On Jun 26, 2010, at 7:28 AM, Michel Albert wrote:
>
> Thanks for the answer. From the docs, this seems to be what I am
> looking for. But it sill isn't quite giving me what I want. For
> reference, here's the mapper:
>
> mapper( Item, item, properties={
> 'owner': relation( Contact, backref='owned_items',
> primaryjoin=item.c.owner_id==contact.c.contact_id,
> passive_deletes="all"),
> 'holder': relation( Contact, backref='held_items',
> primaryjoin=item.c.holder_id==contact.c.contact_id,
> passive_deletes=True ),
> } )
>
> In the case of my application I want owner to be a "compulsory"
> relation, and "holder" an optional one. So, if an "owner" gets
> deleted, I want all items to be removed as well. For that I have the
> "ON DELETE CASCADE" rule in the DB.
SQLA wants to know about that so you'd also include cascade="all,
delete-orphan" on the relationship. passive_deletes then gets set just to
"True", so that it won't load unloaded rows unnecessarily.
> On the other hand however, as
> holders are optional they should simply be set to NULL if the related
> contact disappears.
and on that one you leave the usual UPDATE behavior in place.
> This is why I used the two different values for
> "passive_deletes". The way I understand the docs, having
> passive_deletes set to True or "all" let's the DB handle referential
> integrity.
But SQLA still needs to know what it should do with objects that are present in
the session. "passive_deletes" doesn't mean "won't touch it". It means, "won't
load unloaded rows to make sure they are also deleted". I just re-read the
mapping and API docs for it and to me they appear to be pretty clear on that
point.
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