I'm implementing a M-M relationship with a single table upon itself,
and wonder if there's anything I should look out for in rails, when
doing this. Also, what notation I would best use in Rails (I'm
I'm doing this because I have a Category model, and each category
might be "similar to" a number of other categories. So, one way of
modelling this is to have a new join table with two columns which are
both Category ids.