# File lib/ohm.rb, line 1473
    def self.filters(dict)
      unless dict.kind_of?(Hash)
        raise ArgumentError,
          "You need to supply a hash with filters. " +
          "If you want to find by ID, use #{self}[id] instead."
      end

      dict.map { |k, v| to_indices(k, v) }.flatten
    end