code: func (t *TxStructure) HGetInt64(key []byte, field []byte) (int64, error) {
  	value, err := t.HGet(key, field)
  	if err != nil || value == nil {
  		return 0, errors.Trace(err)
  	}
  
  	var n int64
  	n, err = strconv.ParseInt(string(value), 10, 64)
  	return n, errors.Trace(err)
  }
docs: // HGetInt64 gets int64 value of a hash field.