code: func (mc MongoClient) Readings() ([]contract.Reading, error) {
  	readings, err := mc.getReadings(nil)
  	if err != nil {
  		return []contract.Reading{}, err
  	}
  
  	mapped := make([]contract.Reading, 0)
  	for _, r := range readings {
  		mapped = append(mapped, r.ToContract())
  	}
  	return mapped, nil
  }
docs: // Return a list of readings sorted by reading id