code: func (s *Store) TxFindAggregate(tx *bolt.Tx, dataType interface{}, query *Query, groupBy ...string) ([]*AggregateResult, error) {
  	return aggregateQuery(tx, dataType, query, groupBy...)
  }
docs: // TxFindAggregate is the same as FindAggregate, but you specify your own transaction
  // groupBy is optional