I often find myself wanting to do something like this:
for address in user.addresses:
if address.street == "123 Elm Street":
# there's an address from this street, so do something
break
else:
# do nothing; no addresses from that street
That could also be accomplished with SQL:
address = Session.query(Address).filter(Address.user ==
user).filter(Address.street == "123 Elm Street")
Or, in certain cases, I need a join:
try:
user = Session.query(User).join(Address).filter(Address.street ==
"123 Elm Street").one()
# There was someone at that address, so do something
except:
# None Found; don't do anything
pass
So there are usually two ways to approach these problems: ORM-mappings
or SQL queries. If I use the ORM-mapping approach, SQLAlchemy
generally only needs to eagerload the collection once -- so if I have
multiple functions that operate on mapped data, I only incur the
database load once. If I do it with SQL querys, it queries the
database multiple times (once for each query).
What's the best approach for this type of thing? Is it best practice
(performance-wise) to prefer SQL queries over looping through ORM-
mapped properties, even if SQLAlchemy needs to issue a few more SQL
queries instead?
Obviously I'd need to do performance testing for specific cases. I've
preferred the looping-on-ORM-relations approach because it's clearer
in my mind, but if it'd be much more performant to have SQLAlchemy
query when I need the data via SQL querying, I'll reevaluate.
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