ruby on rails - How can I setup a has_many associated to look in 2 columns in a db table (category_a_id and category_b_id) -

i need able link categories each other.

i have category_links table 2 columns category_a_id , category_b_id hold id of 2 categories linked.

i want able call category.find(1).category_links , grab records id 1 both category_a_id , category_b_id columns. if category destroyed delete associated records in category_link db if associated in category_a_id or category_b_id column.

currently in category_links model have

belongs_to :category_b, :class_name => :category belongs_to :category_a, :class_name => :category 

and in category db

has_many(:category_links, :foreign_key => :category_a_id, :dependent => :destroy) has_many(:category_links, :foreign_key => :category_b_id, :dependent => :destroy) 

but assosiates records category_b_id column matching id not both. calling category.find(1).category_links doesnt grab records matching both category_a_id , category_b_id. same goes destroying category.

how can work if destroy category looks both columns associated category , calling category.find(1).category_links looks in both columns matching record?

there's no simple way achieve through has_many, if don't have fancy create custom method on category:

def category_links   @category_links ||= categorylinks.where('category_a_id = ? or category_b_id = ?', id, id) end