gistfile1.rb

  def method_missing(name, *terms)
    if match = name.to_s.match(/search_by_(?<columns>[_a-zA-Z]\w*)/)
      string_columns = self.columns.select {|column| column.type == :string }.map(&:name)
      columns = match[:columns].split('_and_')
      super unless columns.all? {|column| string_columns.include?(column) }
      query = columns.inject({}) do |query, column|
        query.merge column => terms.shift
      end
      search(query)
    end
  end