If there is no native way:
h_to_sym = ->(row){ row.keys.each_with_object({}) { |k, o|
o[k.to_sym] = row[k].is_a?(Hash) ? h_to_sym.(row[k]) : row[k] }
}
p res.map.with_object([]) { |row, h| h << h_to_sym.(row) }
This also supports joined models.