use generated column instead

Author: peterdudfield

nowcasting_datamodel/models/forecast.py

@@ -16,6 +16,7 @@
     JSON,
     Boolean,
     Column,
+    Computed,
     DateTime,
     Float,
     ForeignKey,
@@ -105,26 +106,6 @@ def create_partition(
         return super().__new__(cls, clsname, bases, attrs)
 
 
-def default_horizon_minutes(context):
-    """Make a default horizon minutes for the ForecastValueSQLMixin"""
-    columns = context.get_current_parameters()
-    target_time = columns["target_time"]
-    created_utc = columns["created_utc"]
-
-    if created_utc is None:
-        created_utc = datetime.now(tz=timezone.utc)
-
-    if isinstance(target_time, str):
-        target_time = datetime.fromisoformat(target_time)
-
-    # make sure they both have tz, or not
-    if target_time.tzinfo is None:
-        created_utc = created_utc.replace(tzinfo=None)
-
-    delta = (target_time - created_utc).total_seconds() / 60.0  # convert to minutes
-    return delta
-
-
 class ForecastValueSQLMixin(CreatedMixin):
     """One Forecast of generation at one timestamp
 
@@ -142,14 +123,11 @@ class ForecastValueSQLMixin(CreatedMixin):
     # we want to store the forecast horizon.
     # This is the difference between target_time and created_utc.
     # By storing the value queries should be faster when looking for an N hour forecast.
-    # I tried to use
-    # server_default = "CAST(EXTRACT(EPOCH FROM (target_time - created_utc))/60 as INT)"
-    # but this does not work.
     horizon_minutes = Column(
         Integer,
-        nullable=True,
+        Computed("CAST(EXTRACT(EPOCH FROM target_time - created_utc)/60 as INT)"),
+        nullable=False,
         index=True,
-        default=default_horizon_minutes,
     )
 
     @declared_attr

nowcasting_datamodel/save/update.py

@@ -291,7 +291,8 @@ def change_forecast_value_to_forecast_last_7_days(
 
     forecast_new = ForecastValueSevenDaysSQL()
     for key in ForecastValueSQL.__table__.columns.keys():
-        if hasattr(forecast, key):
+        # Dont copy horizon minutes column as this is a generated column
+        if hasattr(forecast, key) and key != "horizon_minutes":
             setattr(forecast_new, key, getattr(forecast, key))
 
     return forecast_new