# How to describe self join in a model

**URL:** <https://www.ruby-forum.com/t/how-to-describe-self-join-in-a-model/155071>\
**Category:** Rails\
**Created:** [December 7, 2008, 11:38am UTC](https://www.ruby-forum.com/t/how-to-describe-self-join-in-a-model/155071 "2008-12-07T11:38:36Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![ali](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/8c91f0/32.png) [@ali](https://www.ruby-forum.com/u/ali)\
**Post date:** [December 7, 2008, 11:38am UTC](https://www.ruby-forum.com/t/how-to-describe-self-join-in-a-model/155071/1 "2008-12-07T11:38:36Z")

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Hi ,  
I am new to rails, and i need to know one thing, i have a table  
called Categories and i want to self join it in such a way , that one  
category could be a parent of many categories, but could be child of  
only one category.

Please tell me how to tell rails , in my Category Model, does the  
following work for me ?

class Category

belongs\_to :category  
has\_many :categories

end

---

<div class="post-metadata">

**Author:** ![ali](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/8c91f0/32.png) [@ali](https://www.ruby-forum.com/u/ali)\
**Post date:** [December 7, 2008, 4:51pm UTC](https://www.ruby-forum.com/t/how-to-describe-self-join-in-a-model/155071/2 "2008-12-07T16:51:07Z")

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:acts\_as\_tree: [http://wiki.rubyonrails.org/rails/pages/ActsAsTree](http://wiki.rubyonrails.org/rails/pages/ActsAsTree)