fix(cli/db): remove obsolete db subcommand

pkg/storage/storage.go

@@ -31,6 +31,13 @@ func Compression(measuredValues []*types.MeasuredValue) []*types.MeasuredValue {
 	now := format.FormatedTime()
 
 	for _, measuredValue := range measuredValues {
+
+		// If the sensor id does not exist in the map, a new map is initialized,
+		// which can assume measured value types as the key. Behind this key there
+		// is a pointer which refers to a measured value in the memory. This new map
+		// is added to the map "lastMeasuredValuesBySensors" under the sensor ID.
+		// This makes it possible to store one measured value per measured value
+		// type per sensor.
 		if _, ok := lastMeasuredValuesBySensors[measuredValue.SensorID]; !ok {
 			lastMeasuredValuesBySensors[measuredValue.SensorID] = make(map[types.MeasuredValueType]*types.MeasuredValue, 0)
 		}
@@ -93,21 +100,27 @@ func Round(measuredValues []*types.MeasuredValue, round float64) {
 	}
 }
 
-// Write measured values to the given storage endpoint url. The scheme must be
-// matched to a provider, if the scheme is not implemented, the function
-// returns an error
+// Write measured values to the given storage endpoint url. If the storage
+// provider defined to a file, the data will be overwritten. If a database
+// provider is used, the data is simply added without deleting the existing
+// data. The scheme must be matched to a storage provider, if the scheme is not
+// implemented, the function returns an error
 func Write(ctx context.Context, measuredValues []*types.MeasuredValue, storageEndpoint *url.URL) error {
 	switch storageEndpoint.Scheme {
 	case "file":
 		measuredValueLogfile := logfile.New(storageEndpoint.Path)
-		return measuredValueLogfile.Write(measuredValues)
+		storedMeasuredValues, err := measuredValueLogfile.Read()
+		if err != nil {
+			return err
+		}
+		storedMeasuredValues = append(storedMeasuredValues, measuredValues...)
+		return measuredValueLogfile.Write(storedMeasuredValues)
 	case "postgres":
 		database, err := db.New(storageEndpoint)
 		if err != nil {
 			return err
 		}
 		defer database.Close()
-
 		if err := database.InsertMeasuredValues(ctx, measuredValues); err != nil {
 			return err
 		}