has and belongs to many - How can I join the same 2 models twice in Rails? -

i have app country preferences. user have 2 types of country preferences - event , research. in future there may more. leaning more towards having 2 tables represent on using sti. i'm having bit of trouble configuring rails elegantly this. hack rather rails convention. want this:

class user < activerecord::base   has_many event_countries, :through => :event_countries, :class_name => 'country'   has_many research_countries, :through => :research_countries, :class_name => 'country' end  class eventcountry < activerecord::base   belongs_to :country   belongs_to :user end  class researchcountry < activerecord::base   belongs_to :country   belongs_to :user end  class country < activerecord::base ... end 

this doesn't work though. given "pseudo code" know how implement in rails?

i think you're going declaring them wrong, because should work properly. that's :through directive for:

class user < activerecord::base   has_many :event_countries   has_many :countries_with_events,     :through => :event_countries,     :source => :country    has_many :research_countries   has_many :countries_with_researches,     :through => :research_countries,     :source => :country end  class eventcountry < activerecord::base   belongs_to :country   belongs_to :user end  class researchcountry < activerecord::base   belongs_to :country   belongs_to :user end  class country < activerecord::base   # ... end 

a lot of awkwardness comes labels you've chosen tables. although they'd seem reasonable @ first glance, way use them ends making them difficult.

you might want call research_countries user_research_countries relationship name can user.research_countries :through:

class user < activerecord::base   has_many :user_event_countries   has_many :event_countries,     :through => :user_event_countries,     :source => :country    has_many :user_research_countries   has_many :research_countries,     :through => :user_research_countries,     :source => :country end  class usereventcountry < activerecord::base   belongs_to :country   belongs_to :user end  class userresearchcountry < activerecord::base   belongs_to :country   belongs_to :user end  class country < activerecord::base   # ... end 

you can refactor further adding field user-country association table includes 1 or more flags, in case research or event or whatever require later:

class user < activerecord::base   has_many :user_countries   has_many :event_countries,     :through => :user_countries,     :source => :country,     :conditions => { :event => true }   has_many :research_countries,     :through => :user_countries,     :source => :country,     :conditions => { :research => true } end  class usercountry < activerecord::base   belongs_to :country   belongs_to :user    # * column :event, :boolean   # * column :research, :boolean end  class country < activerecord::base   # ... end