Hi,
I'm trying to get aggregation functions to work as column_properties,
but I'm having a hard time figuring it out. The example below doesnt
work.. maybe someone can help?
ratings = Table('ratings', metadata,
Column('rating_key', Integer, primary_key=True),
Column('user_id', Integer, primary_key=True),
Column('rating', SmallInteger, default=0)
)
class Rating(object): pass
mapper(Rating,ratings,
properties = { 'count' : column_property(
select([func.count
(ratings.c.id)],ratings.c.id==ratings.c.id)),
'average': column_property(
select([func.avg
(ratings.c.rating)],ratings.c.id==ratings.c.id))
}
)
Test data:
sql.insert(ratings).execute([{'rating_key':1,'user_id':1,'rating':5},
{'rating_key':1,'user_id':2,'rating':4},
{'rating_key': 2,'user_id':1,'rating':1},
{'rating_key':3,'user_id':1,'rating':1},
{'rating_key':3,'user_id':2,'rating':1},
{'rating_key':3,'user_id':3,'rating':4},])
r = s.query(Rating).filter_by(rating_key=1,user_id=1).first()
desired result:
r.rating_key = 1
r_user_id = 1
r.rating = 5
r.average = 4.5 #averate all users for rating_key 1
r.count = 2 #rating count (users) for rating_key 1
thanks Bj
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