On 9/15/15 10:09 AM, Jakub Bąk wrote:
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
deffilename(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?
that is again the way the joined-table inheritance works; by default it
only queries the base table. Per query you'd do it like this:
session.query(Node).with_polymorphic(Image).get(100)
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.
|
classNode(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
<http://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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