ruby on rails - Hard time creating a class scope for HABTM relation -

this simplified situation:

class producer   has_and_belongs_to_many :rules end  class rule   has_and_belongs_to_many :producers end 

but rule happens follow sti structure. have this:

class producer   has_and_belongs_to_many :rules    has_and_belongs_to_many :product_rules, join_table: :producers_rules,     association_foreign_key: :rule_id    has_and_belongs_to_many :fee_rules, join_table: :producers_rules     association_foreign_key: :rule_id end  class rule   has_and_belongs_to_many :producers end  class productrule < rule end  class feerule < rule end 

no big deal, works out fine. want create scope returns producers related productrules

something equivalent this:

producer.all.select{|x| x.product_rules.any? } 

can point out quick solution?

note: obvioulsy don't want load producers , select them afterward, want directly load right ones

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update

im using rails version 2.3.15

every association between producer , 1 of rule's subclasses going create separate record on join table. can use fact , select producers have record on join table pointing them (taking care select correct type):

in rails 2.x:

class producer   def self.with_some_product_rule     scoped(conditions: <<-sql)       producers.id in (         select producer_id producers_rules         inner join rules on rules.id = producers_rules.rule_id         rules.type = 'productrule'       )     sql   end end