construct_join_attributes

# File activerecord/lib/active_record/associations/has_many_through_association.rb, line 97
        def construct_join_attributes(associate)
          # TODO: revist this to allow it for deletion, supposing dependent option is supported
          raise ActiveRecord::HasManyThroughCantAssociateThroughHasManyReflection.new(@owner, @reflection) if @reflection.source_reflection.macro == :has_many
          join_attributes = construct_owner_attributes(@reflection.through_reflection).merge(@reflection.source_reflection.primary_key_name => associate.id)
          if @reflection.options[:source_type]
            join_attributes.merge!(@reflection.source_reflection.options[:foreign_type] => associate.class.base_class.name.to_s)
          end
          join_attributes
        end