handle empty influx response better

aid/provide/influx_trains.py

@@ -17,7 +17,7 @@
 class InfluxTrainProvider(BaseProvider):
     # TODO better name, changing from postgres to influx kind of on the fly now
 
-    def get_trains(self, start: datetime, end: datetime) -> pd.DataFrame:
+    def get_trains(self, start: datetime, end: datetime) -> pd.DataFrame | None:
         """
         Get train data from InfluxDB as a data frame.
 
@@ -45,6 +45,9 @@ def get_trains(self, start: datetime, end: datetime) -> pd.DataFrame:
         query_api = self._influx_client.query_api()
         df = query_api.query_data_frame(query=query, use_extension_dtypes=True)
 
+        if df.empty:
+            return None
+
         time_query_done = perf_counter()
         logger.debug("Influx query time", duration=time_query_done - time_start)
 
@@ -67,6 +70,8 @@ def get_trains_as_records(self, start: datetime, end: datetime) -> list[TrainRec
         Get train data from InfluxDB as a list of pydantic records.
         """
         gdf = self.get_trains(start, end)
+        if gdf is None:
+            return []
 
         output = [
             TrainRecord(

aid/provide/routers/trains.py

@@ -4,7 +4,7 @@
 from typing import TypeAlias
 
 import pandas as pd
-from fastapi import APIRouter, Security
+from fastapi import APIRouter, Security, HTTPException
 from pydantic import BaseModel
 
 from aid.constants import DEFAULT_TIMEZONE
@@ -79,6 +79,9 @@ def get_pivoted_data(start: datetime | None = None, end: datetime | None = None)
     end = end or datetime.now(DEFAULT_TIMEZONE)
     start = start or end - timedelta(seconds=10)
     df = InfluxTrainProvider().get_trains(start, end)
+    if df is None:
+        raise HTTPException(status_code=204)  # no content
+
     df = df.rename(
         columns={
             "_time": "timestamp",