Still getting the hang of SQLAlchemy terminology.
I didn't mean a simple deferred() column, but a deferred column_property()
which defines a scalar select(). Like in the example here
http://www.sqlalchemy.org/docs/orm/mapper_config.html#sql-expressions-as-mapped-attributes
.
My goal is to, instead of including a correlated subquery in the SELECT. The
column_property looks like
Customer.num_orders = orm.column_property(
select([func.count(Order.id)])\
.where(Order.customer_id == Customer.id)\
.correlate(Customer.__table__),
deferred=True
)
I'd rather do a separate query to load num_orders, rather than getting it
lazily or by using undefer(). It almost feels like I might want to define
num_orders as a relationship somehow? I dunno if what I would like to do
maps cleanly to a SQLAlchemy pattern.
On Wed, Sep 7, 2011 at 7:51 AM, Michael Bayer <mike...@zzzcomputing.com>wrote:
> For a deferred() itself, we don't have an option that does this. Though
> this is an unusual request. If you definitely want the deferreds to load,
> what's the issue having them render inline into the original query ? The
> advantage to "subqueryload" is primarily in that it loads multiple rows per
> parent object efficiently, without re-fetching the full parent row many
> times, or needing to use a less efficient OUTER JOIN. A deferred is
> always one row per parent - and no join is needed anyway.
>
>
>
>
> On Sep 6, 2011, at 6:49 PM, Sumeet Agarwal wrote:
>
> > I have a collection of deferred `ColumnProperty`s that I'd like to
> > start loading in subsequent queries. I know you can get this to happen
> > on the first access of a `ColumnProperty` that is deferred, but I
> > wonder if there's any way to specify this in the query.
> >
> > For relationships, `joinedload[_all()]` has a counterpart
> > `subqueryload[_all()]`. Is there nothing similar we can do for
> > `ColumnProperty`?
> >
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