# Crazy @@subclasses magic and ActiveRecord

**URL:** <https://www.ruby-forum.com/t/crazy-subclasses-magic-and-activerecord/132568>\
**Category:** Rails\
**Created:** [March 21, 2008, 3:10pm UTC](https://www.ruby-forum.com/t/crazy-subclasses-magic-and-activerecord/132568 "2008-03-21T15:10:37Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Kevin\_Wu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/d78d45/32.png) [@Kevin\_Wu](https://www.ruby-forum.com/u/Kevin_Wu)\
**Post date:** [March 21, 2008, 3:10pm UTC](https://www.ruby-forum.com/t/crazy-subclasses-magic-and-activerecord/132568/1 "2008-03-21T15:10:37Z")

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## I’m experiencing this exact behavior using STI

[http://www.techlists.org/archives/programming/railslist/2005-12/msg00202.shtml](http://www.techlists.org/archives/programming/railslist/2005-12/msg00202.shtml)  
Here’s a concrete example. Say I have three classes that inherit  
from  
ActiveRecord, and I have one instance of each in my ‘animals’ table:  
Dog \< Mammal \< Animal \< ActiveRecord::Base

Run these command in order and you get:  
Mammal.count() = 1  
Dog.count() = 1  
Mammal.count() = 2!

## Here’s the SQL: SHOW FIELDS FROM animals SELECT COUNT(_) FROM animals WHERE ( (animals.`type` = ‘Mammal’ ) ) SHOW FIELDS FROM animals SELECT COUNT(_) FROM animals WHERE ( (animals.`type` = ‘Dog’ ) ) SELECT COUNT(\*) FROM animals WHERE ( (animals.`type` = ‘Mammal’ OR animals.`type` = ‘Dog’ ) )

I noticed what’s making this happen is the ActiveRecord::Base  
@@subclasses class variable handled by this attribute.  
def subclasses  
@@subclasses[self] ||= []  
@@subclasses[self] + extra =  
@@subclasses[self].inject([]) {|list, subclass| list |  
subclass.subclasses }  
end

Is there a way to “eager load” this variable with @@subclasses[Mammel]  
= [Dog] so that whenever I do Mammel.find(:all), I’m also retrieving  
records with Dog?

I could switch to polymorphic and it would probably make my  
application more scalable, but I’d prefer to stay on one table to  
maintain simplicity. This is madness and my head hurts. Anyone have  
any suggestions?

Thanks

Kevin

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<div class="post-metadata">

**Author:** ![Kevin\_Wu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/d78d45/32.png) [@Kevin\_Wu](https://www.ruby-forum.com/u/Kevin_Wu)\
**Post date:** [March 24, 2008, 12:10pm UTC](https://www.ruby-forum.com/t/crazy-subclasses-magic-and-activerecord/132568/2 "2008-03-24T12:10:04Z")

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Dude man! Thanks SOOOOO MUCH.  
I added require\_dependency ‘model’  
see the bottom of  
[http://wiki.rubyonrails.org/rails/pages/SingleTableInheritance](http://wiki.rubyonrails.org/rails/pages/SingleTableInheritance)

- DOH! if only I read that more closely.

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<div class="post-metadata">

**Author:** ![Kevin\_Wu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/d78d45/32.png) [@Kevin\_Wu](https://www.ruby-forum.com/u/Kevin_Wu)\
**Post date:** [March 21, 2008, 3:47pm UTC](https://www.ruby-forum.com/t/crazy-subclasses-magic-and-activerecord/132568/3 "2008-03-21T15:47:53Z")

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Are the subclasses in the same file as the base class? If not,  
‘require’ or ‘load’ might do the trick.