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Single Table Inheritance, Polymorphic association (self-referential and normal) bug

#2601

I used single table inheritance and self-referential polymorphic association in some models and the wrong sql was generated. I have


class Feeling < ActiveRecord::Base
  belongs_to :feelable, :polymorphic => true
  belongs_to :feeler, :polymorphic => true
end

class PersonalFeeling < Feeling
  has_many :feeling_comments, :as => :feelable, :dependent => :destroy
end


class FeelingComment < Feeling

end

and 'feelings' table in the database which has the type attribute. STI works just fine in the sense that if I create a Feeling type is set to Feeling, PersonalFeeling type is set to PersonalFeeling and so on.

If I run the following code


pf = PersonalFeeling.first
comments = pf.feeling_comments

The generated SQL is


SELECT * FROM `feelings` WHERE (`feelings`.feelable_id = 14 AND `feelings`.feelable_type = 'Feeling') AND ( (`feelings`.`type` = 'FeelingComment' ) )

which is not correct. The feelings.feelable_type = 'Feeling' should have been feelings.feelable_type = 'PersonalFeeling'.

I tracked the issue to the lib\active_record\associations\has_many_association.rb on line 91 in the construct_sql method. The issue is that the line "#{@reflection.quoted_table_name}.#{@reflection.options[:as]}type = #{@owner.class.quote_value(@owner.class.base_class.name.to_s)}" is trying setting the type to the base_class which is not correct in this case. I don't know why the behavior of using the base_class instead of the @owner's class itself.

After finding that cause, I also tried the case with non self-referential and the bug still exists.

Reported by humanzz · May 2nd, 2009 @ 02:34 PM

Activity

Iain Adams
Am I right in thinking that the API documentation is wrong on this issue as well.

It claims that having a polymorphic_type=(sType) method should work, but it won't work for me.

From the API......

class Asset < ActiveRecord::Base
```
belongs_to :attachable, :polymorphic => true

def attachable_type=(sType)
   raise "Setting type"
end
```
end

class Post < ActiveRecord::Base
```
# because we store "Post" in attachable_type now :dependent => :destroy will work
has_many :assets, :as => :attachable, :dependent => :destroy
```
end

class GuestPost < Post end

class MemberPost < Post end

The method attachable_type=(sType) is never even used otherwise I would get an error....right?
May 8th, 2009 @ 05:49 PM
Matt Jones
A couple things:
- does the "bad SQL" get the right answer?
- in this case, you don't actually need a polymorphic association. If the models you're associating are all STI subclasses, you can just use regular has_many and friends. The polymorphic stuff comes in where you have objects in the association that aren't even part of the same DB table.
June 8th, 2009 @ 09:19 PM
PommyTom
I'm also getting this error. For the exact same reasoning as the poster.

Forcibly overriding the _type field on the relationship to still have access to the has_many/named_scopes

November 19th, 2009 @ 03:10 AM
Matt Jones
- State changed from new to wontfix
This is not a bug - the _type field essentially points to the base class. Note that the two statements below are equivalent:
```
Feeling.find(14) # => PersonalFeeling id 14

PersonalFeeling.find(14) # => PersonalFeeling id 14
```
Closing for now - if anyone can write a test where the existing code returns incorrect results (in other words, finds the wrong records) we can re-examine this.
November 19th, 2009 @ 09:34 PM