On Mon, 17 Nov 2008, Faheem Mitha wrote:
> Hi,
>
> I've written a session transcript to init db tables and add objects
> (well, rows) to the tables. The issue I'm currently facing is how to
> make the "creating and populating the tables" section of the script a
> no-op when the objects exist. If the tables already exist sqlalchemy
> does nothing, which is fine. However, this script currently does try to
> add the objects that are already there, and so throws an exception. I
> suppose the thing to do would be to check for each object whether it
> already exists in the db, and do nothing if so. What would be the
> simplest/cleanest way to do so? I've been fiddling with this for a while
> without finding an obviously good solution. Is it possible to check
> whether an "object" is already in a specific table?
[following up to my own message]
The following approach works, but is kinda kludgy. In particular, I'd like
to genericise it. The main obstacle in doing so is finding a generic
expression for the primary key. There is always a primary key, and by
definition it is unique, right? So, I think it makes sense to use that for
comparison, but the actual name of the primary key can differ and is can
also be composite. So, is there a way to access it in a generic way?
Alternatively, is there a better approach to this?
Thanks, Faheem.
def add_patient_obj(session, patient_obj):
""" Check if object primary key exists in db. If so,exit, else add."""
pid = patient_obj.id
if session.query(Patient).filter_by(id=pid).count() > 0:
print "Patient object with id %s is already in db."%pid
exit
else:
session.save(patient_obj)
session.commit()
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