core/app/models/spree/shipping_method.rb
index 053528ade7b..008fb355811 100644
--- a/core/app/models/spree/shipping_method.rb
+++ b/core/app/models/spree/shipping_method.rb
@@ -28,7 +28,7 @@ class ShippingMethod < Spree::Base
     has_many :shipping_method_zones, dependent: :destroy
     has_many :zones, through: :shipping_method_zones
 
-    belongs_to :tax_category, -> { with_deleted }, class_name: 'Spree::TaxCategory'
+    belongs_to :tax_category, -> { with_deleted }, class_name: 'Spree::TaxCategory', optional: true
     has_many :shipping_method_stock_locations, dependent: :destroy, class_name: "Spree::ShippingMethodStockLocation"
     has_many :stock_locations, through: :shipping_method_stock_locations
 
diff --git a/core/app/models/spree/shipping_method_category.rb b/core/app/models/spree/shipping_method_category.rb
index 0d67a34506f..0a4072243a7 100644
--- a/core/app/models/spree/shipping_method_category.rb
+++ b/core/app/models/spree/shipping_method_category.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class ShippingMethodCategory < Spree::Base
-    belongs_to :shipping_method, class_name: 'Spree::ShippingMethod'
-    belongs_to :shipping_category, class_name: 'Spree::ShippingCategory', inverse_of: :shipping_method_categories
+    belongs_to :shipping_method, class_name: 'Spree::ShippingMethod', optional: true
+    belongs_to :shipping_category, class_name: 'Spree::ShippingCategory', inverse_of: :shipping_method_categories, optional: true
   end
 end
diff --git a/core/app/models/spree/shipping_method_stock_location.rb b/core/app/models/spree/shipping_method_stock_location.rb
index cadd852891d..792a584d8d5 100644
--- a/core/app/models/spree/shipping_method_stock_location.rb
+++ b/core/app/models/spree/shipping_method_stock_location.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
 class Spree::ShippingMethodStockLocation < Spree::Base
-  belongs_to :shipping_method
-  belongs_to :stock_location
+  belongs_to :shipping_method, optional: true
+  belongs_to :stock_location, optional: true
 end
diff --git a/core/app/models/spree/shipping_method_zone.rb b/core/app/models/spree/shipping_method_zone.rb
index 8262a60d3d9..c7526d0a298 100644
--- a/core/app/models/spree/shipping_method_zone.rb
+++ b/core/app/models/spree/shipping_method_zone.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class ShippingMethodZone < Spree::Base
-    belongs_to :zone
-    belongs_to :shipping_method
+    belongs_to :zone, optional: true
+    belongs_to :shipping_method, optional: true
   end
 end
diff --git a/core/app/models/spree/shipping_rate.rb b/core/app/models/spree/shipping_rate.rb
index c3d28f3afd7..2e7fe8c44d0 100644
--- a/core/app/models/spree/shipping_rate.rb
+++ b/core/app/models/spree/shipping_rate.rb
@@ -5,8 +5,8 @@ module Spree
   # method has been selected to deliver the shipment.
   #
   class ShippingRate < Spree::Base
-    belongs_to :shipment, class_name: 'Spree::Shipment', touch: true
-    belongs_to :shipping_method, -> { with_deleted }, class_name: 'Spree::ShippingMethod', inverse_of: :shipping_rates
+    belongs_to :shipment, class_name: 'Spree::Shipment', touch: true, optional: true
+    belongs_to :shipping_method, -> { with_deleted }, class_name: 'Spree::ShippingMethod', inverse_of: :shipping_rates, optional: true
 
     has_many :taxes,
              class_name: "Spree::ShippingRateTax",
diff --git a/core/app/models/spree/shipping_rate_tax.rb b/core/app/models/spree/shipping_rate_tax.rb
index 43b9d0dad09..c3528e4080c 100644
--- a/core/app/models/spree/shipping_rate_tax.rb
+++ b/core/app/models/spree/shipping_rate_tax.rb
@@ -7,8 +7,8 @@ module Spree
   # @since 1.3.0
   # @see Spree::Tax::ShippingRateTaxer
   class ShippingRateTax < ActiveRecord::Base
-    belongs_to :shipping_rate, class_name: "Spree::ShippingRate"
-    belongs_to :tax_rate, class_name: "Spree::TaxRate"
+    belongs_to :shipping_rate, class_name: "Spree::ShippingRate", optional: true
+    belongs_to :tax_rate, class_name: "Spree::TaxRate", optional: true
 
     extend DisplayMoney
     money_methods :absolute_amount
diff --git a/core/app/models/spree/state.rb b/core/app/models/spree/state.rb
index 7036cb63a71..503b0ea2d6a 100644
--- a/core/app/models/spree/state.rb
+++ b/core/app/models/spree/state.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class State < Spree::Base
-    belongs_to :country, class_name: 'Spree::Country'
+    belongs_to :country, class_name: 'Spree::Country', optional: true
     has_many :addresses, dependent: :nullify
 
     validates :country, :name, presence: true
diff --git a/core/app/models/spree/state_change.rb b/core/app/models/spree/state_change.rb
index d302287cba1..2e642c6d900 100644
--- a/core/app/models/spree/state_change.rb
+++ b/core/app/models/spree/state_change.rb
@@ -2,8 +2,8 @@
 
 module Spree
   class StateChange < Spree::Base
-    belongs_to :user
-    belongs_to :stateful, polymorphic: true
+    belongs_to :user, optional: true
+    belongs_to :stateful, polymorphic: true, optional: true
     before_create :assign_user
 
     def <=>(other)
diff --git a/core/app/models/spree/stock_item.rb b/core/app/models/spree/stock_item.rb
index 0b4d2b6d27e..3836b1097fe 100644
--- a/core/app/models/spree/stock_item.rb
+++ b/core/app/models/spree/stock_item.rb
@@ -10,8 +10,8 @@ class StockItem < Spree::Base
     include Discard::Model
     self.discard_column = :deleted_at
 
-    belongs_to :stock_location, class_name: 'Spree::StockLocation', inverse_of: :stock_items
-    belongs_to :variant, -> { with_deleted }, class_name: 'Spree::Variant', inverse_of: :stock_items
+    belongs_to :stock_location, class_name: 'Spree::StockLocation', inverse_of: :stock_items, optional: true
+    belongs_to :variant, -> { with_deleted }, class_name: 'Spree::Variant', inverse_of: :stock_items, optional: true
     has_many :stock_movements, inverse_of: :stock_item
 
     validates :stock_location, :variant, presence: true
diff --git a/core/app/models/spree/stock_location.rb b/core/app/models/spree/stock_location.rb
index faa53f5d80f..eca5ab1d85c 100644
--- a/core/app/models/spree/stock_location.rb
+++ b/core/app/models/spree/stock_location.rb
@@ -16,8 +16,8 @@ class InvalidMovementError < StandardError; end
     has_many :user_stock_locations, dependent: :delete_all
     has_many :users, through: :user_stock_locations
 
-    belongs_to :state, class_name: 'Spree::State'
-    belongs_to :country, class_name: 'Spree::Country'
+    belongs_to :state, class_name: 'Spree::State', optional: true
+    belongs_to :country, class_name: 'Spree::Country', optional: true
 
     has_many :shipping_method_stock_locations, dependent: :destroy
     has_many :shipping_methods, through: :shipping_method_stock_locations
diff --git a/core/app/models/spree/stock_movement.rb b/core/app/models/spree/stock_movement.rb
index 4ab1c45cc98..c4c11cf929a 100644
--- a/core/app/models/spree/stock_movement.rb
+++ b/core/app/models/spree/stock_movement.rb
@@ -2,8 +2,8 @@
 
 module Spree
   class StockMovement < Spree::Base
-    belongs_to :stock_item, class_name: 'Spree::StockItem', inverse_of: :stock_movements
-    belongs_to :originator, polymorphic: true
+    belongs_to :stock_item, class_name: 'Spree::StockItem', inverse_of: :stock_movements, optional: true
+    belongs_to :originator, polymorphic: true, optional: true
 
     after_create :update_stock_item_quantity
 
diff --git a/core/app/models/spree/store_credit.rb b/core/app/models/spree/store_credit.rb
index 970dacdd44b..9d33ec38b02 100644
--- a/core/app/models/spree/store_credit.rb
+++ b/core/app/models/spree/store_credit.rb
@@ -18,10 +18,10 @@ class Spree::StoreCredit < Spree::PaymentSource
   ADJUSTMENT_ACTION = 'adjustment'
   INVALIDATE_ACTION = 'invalidate'
 
-  belongs_to :user, class_name: Spree::UserClassHandle.new
-  belongs_to :created_by, class_name: Spree::UserClassHandle.new
-  belongs_to :category, class_name: "Spree::StoreCreditCategory"
-  belongs_to :credit_type, class_name: 'Spree::StoreCreditType', foreign_key: 'type_id'
+  belongs_to :user, class_name: Spree::UserClassHandle.new, optional: true
+  belongs_to :created_by, class_name: Spree::UserClassHandle.new, optional: true
+  belongs_to :category, class_name: "Spree::StoreCreditCategory", optional: true
+  belongs_to :credit_type, class_name: 'Spree::StoreCreditType', foreign_key: 'type_id', optional: true
   has_many :store_credit_events
 
   validates_presence_of :user_id, :category_id, :type_id, :created_by_id, :currency
diff --git a/core/app/models/spree/store_credit_event.rb b/core/app/models/spree/store_credit_event.rb
index 07c0294337d..02dda397a06 100644
--- a/core/app/models/spree/store_credit_event.rb
+++ b/core/app/models/spree/store_credit_event.rb
@@ -10,9 +10,9 @@ class StoreCreditEvent < Spree::Base
     include Discard::Model
     self.discard_column = :deleted_at
 
-    belongs_to :store_credit
-    belongs_to :originator, polymorphic: true
-    belongs_to :store_credit_reason, class_name: 'Spree::StoreCreditReason', inverse_of: :store_credit_events
+    belongs_to :store_credit, optional: true
+    belongs_to :originator, polymorphic: true, optional: true
+    belongs_to :store_credit_reason, class_name: 'Spree::StoreCreditReason', inverse_of: :store_credit_events, optional: true
 
     validates_presence_of :store_credit_reason, if: :action_requires_reason?
 
diff --git a/core/app/models/spree/store_payment_method.rb b/core/app/models/spree/store_payment_method.rb
index 64efc2ad34e..f1b0b0b177c 100644
--- a/core/app/models/spree/store_payment_method.rb
+++ b/core/app/models/spree/store_payment_method.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class StorePaymentMethod < Spree::Base
-    belongs_to :store, inverse_of: :store_payment_methods
-    belongs_to :payment_method, inverse_of: :store_payment_methods
+    belongs_to :store, inverse_of: :store_payment_methods, optional: true
+    belongs_to :payment_method, inverse_of: :store_payment_methods, optional: true
   end
 end
diff --git a/core/app/models/spree/store_shipping_method.rb b/core/app/models/spree/store_shipping_method.rb
index b8578c3aa0d..b98e9dacf55 100644
--- a/core/app/models/spree/store_shipping_method.rb
+++ b/core/app/models/spree/store_shipping_method.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class StoreShippingMethod < Spree::Base
-    belongs_to :store, inverse_of: :store_shipping_methods
-    belongs_to :shipping_method, inverse_of: :store_shipping_methods
+    belongs_to :store, inverse_of: :store_shipping_methods, optional: true
+    belongs_to :shipping_method, inverse_of: :store_shipping_methods, optional: true
   end
 end
diff --git a/core/app/models/spree/tax_rate.rb b/core/app/models/spree/tax_rate.rb
index 427aeaaf6ff..b113ac6c1b4 100644
--- a/core/app/models/spree/tax_rate.rb
+++ b/core/app/models/spree/tax_rate.rb
@@ -17,7 +17,7 @@ class TaxRate < Spree::Base
     include Spree::CalculatedAdjustments
     include Spree::AdjustmentSource
 
-    belongs_to :zone, class_name: "Spree::Zone", inverse_of: :tax_rates
+    belongs_to :zone, class_name: "Spree::Zone", inverse_of: :tax_rates, optional: true
 
     has_many :tax_rate_tax_categories,
       class_name: 'Spree::TaxRateTaxCategory',
diff --git a/core/app/models/spree/tax_rate_tax_category.rb b/core/app/models/spree/tax_rate_tax_category.rb
index 6f8270391d2..e68f89c7ac7 100644
--- a/core/app/models/spree/tax_rate_tax_category.rb
+++ b/core/app/models/spree/tax_rate_tax_category.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class TaxRateTaxCategory < Spree::Base
-    belongs_to :tax_rate, class_name: 'Spree::TaxRate', inverse_of: :tax_rate_tax_categories
-    belongs_to :tax_category, class_name: 'Spree::TaxCategory', inverse_of: :tax_rate_tax_categories
+    belongs_to :tax_rate, class_name: 'Spree::TaxRate', inverse_of: :tax_rate_tax_categories, optional: true
+    belongs_to :tax_category, class_name: 'Spree::TaxCategory', inverse_of: :tax_rate_tax_categories, optional: true
   end
 end
diff --git a/core/app/models/spree/unit_cancel.rb b/core/app/models/spree/unit_cancel.rb
index d54c78ac614..1b4bbf947fc 100644
--- a/core/app/models/spree/unit_cancel.rb
+++ b/core/app/models/spree/unit_cancel.rb
@@ -7,7 +7,7 @@ class Spree::UnitCancel < Spree::Base
   SHORT_SHIP = 'Short Ship'
   DEFAULT_REASON = 'Cancel'
 
-  belongs_to :inventory_unit
+  belongs_to :inventory_unit, optional: true
   has_one :adjustment, as: :source, dependent: :destroy
 
   validates :inventory_unit, presence: true
diff --git a/core/app/models/spree/user_address.rb b/core/app/models/spree/user_address.rb
index b060aea55c6..3e60b46fd82 100644
--- a/core/app/models/spree/user_address.rb
+++ b/core/app/models/spree/user_address.rb
@@ -2,8 +2,8 @@
 
 module Spree
   class UserAddress < Spree::Base
-    belongs_to :user, class_name: UserClassHandle.new, foreign_key: "user_id"
-    belongs_to :address, class_name: "Spree::Address"
+    belongs_to :user, class_name: UserClassHandle.new, foreign_key: "user_id", optional: true
+    belongs_to :address, class_name: "Spree::Address", optional: true
 
     validates_uniqueness_of :address_id, scope: :user_id
     validates_uniqueness_of :user_id, conditions: -> { active.default }, message: :default_address_exists, if: :default?
diff --git a/core/app/models/spree/user_stock_location.rb b/core/app/models/spree/user_stock_location.rb
index b627a0df9b1..c3c92d595b5 100644
--- a/core/app/models/spree/user_stock_location.rb
+++ b/core/app/models/spree/user_stock_location.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class UserStockLocation < Spree::Base
-    belongs_to :user, class_name: Spree::UserClassHandle.new, inverse_of: :user_stock_locations
-    belongs_to :stock_location, class_name: "Spree::StockLocation", inverse_of: :user_stock_locations
+    belongs_to :user, class_name: Spree::UserClassHandle.new, inverse_of: :user_stock_locations, optional: true
+    belongs_to :stock_location, class_name: "Spree::StockLocation", inverse_of: :user_stock_locations, optional: true
   end
 end
diff --git a/core/app/models/spree/variant.rb b/core/app/models/spree/variant.rb
index e41f269795c..b0b18b0d393 100644
--- a/core/app/models/spree/variant.rb
+++ b/core/app/models/spree/variant.rb
@@ -37,7 +37,7 @@ class Variant < Spree::Base
     include Spree::DefaultPrice
 
     belongs_to :product, -> { with_deleted }, touch: true, class_name: 'Spree::Product', inverse_of: :variants, optional: false
-    belongs_to :tax_category, class_name: 'Spree::TaxCategory'
+    belongs_to :tax_category, class_name: 'Spree::TaxCategory', optional: true
 
     delegate :name, :description, :slug, :available_on, :shipping_category_id,
              :meta_description, :meta_keywords, :shipping_category,
diff --git a/core/app/models/spree/variant_property_rule.rb b/core/app/models/spree/variant_property_rule.rb
index e41f06a97da..ff6bb376a88 100644
--- a/core/app/models/spree/variant_property_rule.rb
+++ b/core/app/models/spree/variant_property_rule.rb
@@ -13,7 +13,7 @@
 # targeted by the rule, the properties will automatically apply to the variant.
 module Spree
   class VariantPropertyRule < Spree::Base
-    belongs_to :product, touch: true
+    belongs_to :product, touch: true, optional: true
 
     has_many :values, class_name: 'Spree::VariantPropertyRuleValue', dependent: :destroy
     has_many :properties, through: :values
diff --git a/core/app/models/spree/variant_property_rule_condition.rb b/core/app/models/spree/variant_property_rule_condition.rb
index de03c78dfe4..7670d842a0a 100644
--- a/core/app/models/spree/variant_property_rule_condition.rb
+++ b/core/app/models/spree/variant_property_rule_condition.rb
@@ -2,8 +2,8 @@
 
 module Spree
   class VariantPropertyRuleCondition < Spree::Base
-    belongs_to :option_value
-    belongs_to :variant_property_rule, touch: true
+    belongs_to :option_value, optional: true
+    belongs_to :variant_property_rule, touch: true, optional: true
 
     validates_uniqueness_of :option_value_id, scope: :variant_property_rule_id
   end
diff --git a/core/app/models/spree/variant_property_rule_value.rb b/core/app/models/spree/variant_property_rule_value.rb
index 44c3de9595d..d030841cd55 100644
--- a/core/app/models/spree/variant_property_rule_value.rb
+++ b/core/app/models/spree/variant_property_rule_value.rb
@@ -6,7 +6,7 @@ class VariantPropertyRuleValue < Spree::Base
 
     acts_as_list scope: :variant_property_rule
 
-    belongs_to :property
-    belongs_to :variant_property_rule, touch: true
+    belongs_to :property, optional: true
+    belongs_to :variant_property_rule, touch: true, optional: true
   end
 end
diff --git a/core/app/models/spree/wallet_payment_source.rb b/core/app/models/spree/wallet_payment_source.rb
index d79e0e2d907..16f5f298c3d 100644
--- a/core/app/models/spree/wallet_payment_source.rb
+++ b/core/app/models/spree/wallet_payment_source.rb
@@ -2,8 +2,8 @@
 
 module Spree
   class WalletPaymentSource < Spree::Base
-    belongs_to :user, class_name: Spree::UserClassHandle.new, foreign_key: 'user_id', inverse_of: :wallet_payment_sources
-    belongs_to :payment_source, polymorphic: true, inverse_of: :wallet_payment_sources
+    belongs_to :user, class_name: Spree::UserClassHandle.new, foreign_key: 'user_id', inverse_of: :wallet_payment_sources, optional: true
+    belongs_to :payment_source, polymorphic: true, inverse_of: :wallet_payment_sources, optional: true
 
     validates_presence_of :user
     validates_presence_of :payment_source
diff --git a/core/app/models/spree/zone_member.rb b/core/app/models/spree/zone_member.rb
index 17e9f9aece4..a2ac6f63d68 100644
--- a/core/app/models/spree/zone_member.rb
+++ b/core/app/models/spree/zone_member.rb
@@ -2,8 +2,8 @@
 
 module Spree
   class ZoneMember < Spree::Base
-    belongs_to :zone, class_name: 'Spree::Zone', counter_cache: true, inverse_of: :zone_members
-    belongs_to :zoneable, polymorphic: true
+    belongs_to :zone, class_name: 'Spree::Zone', counter_cache: true, inverse_of: :zone_members, optional: true
+    belongs_to :zoneable, polymorphic: true, optional: true
 
     delegate :name, to: :zoneable, allow_nil: true
   end