ruby - find_or_create_by on intermediate table in rails 2.3 -

i have 2 tables , related third table follows.

class < activerecord::base   has_many :b, :through => :ab   has_many :ab end  class b < activerecord::base   has_many :a, :through => :ab   has_many :ab end  class ab < activerecord::base   belongs_to :b,   belongs_to :a end 

i want able insert intermediate table(ab), using find_or_create.but find_or_create doesnot work on ab. how can it, other finding , creating seperately ??

ps: dont want use has_and_belongs_to_many because doesnot create intermediate model , want insert intermediate table without creating rows in end tables, , b.

some suggestions please??

find_or_create_by has been added in rails 4. can write (should go initializers):

class activerecord::base   def self.find_by(params)     scoped.where(params).limit(1).first   end    def self.find_or_create_by(params)     find_by(params) || create(params)   end end