# Comparing polymorphic property to same object fails **URL:** \ **Category:** Rails\ **Created:** [May 6, 2007, 9:15am UTC](https://www.ruby-forum.com/t/comparing-polymorphic-property-to-same-object-fails/103453 "2007-05-06T09:15:07Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Gisborne](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/dc4da7/32.png) [@Gisborne](https://www.ruby-forum.com/u/Gisborne)\ **Post date:** [May 6, 2007, 9:15am UTC](https://www.ruby-forum.com/t/comparing-polymorphic-property-to-same-object-fails/103453/1 "2007-05-06T09:15:07Z")
I’ve got a polymorphic association on one table. I assign to it in the controller. This is handling invitations of users to tasks in a task management application. If the user issuing the invitation is the user being invited (ie the user assigned themselves to a task), I want to activate the invitation immediately in the model. The trouble is that this: ``` if self.assignable == self.created_by self.activated_at = Time.now self.activation_code = nil end ``` fails to detect equality correctly. I’ve tried ===, eql? etc. When I look at . **id** when I know that I set assignable equal to created\_by, the values are different (wildly so; one is like 4 and the other is a five digit number or something). I’m guessing Rails handles polymorphic associations via a proxy object or something. So the question is: how do I do this comparison? ---
**Author:** ![Gisborne](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/dc4da7/32.png) [@Gisborne](https://www.ruby-forum.com/u/Gisborne)\ **Post date:** [May 6, 2007, 4:54pm UTC](https://www.ruby-forum.com/t/comparing-polymorphic-property-to-same-object-fails/103453/2 "2007-05-06T16:54:46Z")
You can get the underlying object from the proxy calling #target or #proxy\_target. That should allow you to compare the object ids directly. But why not compare the #id (eg, the actual primary key of the users table) of both assignable and created\_by. This is safer especially if activerecord decides load created\_by and assignable into two different objects which is probably very likely. ---
**Author:** ![Gisborne](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/dc4da7/32.png) [@Gisborne](https://www.ruby-forum.com/u/Gisborne)\ **Post date:** [May 6, 2007, 6:45pm UTC](https://www.ruby-forum.com/t/comparing-polymorphic-property-to-same-object-fails/103453/3 "2007-05-06T18:45:56Z")
On May 6, 9:54 am, eden li [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > You can get the underlying object from the proxy calling #target or > #proxy\_target. That should allow you to compare the object ids > directly. > > But why not compare the #id (eg, the actual primary key of the users > table) of both assignable and created\_by. This is safer especially if > activerecord decides load created\_by and assignable into two different > objects which is probably very likely. The problem with comparing just the ids is if the polymorphic association is to a different table (ie to a different class), to an object that happens to have the same id in that other table. Unfortunate that if this is documented anywhere, it’s carefully hidden. ☹ Thanks. ---
**Author:** ![Gisborne](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/dc4da7/32.png) [@Gisborne](https://www.ruby-forum.com/u/Gisborne)\ **Post date:** [May 7, 2007, 12:47am UTC](https://www.ruby-forum.com/t/comparing-polymorphic-property-to-same-object-fails/103453/4 "2007-05-07T00:47:28Z")
On May 6, 9:54 am, eden li [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > You can get the underlying object from the proxy calling #target or > #proxy\_target. That should allow you to compare the object ids > directly. This doesn’t work. Changing the code to: ``` if self.assignable.target == self.created_by self.activated_at = Time.now self.activation_code = nil end ``` fails. As does using assignable.proxy\_target. Anyone know how to get this working? ---
**Author:** ![Gisborne](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/dc4da7/32.png) [@Gisborne](https://www.ruby-forum.com/u/Gisborne)\ **Post date:** [May 7, 2007, 3:07am UTC](https://www.ruby-forum.com/t/comparing-polymorphic-property-to-same-object-fails/103453/5 "2007-05-07T03:07:35Z")
On May 6, 5:46 pm, Gisborne [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > ``` > self.activation_code = nil > end > > ``` > > fails. As does using assignable.proxy\_target. > > Anyone know how to get this working? Whoops. Turns out it works fine and I was just being a complete moron. Thanks for the help. ---
**Author:** ![Gisborne](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/dc4da7/32.png) [@Gisborne](https://www.ruby-forum.com/u/Gisborne)\ **Post date:** [May 7, 2007, 5:02am UTC](https://www.ruby-forum.com/t/comparing-polymorphic-property-to-same-object-fails/103453/6 "2007-05-07T05:02:40Z")
On May 7, 12:44 am, Gisborne [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > The problem with comparing just the ids is if the polymorphic > association is to a different table (ie to a different class), to an > object that happens to have the same id in that other table. Maybe I misunderstand your schema, but after retrieving “assignable” you should get a proper user object. The polymorphic association will retrieve the object from the right table for you. This is one of the reasons you need an :assignable\_type column. > Unfortunate that if this is documented anywhere, it’s carefully > hidden. ☹ The association proxies are in the guts of ActiveRecord. I assume it’s not well documented because rails-core wants to be able to make massive changes to it between releases. Anyway, you only need to deal with them if you’re relying on strict ruby object semantics.