Raise an error for has_one associations which try to go :through a polymorphic association [#17263]

2 files changed, 7 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 12ca3a48a9..8911506694 100644
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -46,6 +46,12 @@ module ActiveRecord
     end
   end
 
+  class HasOneAssociationPolymorphicThroughError < ActiveRecordError #:nodoc:
+    def initialize(owner_class_name, reflection)
+      super("Cannot have a has_one :through association '#{owner_class_name}##{reflection.name}' which goes through the polymorphic association '#{owner_class_name}##{reflection.through_reflection.name}'.")
+    end
+  end
+
   class HasManyThroughSourceAssociationNotFoundError < ActiveRecordError #:nodoc:
     def initialize(reflection)
       through_reflection      = reflection.through_reflection
diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index 6b5a592ee5..cff70511f5 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -821,6 +821,7 @@ module ActiveRecord
         end
 
         if through_reflection.polymorphic?
+          raise HasOneAssociationPolymorphicThroughError.new(active_record.name, self) if has_one?
           raise HasManyThroughAssociationPolymorphicThroughError.new(active_record.name, self)
         end