delete_records

# File activerecord/lib/active_record/associations/has_many_through_association.rb, line 140
        def delete_records(records, method)
          ensure_not_nested

          # This is unoptimised; it will load all the target records
          # even when we just want to delete everything.
          records = load_target if records == :all

          scope = through_association.scope
          scope.where! construct_join_attributes(*records)

          case method
          when :destroy
            if scope.klass.primary_key
              count = scope.destroy_all.length
            else
              scope.to_a.each do |record|
                record.run_callbacks :destroy
              end

              arel = scope.arel

              stmt = Arel::DeleteManager.new arel.engine
              stmt.from scope.klass.arel_table
              stmt.wheres = arel.constraints

              count = scope.klass.connection.delete(stmt, 'SQL', scope.bind_values)
            end
          when :nullify
            count = scope.update_all(source_reflection.foreign_key => nil)
          else
            count = scope.delete_all
          end

          delete_through_records(records)

          if source_reflection.options[:counter_cache] && method != :destroy
            counter = source_reflection.counter_cache_column
            klass.decrement_counter counter, records.map(&:id)
          end

          if through_reflection.macro == :has_many && update_through_counter?(method)
            update_counter(-count, through_reflection)
          end

          update_counter(-count)
        end