Hello,
I'm battling with Django in order to try avoiding object persistence when
initialising foreign key model attributes. The app I'm using Django for
implements a facade for an already existing database. It's main purpose is
to be used as a (read-only) ReST server returning objects built by
aggregating attributes from the already existing database. The Django app
itself has model classes (and associations) like any other Django app.
Renderers and Serializers based on those supplied by the rest_framework
modules have been written and tested. We started by configuring the Django
app to use a SQLite file, as we're don't really care about object
persistence. However, when building model instances (by
extracting/aggregating data from the original non-Django managed database),
we hit a severe perfomance bottleneck. Each time we initialize a model
attribute which is a collection of related instances, all these are
apparently persisted to the Django database.
For example, with a classical Order/Items association, we'd have :
01: orderattributes={...extract attributes from external database using
> SQL...}
> 02: order=Order(**orderattributes)
> 03: orderitems=[]
> 04: for item in ...items belonging to order...
> 05: itemattributes={...extract attributes from external database using
> SQL...}
> 06: item=Item(**itemattributes)
> 07: orderitems.append(item)
> 08: order.items_set=orderitems
When reaching line 8, it seems that every Item instance of the orderitems
collection is persisted in the Django database, which considerably slows
down the application.
I tried to use an in-memory SQLite database, but couldn't make it work, as
the syntax for declaring a shared in-memory database (file::memory:...) is
not handled correctly, yielding a file-based database instead.
Thus, I'd like to know if there is any means to by-pass the automatic
persistence mechanism when using collection attributes which are
foreign-key based.
Thanks for any pointers !
Marc'h
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