Hello,
On Jan 21, 2011, at 1:48 AM, Juliusz Gonera wrote:
> Is it considered bad practice to make DB queries in model's methods? Or is
> this the way to go?
Yes, it's a bad practice in general -- model should be persistence-agnostic.
And even if you're not planning to use the same models with different storage
options or outside of SQLAlchemy context, I still recommend you to separate
queries and data manipulation routines in separate class -- ModelManager,
ModelRepository, ...
The rules that I follow are:
* If function operates on entire table (insert something into table, query
from table or etc.) -- it should become a member or model's manager.
* If function is a part of behavior of model (in a sense of its domain)-- it
should become model's method.
So, I think it's worth to delegate such relationship management to model's
manager:
class MainModelManager(object):
def add_some_related_object(self, main_obj, param1, param2):
# query something
related = SomeRelatedObject()
main_obj.some_related_objects.append(related)
If you think, that this method would require also some participation of main
model's inner state, you can replace
`main_obj.some_related_objects.append(related)` with special method of
MainModel:
class MainModel(object):
def add_some_related_object(self, related):
# some business logic, which is not require database access
main_obj.some_related_objects.append(related)
class MainModelManager(object):
def add_some_related_object(self, main_obj, param1, param2):
# query something
related = SomeRelatedObject()
main_obj.add_some_related_objects(related)
This way you can separate business logic from persistence.
It also helps to provide better testability of you code, cause you can test
domain logic inside `MainModel.add_some_related_object` without requiring
existence of test SQL database.
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