Add foreign key constraint point to country table

This adds database-level foreign key constraints to tables that
reference the countries table.

If trying to delete a country, and there are addresses referencing that
country, we want to restrict that. Addresses are immutable and must stay
valid.

If there are prices referencing the country, the same applies, we want
to restrict.

If the only thing holding us back from deleting a country is states, we
can delete the state records as well.

Author: mamhoff

core/db/migrate/20250709073151_add_country_foreign_keys.rb

@@ -0,0 +1,73 @@
+# frozen_string_literal: true
+
+class AddCountryForeignKeys < ActiveRecord::Migration[7.0]
+  def up
+    # Uncomment the following code to remove orphaned records if this migration fails
+    #
+    # say_with_time "Removing orphaned states (no corresponding country)" do
+    #   Spree::State.left_joins(:country).where(spree_countries: { id: nil }).delete_all
+    # end
+
+    begin
+      add_foreign_key :spree_states, :spree_countries, column: :country_id, null: false, on_delete: :cascade
+    rescue ActiveRecord::StatementInvalid => e
+      if e.cause.is_a?(PG::ForeignKeyViolation) || e.cause.is_a?(Mysql2::Error) || e.cause.is_a?(SQLite3::ConstraintException)
+        Rails.logger.warn <<~MSG
+          ⚠️ Foreign key constraint failed when adding :spree_states => :spree_countries.
+          To fix this:
+            1. Uncomment the code that removes orphaned records.
+            2. Rerun the migration.
+          Offending error: #{e.cause.class} - #{e.cause.message}
+        MSG
+      end
+      raise
+    end
+
+    # Uncomment the following code to remove orphaned records if this migration fails
+    #
+    # say_with_time "Updating orphaned addresses (no corresponding country) to use default country" do
+    #   Spree::Address.left_joins(:country).where(spree_countries: { id: nil }).update_all(country: Spree::Country.default)
+    # end
+
+    begin
+      add_foreign_key :spree_addresses, :spree_countries, column: :country_id, null: false, on_delete: :restrict
+    rescue ActiveRecord::StatementInvalid => e
+      if e.cause.is_a?(PG::ForeignKeyViolation) || e.cause.is_a?(Mysql2::Error) || e.cause.is_a?(SQLite3::ConstraintException)
+        Rails.logger.warn <<~MSG
+          ⚠️ Foreign key constraint failed when adding :spree_addresses => :spree_countries.
+          To fix this:
+            1. Uncomment the code that removes orphaned records.
+            2. Rerun the migration.
+          Offending error: #{e.cause.class} - #{e.cause.message}
+        MSG
+      end
+      raise
+    end
+    # Uncomment the following code to remove orphaned records if this migration fails
+    #
+    # say_with_time "Deleting orphaned prices (country ID without corresponding country)" do
+    #   Spree::Price.where.not(country_iso: nil).left_joins(:country).where(spree_countries: { iso: nil }).update_all(country_iso: Spree::Config.default_country_iso)
+    # end
+
+    begin
+      add_foreign_key :spree_prices, :spree_countries, column: :country_iso, primary_key: :iso, null: true, on_delete: :restrict
+    rescue ActiveRecord::StatementInvalid => e
+      if e.cause.is_a?(PG::ForeignKeyViolation) || e.cause.is_a?(Mysql2::Error) || e.cause.is_a?(SQLite3::ConstraintException)
+        Rails.logger.warn <<~MSG
+          ⚠️ Foreign key constraint failed when adding :spree_prices => :spree_countries.
+          To fix this:
+            1. Uncomment the code that removes orphaned records.
+            2. Rerun the migration.
+          Offending error: #{e.cause.class} - #{e.cause.message}
+        MSG
+      end
+      raise
+    end
+  end
+
+  def down
+    remove_foreign_key :spree_states, :spree_countries, column: :country_id, null: false, on_delete: :cascade
+    remove_foreign_key :spree_addresses, :spree_countries, column: :country_id, null: false, on_delete: :restrict
+    remove_foreign_key :spree_prices, :spree_countries, column: :country_id, null: true, on_delete: :restrict
+  end
+end