UPDATE

weather/water_need_prediction.py

@@ -2,6 +2,7 @@ from __future__ import annotations
 
 from typing import Any
 
+from farm_data.services import clone_snapshot_as_runtime_plant, get_primary_plant_snapshot
 from irrigation.evapotranspiration import calculate_forecast_water_needs, resolve_crop_profile
 
 from farm_data.models import SensorData
@@ -12,8 +13,7 @@ from .services import get_forecast_for_location
 
 def build_water_need_prediction_payload(*, sensor: Any, forecasts: list[Any]) -> dict[str, Any]:
     location = getattr(sensor, "center_location", None)
-    plants = list(sensor.plants.all()) if hasattr(sensor, "plants") else []
-    plant = plants[0] if plants else None
+    plant = clone_snapshot_as_runtime_plant(get_primary_plant_snapshot(sensor))
     irrigation_method = getattr(sensor, "irrigation_method", None)
 
     if not forecasts or location is None:
@@ -53,7 +53,7 @@ class WaterNeedPredictionService:
     def get_water_need_prediction(self, *, farm_uuid: str) -> dict[str, Any]:
         sensor = (
             SensorData.objects.select_related("center_location", "irrigation_method")
-            .prefetch_related("plants")
+            .prefetch_related("plant_assignments__plant")
             .filter(farm_uuid=farm_uuid)
             .first()
         )