On 05.01.12 16:13, Michael Bayer wrote:
>
> On Jan 5, 2012, at 3:03 PM, Mariano Mara wrote:
>
> > Hi there! I have a master-detail entity. Since I do some post-processing
> > work
> > on the details before inserting the entity in the db, I added an
> > 'after_insert' event where I do the extra stuff.
> > One of the things I need is to make sure certain "details" have been
> > selected by the user and in case he didn't I add some default values on his
> > behalf, just like
> >
> > master.detail.append(DetailCls(score=100,
> > timestamp=datetime.datetime.now()))
>
> don't do any kind of manipulation of the flush plan, which includes
> collection alterations, inside of after_insert().
>
> The append() operation here is most cleanly implemented in the __init__
> method of your Master object. That way the model itself handles the shape it
> should be in.
>
> Another way to set up state is using the @validates hook to respond to an
> attribute set event:
>
> http://www.sqlalchemy.org/docs/orm/mapper_config.html?highlight=validates#simple-validators
>
> The other way is to use the before_flush event:
>
> http://www.sqlalchemy.org/docs/orm/events.html?highlight=before_flush#sqlalchemy.orm.events.SessionEvents.before_flush
>
Thanks a lot for the answer. As expected adding my logic in the __init__ was
the way to go.
I have a question though:
Let's say users can edit the detail instances of this master and in case I
detect that certain attribute is modified, I want invalidate the detail and
create
a new one. e.g.:
if get_history(inst_detail, "attr").has_changes():
inst_detail.active=False
new_detail = Detail(attr=new_attr, score=100)
master.append(new_detail)
My question is how I can skip the "attr" modification made in the old_instance?
I want to keep the active=False but I want to ignore the "attr" change. I
tried with several methods in Session (e.g. expunge) but the update occurs
nevertheless.
TIA,
Mariano
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