Rails - Multiple Index Key Association

Question

There seem to be a number of ways to handle a multiple foreign key association. Each way I have approached this has their draw backs, and as I am new to Rails I am convinced

Answer 1

I did find the solution to this, however it turned out I was probably asking the wrong question. I have not found away to have multiple index keys as I asked without implementing some custom sql which breaks different rails helpers.

I guess my question still stands, but how I did resolve this was to look at the problem differently. I just created the associations as they are:

belongs_to :rcvd_person, :class_name => 'Person', :foreign_key => :rcvd_id
belongs_to :origin_person, :class_name => 'Person', :foreign_key => :origin_id

And a custom sql statement:

class Person...
  has_many :links, :finder_sql => 'SELECT * FROM links WHERE origin_id = #{id} OR rcvd_id = #{id}'
end

Then I was able to manipulate the records how I wanted in my view. In case anyone else is doing something similar, I did:

<% person.links.each do |link| %> 

  <% if link.origin_id == person.id %>
    <%= link.rcvd_person.given_name %>
  <% else %>
    <%= link.origin_person.given_name %>
  <% end  %>

<% end %>

Answer 2

I'm not sure you can really support an association with multiple keys in the same table because Rails won't know which key to set if you attempt to create a relationship.

However, if you just want person.links, Rails 3 provides a way that is better than :finder_sql

class Link
  def self.by_person(person)
    where("origin_id => :person_id OR rcvd_id => :person_id", :person_id => person.id
  end 
end

class Person < ActiveRecord::Base
  # You can include the has_many relationships if you want, or not

  def links
    Link.by_person(self)
  end 
end

This lets you do things like @person.links.limit(3) (which currently appears to be broken when using :finder_sql)