On 5/30/2010 7:36 AM, nospam wrote:
Thanks Lance. Would this lazily load the annotations for each item?
I'm trying to avoid "# of item" trips to the db, and also avoid
loading all the annotations.for each item. I'm thinking I can do w/
some joins, and subquery()'s...
This would load the annotations lazily in that they would not be fetched
along with each item initially, but they would be as soon as you
reference item.annotations in code. This behavior is default, but you
can explicitly state it in your mapper like so:
orm.mapper(
Item, items,
properties = dict(
annotations = orm.relation(Annotation,
order_by=[annotations.c.creation_datetime.desc()], lazy='select'),
),
)
More on the relationship mapping is at
http://www.sqlalchemy.org/docs/reference/orm/mapping.html#sqlalchemy.orm.relation
.
However, it sounds like you need to know about the annotations within
your item loop anyway, so I'm not clear what you look to save yourself
in terms of "# of item trips to the db"? Just a suggestion, but I think
improving the speed of things might be easier later, and possibly even
unnecessary. Or it could be that I'm just not understanding what you're
after here. ;)
Also remember you can pass echo=True when creating your engine, e.g.:
my_engine = sa.create_engine('sqlite:///', echo=True)
Then you'll see exactly what SQL is being issued to your database and in
what order, etc.
(http://www.sqlalchemy.org/docs/reference/sqlalchemy/connections.html#sqlalchemy.create_engine)
Lance
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