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
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