ARRGH! Unconventional tables and RoR

I think this should be:

class FrogPair < ActiveRecord::Base
belongs_to :friend, :class_name=>‘Frog’, :foreign_key=>‘species_friend’

belongs_to :foe, :class_name=>‘Frog’, :foreign_key=>‘species_foe’

That allows you to do

fp = FrogPair.find(2)
and then

If you want access to a list of pairs where a specific frog is the friend or foe respectively, do:

class Frog < ActiveRecord::Base
has_many :pairs_as_friend, :class_name=>‘FrogPair’, :foreign_key=>‘species_friend’

has_many :pairs_as_friend, :class_name=>‘FrogPair’, :foreign_key=>‘species_foe’

Thinking of it, I think you have the semantics of your data model wrong. If you want to express relationships between different frog species, you are better off separating it into two different tables:


where FrogFriends and FrogFoes may look something like this:

frog_id friend_id
frog_id foe_id

The common problem with these reciprocal relationships is that you will probably have to insert two records into each of the tables:

some_frog_species_instance.add_friend( another_frog_species_instance )
should result in two “friend” entries, with the values reversed, so you can find all friends of a certain species by the condition “FROM frog_friends WHERE frog_id = some_frog_species_id”, rather than “FROM frog_friends WHERE frog_id=some_frog_species_id OR friend_id=some_frog_species_id”