Sum felds with with sqlalchemy and marshmallow

Question

I'm using the python's framework pyramid, sqlalchemy for the data and marshmallow to serialize. I'm want to send a sum of value to the client

I have Challenge and player whom use this challenge, each actions of the player is an event and each events has a duration.

For each challenge, i want to send the sum's duration for each player and also send this value only for one player. I try to use hybrid attribute or pre_dump function but i didn't succeeded

1. First method : with hybrid attribute

   __tablename__ = "Challenge"
   id = Column(Integer, primary_key=True)
   name = Column(String(255), unique=True, nullable=False)
   description = Column(TEXT(length=65535))
   map_url = Column(String(255))
   end_date = Column(DateTime(timezone=False))
   alone_only = Column(Integer)
   level = Column(String(255))
   scalling = Column(Integer)
   draft = Column(Boolean, server_default=text("0"))
   admin_id = Column(Integer, ForeignKey("User.id"))
   admin = relationship("User", backref="challenge_manager")
   event_sum_user = relationship("Events")```
   
   @hybrid_property
   def event_sum(self):
        return sum(Events.duration for Events in self.event_sum_user)
   
   

But i have sum for all user, not by user or for one user

2. Second method :with pre_dump method

   id = fields.Int()
   name = fields.Str()
   description = fields.Str()
   end_date = fields.DateTime()
   alone_only = fields.Int()
   level = fields.Str()
   scalling = fields.Int()
   draft = fields.Bool()
   admin = fields.Nested(UserSchema)
   admin_id = fields.Int(load_only=True)
   event_sum = fields.Int(dump_only=True)  
   
   @pre_dump
   def get_eventsum(self,data, **kwargs):
       data["event_sum"] = DBSession.query(func.sum(Events.duration)).filter(Events.challenge_id==data["id"]).filter(Events.user_id==1).first()
       return data```
   

With this method, i've have an error TypeError: 'Challenge' object is not subscriptable'

The purpose of this is to send with each challenge the total duration realise by a user or for each user on the challenge : id_user and total duration.

Thanks for your help

Marilyn