[sqlalchemy] Re: disable polymorphic load
thats a bug which was fixed post 0.4.7p1. Its in trunk and is for 0.4.8. Great! And back to the mapper properties. As I found it always do a polymorphic_fetch=select-like query when dealing with mapper properties referencing a polymorphic base. This is not very efficient. I would prefer an union fetch. I realized that it is similar to query().get(). Example follows: session.query(Base).with_polymorphic(*).filter(Base.id==3).first().x results in 1 joined select: SELECT base.id AS base_id, base.id_parent AS base_id_parent, base.kind AS base_kind, derived.id AS derived_id, derived.x AS derived_x, derived.id_other AS derived_id_other FROM base LEFT OUTER JOIN derived ON derived.id = base.id WHERE base.id = ? ORDER BY base.oid LIMIT 1 OFFSET 0 but session.query(Base).with_polymorphic(*).get(3).x results in 2 selects: SELECT base.id AS base_id, base.id_parent AS base_id_parent, base.kind AS base_kind FROM base WHERE base.id = ? SELECT derived.x AS derived_x, derived.id_other AS derived_id_other FROM base JOIN derived ON derived.id = base.id WHERE base.id = ? Both queries gives the same object but the get() generates 2 selects (like the mapper property fetch). Why? --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: disable polymorphic load
On Aug 26, 2008, at 8:24 AM, ml wrote: thats a bug which was fixed post 0.4.7p1. Its in trunk and is for 0.4.8. Great! And back to the mapper properties. As I found it always do a polymorphic_fetch=select-like query when dealing with mapper properties referencing a polymorphic base. This is not very efficient. I would prefer an union fetch. I realized that it is similar to query().get(). Example follows: session.query(Base).with_polymorphic(*).filter(Base.id==3).first().x results in 1 joined select: SELECT base.id AS base_id, base.id_parent AS base_id_parent, base.kind AS base_kind, derived.id AS derived_id, derived.x AS derived_x, derived.id_other AS derived_id_other FROM base LEFT OUTER JOIN derived ON derived.id = base.id WHERE base.id = ? ORDER BY base.oid LIMIT 1 OFFSET 0 but session.query(Base).with_polymorphic(*).get(3).x results in 2 selects: SELECT base.id AS base_id, base.id_parent AS base_id_parent, base.kind AS base_kind FROM base WHERE base.id = ? SELECT derived.x AS derived_x, derived.id_other AS derived_id_other FROM base JOIN derived ON derived.id = base.id WHERE base.id = ? Both queries gives the same object but the get() generates 2 selects (like the mapper property fetch). Why? yup..this is one of many things inheritance related that works properly in 0.5 --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: disable polymorphic load
One more thing :-) Now I have polymorphic_fetch=deferred and in some needed cases I call query.with_polymorphic(*). All works perfectly. But can I setup something like with_polymorphic(*) on a mapper property? Because now all relations to Base are polymorphic-deferred and it does me some troubles. Michael Bayer napsal(a): oh, that. OK, in the 0.4 series you'd want to set polymorphic_fetch='deferred' on your mapper. Just leave it that way, as the non-deferred behavior has been removed from 0.5 anyway (its deferred in all cases). The second table will be fetched as needed. if you're depending heavily on inheritance I strongly recommend looking at 0.5, this is one area where a significant amount of work has been done. On Aug 25, 2008, at 11:24 AM, ml wrote: This is not working: Setup: base = Table(base, metadata, Column(id, Integer, primary_key=True), Column(kind, Integer), ) derived = Table(derived, metadata, Column(id, Integer, ForeignKey(base.id), primary_key=True) ) class Base(object): pass class Derived(Base): pass mapper(Base, base, polymorphic_on=base.c.kind, polymorphic_identity=0, ) mapper(Derived, derived, inherits=Base, polymorphic_identity=1, ) and this call: session.query(Base).with_polymorphic(Base).first() will still result in 2 SELECTs and the returned object is Derived (tables are filled only with Derived objects) SELECT base.id AS base_id, base.kind AS base_kind FROM base ORDER BY base.id LIMIT 1 OFFSET 0 SELECT derived.id AS derived_id FROM derived WHERE %(param_1)s = derived.id __main__.Derived object at 0xce1b10 SQLAlchemy version 0.4.7p1 I need only 1 SELECT and Base object returned. Michael Bayer napsal(a): call with_polymorphic passing in only the base class: query.with_polymorphic(BaseClass).filter() On Aug 25, 2008, at 10:35 AM, ml wrote: Hi! How can I disable a polymorphic load for a single query? I found a hint in http://markmail.org/message/2kwbm377j3pdvvqb but I can't find more. Thanks for any advice. David --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: disable polymorphic load
On Aug 25, 2008, at 1:05 PM, ml wrote: One more thing :-) Now I have polymorphic_fetch=deferred and in some needed cases I call query.with_polymorphic(*). All works perfectly. But can I setup something like with_polymorphic(*) on a mapper property? Because now all relations to Base are polymorphic-deferred and it does me some troubles. not really. What kind of problems ? --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: disable polymorphic load
I created a stripped version of my application's model and I found the
problem. The problem is not in the polymorphism but int the inheritance
condition. I have cycles in my model so I had to use the
inherit_condition. I found that it is a big difference how I choose the
expression sides
inherit_condition=derived.c.id==base.c.id
or
inherit_condition=base.c.id==derived.c.id
But why? Is my inherit_condition incorrect at all?
The example code is attached.
Michael Bayer napsal(a):
On Aug 25, 2008, at 1:05 PM, ml wrote:
One more thing :-)
Now I have polymorphic_fetch=deferred and in some needed cases I
call
query.with_polymorphic(*). All works perfectly. But can I setup
something like with_polymorphic(*) on a mapper property? Because now
all relations to Base are polymorphic-deferred and it does me some
troubles.
not really. What kind of problems ?
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#!/usr/bin/python
# -*- coding: utf-8 -*-
from sqlalchemy import *
from sqlalchemy.orm import *
#engine = create_engine(postgres://localhost/test, echo=True)
engine = create_engine(sqlite://, echo=True)
metadata = MetaData()
base = Table(base, metadata,
Column(id, Integer, primary_key=True),
Column(id_parent, Integer, ForeignKey(base.id)),
Column(kind, Integer),
)
derived = Table(derived, metadata,
Column(id, Integer, ForeignKey(base.id), primary_key=True),
Column(x, Integer),
Column(id_other, Integer),
ForeignKeyConstraint([id_other], [base.id],
other_fg, use_alter=True),
)
class Base(object):
def __init__(self, id, parent):
self.id = id
self.parent = parent
class Derived(Base):
def __init__(self, id, parent):
Base.__init__(self, id, parent)
self.x = id
mapper(Base, base,
polymorphic_on=base.c.kind,
polymorphic_identity=0,
polymorphic_fetch=deferred,
properties = {
children: relation(Base, cascade=all,
backref=backref(parent, remote_side=[base.c.id])),
}
)
mapper(Derived, derived,
inherits=Base,
#inherit_condition=base.c.id==derived.c.id,
inherit_condition=derived.c.id==base.c.id,
polymorphic_identity=1,
properties = {
other: relation(Base, cascade=all, post_update=True,
primaryjoin=derived.c.id_other==base.c.id)
}
)
metadata.drop_all(engine)
metadata.create_all(engine)
Session = sessionmaker(bind=engine, autoflush=False, transactional=False)
session = Session()
#
# test data - chain 1-2-3
session.save(Derived(3, Derived(2, Derived(1, None
session.save(Derived(6, Derived(5, Derived(4, None
session.flush()
session.clear()
#
q = session.query(Base).with_polymorphic(*).get(3)
assert q.parent.parent.x == 1
q = session.query(Base).with_polymorphic(*).get(6)
assert q.parent.parent.x == 4, q.parent.parent.x
[sqlalchemy] Re: disable polymorphic load
On Aug 25, 2008, at 5:38 PM, ml wrote: I created a stripped version of my application's model and I found the problem. The problem is not in the polymorphism but int the inheritance condition. I have cycles in my model so I had to use the inherit_condition. I found that it is a big difference how I choose the expression sides inherit_condition=derived.c.id==base.c.id or inherit_condition=base.c.id==derived.c.id But why? Is my inherit_condition incorrect at all? The example code is attached. thats a bug which was fixed post 0.4.7p1. Its in trunk and is for 0.4.8. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: disable polymorphic load
sorry not trunk, the head of the 0.4 branch. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
