I ran into a not so unusual case today where I need a count of children
for each parent in a one to many relationship. I first thought of what
I would do with SQL. I would join the tables and use a COUNT aggregate.
Then I thought about how I might approach it with SQLAlchemy. There
is the select approach that is almost identical to the SQL approach and
then there is the ORM approach. I don't have many parent records, so I
don't mind selecting them all, but I certainly don't want to select all
of the child records.
parents = session.query(Parent).select()
counts = [len(parent.children) for parent in parents]
The problem with this is that len(parent.children) selects all of the
child records (I think). It would be nice if len(parent.children)
triggered a COUNT instead. Or maybe children could have a count method
so it would look like this:
parents = session.query(Parent).select()
counts = [parent.children.count() for parent in parents]
Does a simple and efficient ORM approach already exist? If not, what do
you think of these two approaches?
Randall
-------------------------------------------------------------------------
Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys -- and earn cash
http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV
_______________________________________________
Sqlalchemy-users mailing list
Sqlalchemy-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/sqlalchemy-users
