code: func (ec *EventClass) Query() (query.Query, error) {
  	if ec.query == nil {
  		var err error
  		ec.query, err = query.New(ec.Filter)
  		if err != nil {
  			return nil, err
  		}
  	}
  	return ec.query, nil
  }
docs: // Get a (memoised) Query from the EventClass Filter string