On 08/11/2016 09:53 AM, Douglas Russell wrote:
of_type was what I was searching for. Thanks.
Unfortunately, it did not yield the desired results when I extended the
hierarchy to 3 levels (C->C2 with a relation between B and C).
I've updated the Gist.
B+B2 is successfully queried, but C+C2 is not. This will then result in
lazily generated queries when accessing C2.
In fact, it's actually a little more confusing even than that. With that
query, it does (in the original query)
Query for all A+A2
Query for all B+B2 (from the subqueryload)
Then once I start to print the hierarchy out, lazy queries:
Query for all C
Query for each C2
I'm not sure how to document this (I guess just add another example) but
once you've done of_type(), that's now the type you're on and if you
chain from there, it has to be in terms of that new type. The
with_polymorphic() object you've made is that type (note the subclass
namespace that's on the object):
b_b2 = with_polymorphic(B, [B2], flat=True)
r = session.query(A2).options(
subqueryload(A2.bs.of_type(b_b2)).subqueryload(b_b2.B2.cs.of_type(
with_polymorphic(C, [C2], flat=True))
)
).all()
Cheers,
Douglas
On Wednesday, 10 August 2016 18:18:27 UTC-4, Douglas Russell wrote:
Hi,
I have two (well, more than two with more than two levels each, but
this is the simplest recreation of the problem) parallel
joined-table inheritance hierarchies
A -> A2
B -> B2
B.a is a relationship to A, backref in A.bs.
The problem arises when I want to query this whole structure back
with subqueries. The desired number of queries in this case would be
twoish, depending on how the polymorphic queries are done. At any
rate, the desire is to remove any lazy loading at all.
The problem lies in formulating a subqueryload which will do this.
My first thought was:
|
session.query(A2).options(subqueryload(A2.bs)).all()
|
The problem with this is that what I wanted was all the A2s and all
the B2s, but what I get is all the A2s, and all the Bs. When I
access a property of B2, it lazy loads that single record.
I think the best solution is something along the lines of using a
combination of subqueryload and joinedload (or maybe
with_polymorphic?) to say: Give me all the A2s with a subquery for
all the B2s linked to it. I can't figure out how to do this as the
arguments to subqueryload and joinedload are relationships which I
don't currently have.
Minimal Test
Case: https://gist.github.com/dpwrussell/508e8b33fe92434eafe001ee806f355a
<https://gist.github.com/dpwrussell/508e8b33fe92434eafe001ee806f355a>
Is there a clever way to handle this?
The only thing I've done which works is to add a relationship
between B to B2:
|
b = relationship('B', backref='b2')
|
Then I can do:
|
r =
session.query(A2).options(subqueryload(A2.bs).joinedload(B.b2)).all()
|
but it would be better if I didn't have to go and add these
relationships to the existing models as there are several levels,
repositories and (most hinderingly) jurisdictions in play in my real
project. It seems likely that there is a clever way as SQLAlchemy
does such a good job with the polymorphic queries usually.
Cheers,
Douglas
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