Hello everyone,
I have a realy simple model for you to consider:
1 car has n wheels
car.wheels is a relation from cars to wheels
wheel.car is a backref to cars
1 car has n parts
car.parts is a relation from car to parts
I just wondered why my app was really getting slow, turned on SA debug
mode, and saw that
my_new_doorknob = model.Part("doorknob")
wheel.car.parts.append(my_new_door_knob)
is downloading the entire "parts" table WHERE parts.car == car.id
(that is around 20.000 entries) just so that it can append my new
doorknob to that relation.
Furthermore I noticed a similar behaviour when doing something like this:
amount_of_parts = len(car.parts)
Instead of sending a COUNT to the database, it populates the entire
car.parts relation (around 20.000 entries) just to get the count. Of
course I could avoid using relations, and just use my __init__
functions, or setting:
my_new_doorknob = model.Part("doorknob")
my_new_doorknob.car_id = car.id
DBSession.append(my_new_doorknob)
But then I could as well just write literal SQL if I cant use the "R"
part of ORM...
Has anyone observed similar behaviour or is this a "feature" and
intended to work like this?
Greetings, Tom
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