Rails core - Nov 2006 - Expected behaviour of polymorphic has_many relationship

Hi

I posted something similar to this on the Rails-takl list but I''ve  
just discovered the core list and Iguess this is a better place to  
ask.  I''ve been doing a bit of work on inheritance in ActiveRecord  
and my changes broke this test from associations/join_model_test.rb:

   def  
test_polymorphic_has_many_create_model_with_inheritance_and_custom_base_ 
class
     post = SubStiPost.create :title => ''SubStiPost'', :body
=>
''SubStiPost body''
     assert_instance_of SubStiPost, post

     tagging = tags(:misc).taggings.create(:taggable => post)
     assert_equal "SubStiPost", tagging.taggable_type
   end

I was getting ''<"SubStiPost"> expected but was
<"Post">''.  To fix
this I modified a line in this section of the belongs_to method in  
associations.rb:

   if reflection.options[:polymorphic]
     association_accessor_methods(reflection,  
BelongsToPolymorphicAssociation)

     module_eval do
       before_save <<-EOF
         association = instance_variable_get("@#{reflection.name}")
         if association && association.target
           if association.new_record?
             association.save(true)
           end

           if association.updated?
             self["#{reflection.primary_key_name}"] = association.id
   -         self["#{reflection.options[:foreign_type]}"] =  
association.class.base_class.name.to_s
   +         self["#{reflection.options[:foreign_type]}"] =  
association.class.name.to_s
           end
         end
       EOF
     end
   else
     ...
   end

But that change breaks these tests:

   def test_polymorphic_has_many_create_model_with_inheritance
     post = posts(:thinking)
     assert_instance_of SpecialPost, post

     tagging = tags(:misc).taggings.create(:taggable => post)
     assert_equal "Post", tagging.taggable_type
   end

   def test_polymorphic_has_one_create_model_with_inheritance
     tagging = tags(:misc).create_tagging(:taggable => posts(:thinking))
     assert_equal "Post", tagging.taggable_type
   end

Both now fail on <"Post"> expected but was
<"SpecialPost">.

What I don''t understand is that the fixture Post :thinking is  
actually a SpecialPost, so why is that not the correct taggable_type  
value?  I can''t figure out what the intended behaviour of this  
association.

I''d be really grateful for an explanation of this, it''s the
only
thing I can''t make work.

Ashley

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What are your original changes, that broke the tests initially?

Evan

On Nov 5, 12:46 pm, Ashley Moran <w...@ashleymoran.me.uk>
wrote:
> Hi
>
> I posted something similar to this on the Rails-takl list but I''ve
> just discovered the core list and Iguess this is a better place to
> ask.  I''ve been doing a bit of work on inheritance in ActiveRecord
> and my changes broke this test from associations/join_model_test.rb:
>
>    def
> test_polymorphic_has_many_create_model_with_inheritance_and_custom_base_
> class
>      post = SubStiPost.create :title => ''SubStiPost'',
:body =>
> ''SubStiPost body''
>      assert_instance_of SubStiPost, post
>
>      tagging = tags(:misc).taggings.create(:taggable => post)
>      assert_equal "SubStiPost", tagging.taggable_type
>    end
>
> I was getting ''<"SubStiPost"> expected but was
<"Post">''.  To fix
> this I modified a line in this section of the belongs_to method in
> associations.rb:
>
>    if reflection.options[:polymorphic]
>      association_accessor_methods(reflection,
> BelongsToPolymorphicAssociation)
>
>      module_eval do
>        before_save <<-EOF
>          association =
instance_variable_get("@#{reflection.name}")
>          if association && association.target
>            if association.new_record?
>              association.save(true)
>            end
>
>            if association.updated?
>              self["#{reflection.primary_key_name}"] =
association.id
>    -         self["#{reflection.options[:foreign_type]}"] >
association.class.base_class.name.to_s
>    +         self["#{reflection.options[:foreign_type]}"] >
association.class.name.to_s
>            end
>          end
>        EOF
>      end
>    else
>      ...
>    end
>
> But that change breaks these tests:
>
>    def test_polymorphic_has_many_create_model_with_inheritance
>      post = posts(:thinking)
>      assert_instance_of SpecialPost, post
>
>      tagging = tags(:misc).taggings.create(:taggable => post)
>      assert_equal "Post", tagging.taggable_type
>    end
>
>    def test_polymorphic_has_one_create_model_with_inheritance
>      tagging = tags(:misc).create_tagging(:taggable => posts(:thinking))
>      assert_equal "Post", tagging.taggable_type
>    end
>
> Both now fail on <"Post"> expected but was
<"SpecialPost">.
>
> What I don''t understand is that the fixture Post :thinking is
> actually a SpecialPost, so why is that not the correct taggable_type
> value?  I can''t figure out what the intended behaviour of this
> association.
>
> I''d be really grateful for an explanation of this, it''s
the only
> thing I can''t make work.
> 
> Ashley

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On 20 Nov 2006, at 21:41, evn wrote:
> What are your original changes, that broke the tests initially?
>
> Evan

Hi Evan

It was my attempt at class-table inheritance here: http:// 
dev.rubyonrails.org/ticket/6566

It''s not finished yet, because I haven''t made it work with  
associations, but the ONLY thing it breaks in the existing tests (ie  
if you use a CTI-enabled ActiveRecord but don''t actually use CTI) is  
polymorphic has_many relationships.  I think this is because I''ve  
redefined the meaning of "abstract class".

Any ideas?

Ashley



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