join_scope

# File activerecord/lib/active_record/reflection.rb, line 193
      def join_scope(table, foreign_table, foreign_klass)
        predicate_builder = predicate_builder(table)
        scope_chain_items = join_scopes(table, predicate_builder)
        klass_scope       = klass_join_scope(table, predicate_builder)

        if type
          klass_scope.where!(type => foreign_klass.polymorphic_name)
        end

        scope_chain_items.inject(klass_scope, &:merge!)

        primary_key_column_names = Array(join_primary_key)
        foreign_key_column_names = Array(join_foreign_key)

        primary_foreign_key_pairs = primary_key_column_names.zip(foreign_key_column_names)

        primary_foreign_key_pairs.each do |primary_key_column_name, foreign_key_column_name|
          klass_scope.where!(table[primary_key_column_name].eq(foreign_table[foreign_key_column_name]))
        end

        if klass.finder_needs_type_condition?
          klass_scope.where!(klass.send(:type_condition, table))
        end

        klass_scope
      end