On 06/30/2010 03:32 AM, Paul Johnston wrote:
> Hi,
>
> I hope everyone's well here. It's been some time since I posted. Great
> to see it up to 0.6, and even more progress on MS-SQL (although I'm
> now unlikely to be using that).
>
> As always, I'm using SQLAlchemy as part of a web app. I have a set of
> checkboxes, which I'm saving into an M:M relation. The app receives a
> list of IDs from the client. To save these to the M:M, I need them as
> database objects. So I'm doing (roughly):
>
> myobj.relation = [OtherTable.get(i) for i in ids]
>
> The problem with this is it's causing a database query for each id.
> What I'd really like to do is somehow create a "placeholder" object
> with just the id, that doesn't cost a database query to create. After
> that, I'll trust flush() to do its magic as efficiently as possible.
>
> Paul
>
>
Here's an ugly way to do it, which injects a persistent OtherTable
instance into the session without verifying it exists in the database.
from sqlalchemy.orm import identity_key_from_primary_key
from sqlalchemy.orm.attributes import instance_state
def inject_persistent_instance(session, cls, primary_key):
temp = cls()
state = instance_state(temp)
state.key = identity_key_from_primary_key(primary_key)
return session.merge(temp)
myobj.relation = [inject_persistent_instance(session, OtherTable, i) for i in
ids]
# You risk flush errors if the OtherTable rows did not exist in the database.
session.flush()
-Conor
--
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To post to this group, send email to sqlalch...@googlegroups.com.
To unsubscribe from this group, send email to
sqlalchemy+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en.
