I used before_delete and after_commit and it works like a charm. Thanks
again!
I have another problem related to this setup. I have a property defined on
the Image model:
@property
def filename(self):
return '{basename}.{extension}'.format(basename=self.basename, extension
=self.extension)
When I make this query:
image = db.session.query(Image).get(100)
image.filename
I get the filename property istantly but when I do it like this:
node = db.session.query(Node).get(100)
node.filename
Another query has to be issued which is not what I want. Do you know any
possible solution to that problem Michael?
W dniu wtorek, 25 sierpnia 2015 17:16:16 UTC+2 użytkownik Michael Bayer
napisał:
>
>
>
> On 8/25/15 10:05 AM, Jakub Bąk wrote:
>
> I just came across a solution to this problem. Adding 'with_polymorphic':
> '*' to __mapper_args__ on the Node model was enough.
>
> class Node(db.Model):
> id = db.Column(db.Integer, primary_key=True)
> type = db.Column(db.String(20))
> name = db.Column(db.String(30), nullable=False)
> date_added = db.Column(db.DateTime, default=datetime.now())
> parent_id = db.Column(db.Integer, db.ForeignKey('node.id'), nullable=
> True)
> path = db.Column(db.String(200), default='')
> __mapper_args__ = {'polymorphic_on': type,
> 'with_polymorphic': '*' }
>
>
> OK, yeah that's a funny problem you have. The with_polymorphic in all
> cases is going to lead to heavier queries, because there's the join but
> also if you already have joins between Node classes, you'll start to see
> some very long queries with lots of joins / sub-joins.
>
> A more portable solution would be to also implement before_delete(), where
> you either ensure that the Image columns are loaded, or you add the files
> to be deleted to some kind of collection; then you'd actually delete the
> files using a safer event like after_commit(), so that way if your
> transaction fails, the files are preserved.
>
>
>
>
>
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