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.

9 files changed, 63 insertions, 4 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index f1a5e58da6..e987a0e279 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,8 @@
+*   Set polymorphic type column to NULL on `dependent: :nullify` strategy. 
+    
+    On polymorphic associations both the foreign key and the foreign type columns will be set to NULL.
+    
+    *Laerti Papa*
 
 *   Allow `ActionController::Params` as argument of `ActiveRecord::Base#exists?`.
 
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
diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index 5921193374..4b9b55f822 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -1815,6 +1815,22 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal num_accounts, Account.count
   end
 
+  def test_depends_and_nullify_on_polymorphic_assoc
+    author = PersonWithPolymorphicDependentNullifyComments.create!(first_name: "Laertis")
+    comment = posts(:welcome).comments.first
+    comment.author = author
+    comment.save!
+
+    assert_equal comment.author_id, author.id
+    assert_equal comment.author_type, author.class.name
+
+    author.destroy
+    comment.reload
+
+    assert_nil comment.author_id
+    assert_nil comment.author_type
+  end
+
   def test_restrict_with_exception
     firm = RestrictedWithExceptionFirm.create!(name: "restrict")
     firm.companies.create(name: "child")
diff --git a/activerecord/test/cases/associations/has_one_associations_test.rb b/activerecord/test/cases/associations/has_one_associations_test.rb
index bf574f6637..3e5b5c1275 100644
--- a/activerecord/test/cases/associations/has_one_associations_test.rb
+++ b/activerecord/test/cases/associations/has_one_associations_test.rb
@@ -12,6 +12,9 @@ require "models/bulb"
 require "models/author"
 require "models/image"
 require "models/post"
+require "models/drink_designer"
+require "models/chef"
+require "models/department"
 
 class HasOneAssociationsTest < ActiveRecord::TestCase
   self.use_transactional_tests = false unless supports_savepoints?
@@ -114,6 +117,21 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
     assert_nil Account.find(old_account_id).firm_id
   end
 
+  def test_nullify_on_polymorphic_association
+    department = Department.create!
+    designer = DrinkDesignerWithPolymorphicDependentNullifyChef.create!
+    chef = department.chefs.create!(employable: designer)
+
+    assert_equal chef.employable_id, designer.id
+    assert_equal chef.employable_type, designer.class.name
+
+    designer.destroy!
+    chef.reload
+
+    assert_nil chef.employable_id
+    assert_nil chef.employable_type
+  end
+
   def test_nullification_on_destroyed_association
     developer = Developer.create!(name: "Someone")
     ship = Ship.create!(name: "Planet Caravan", developer: developer)
diff --git a/activerecord/test/models/drink_designer.rb b/activerecord/test/models/drink_designer.rb
index eb6701b84e..8258408f35 100644
--- a/activerecord/test/models/drink_designer.rb
+++ b/activerecord/test/models/drink_designer.rb
@@ -4,5 +4,11 @@ class DrinkDesigner < ActiveRecord::Base
   has_one :chef, as: :employable
 end
 
+class DrinkDesignerWithPolymorphicDependentNullifyChef < ActiveRecord::Base
+  self.table_name = "drink_designers"
+
+  has_one :chef, as: :employable, dependent: :nullify
+end
+
 class MocktailDesigner < DrinkDesigner
 end
diff --git a/activerecord/test/models/person.rb b/activerecord/test/models/person.rb
index 5cba1e440e..c3d15a571a 100644
--- a/activerecord/test/models/person.rb
+++ b/activerecord/test/models/person.rb
@@ -62,6 +62,11 @@ class PersonWithDependentNullifyJobs < ActiveRecord::Base
   has_many :jobs, source: :job, through: :references, dependent: :nullify
 end
 
+class PersonWithPolymorphicDependentNullifyComments < ActiveRecord::Base
+  self.table_name = "people"
+  has_many :comments, as: :author, dependent: :nullify
+end
+
 class LoosePerson < ActiveRecord::Base
   self.table_name = "people"
   self.abstract_class = true