def execute(self, recommendation_id, user_id) -> Activity:
if recommendation_id is None:
raise BadArgException()
# TEST IF RECOMMENDATION ALREADY IN ACTIVITY FOR THE USER
existing_activity = Activity.query. \
filter_by(user_id=user_id). \
filter_by(recommendation_id=recommendation_id).first()
if existing_activity:
raise AlreadyStartedException
activity = Activity()
activity.set_recommendation(recommendation_id)
activity.set_user(user_id)
BaseObject.check_and_save(activity)
return activity
