merge

# File activerecord/lib/active_record/relation/merger.rb, line 65
      def merge
        normal_values.each do |name|
          value = values[name]
          # The unless clause is here mostly for performance reasons (since the `send` call might be moderately
          # expensive), most of the time the value is going to be `nil` or `.blank?`, the only catch is that
          # `false.blank?` returns `true`, so there needs to be an extra check so that explicit `false` values
          # don't fall through the cracks.
          unless value.nil? || (value.blank? && false != value)
            if name == :select
              relation._select!(*value)
            else
              relation.send("#{name}!", *value)
            end
          end
        end

        merge_multi_values
        merge_single_values
        merge_clauses
        merge_preloads
        merge_joins
        merge_outer_joins

        relation
      end