Refs #28025 nullify *_type column on polymorphic associations on :nu… (#28078)

This PR addresses the issue described in #28025. On `dependent: :nullify` strategy only the foreign key of the relation is nullified. However on polymorphic associations the  `*_type` column is not nullified leaving the record with a NULL `*_id` but the `*_type` column is present.

4 files changed, 13 insertions, 4 deletions

diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index fb1df00dc8..7bdbd8ce69 100644
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -1293,7 +1293,8 @@ module ActiveRecord
         #
         #   * <tt>:destroy</tt> causes all the associated objects to also be destroyed.
         #   * <tt>:delete_all</tt> causes all the associated objects to be deleted directly from the database (so callbacks will not be executed).
-        #   * <tt>:nullify</tt> causes the foreign keys to be set to +NULL+. Callbacks are not executed.
+        #   * <tt>:nullify</tt> causes the foreign keys to be set to +NULL+. Polymorphic type will also be nullified
+        #     on polymorphic associations. Callbacks are not executed.
         #   * <tt>:restrict_with_exception</tt> causes an <tt>ActiveRecord::DeleteRestrictionError</tt> exception to be raised if there are any associated records.
         #   * <tt>:restrict_with_error</tt> causes an error to be added to the owner if there are any associated objects.
         #
@@ -1436,7 +1437,8 @@ module ActiveRecord
         #
         #   * <tt>:destroy</tt> causes the associated object to also be destroyed
         #   * <tt>:delete</tt> causes the associated object to be deleted directly from the database (so callbacks will not execute)
-        #   * <tt>:nullify</tt> causes the foreign key to be set to +NULL+. Callbacks are not executed.
+        #   * <tt>:nullify</tt> causes the foreign key to be set to +NULL+. Polymorphic type column is also nullified
+        #     on polymorphic associations. Callbacks are not executed.
         #   * <tt>:restrict_with_exception</tt> causes an <tt>ActiveRecord::DeleteRestrictionError</tt> exception to be raised if there is an associated record
         #   * <tt>:restrict_with_error</tt> causes an error to be added to the owner if there is an associated object
         #
diff --git a/activerecord/lib/active_record/associations/foreign_association.rb b/activerecord/lib/active_record/associations/foreign_association.rb
index 40010cde03..59af6f54c3 100644
--- a/activerecord/lib/active_record/associations/foreign_association.rb
+++ b/activerecord/lib/active_record/associations/foreign_association.rb
@@ -9,5 +9,12 @@ module ActiveRecord::Associations
         false
       end
     end
+
+    def nullified_owner_attributes
+      Hash.new.tap do |attrs|
+        attrs[reflection.foreign_key] = nil
+        attrs[reflection.type] = nil if reflection.type.present?
+      end
+    end
   end
 end
diff --git a/activerecord/lib/active_record/associations/has_many_association.rb b/activerecord/lib/active_record/associations/has_many_association.rb
index f6fdbcde54..eb22db838c 100644
--- a/activerecord/lib/active_record/associations/has_many_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_association.rb
@@ -92,7 +92,7 @@ module ActiveRecord
           if method == :delete_all
             scope.delete_all
           else
-            scope.update_all(reflection.foreign_key => nil)
+            scope.update_all(nullified_owner_attributes)
           end
         end
 
diff --git a/activerecord/lib/active_record/associations/has_one_association.rb b/activerecord/lib/active_record/associations/has_one_association.rb
index 390bfd8b08..99971286a3 100644
--- a/activerecord/lib/active_record/associations/has_one_association.rb
+++ b/activerecord/lib/active_record/associations/has_one_association.rb
@@ -33,7 +33,7 @@ module ActiveRecord
             target.destroy
             throw(:abort) unless target.destroyed?
           when :nullify
-            target.update_columns(reflection.foreign_key => nil) if target.persisted?
+            target.update_columns(nullified_owner_attributes) if target.persisted?
           end
         end
       end