On Mar 5, 2011, at 11:18 AM, Kent wrote:
> Thank you!
>
> I don't disagree: I've been brainstorming how to work it out upfront,
> but I think I'd need your topological sort to put the mappers in the
> correct dependency order and since it is legacy support, I'm ok with
> the non public API and potential consequences.
>
> I had tried prop.do_init() in place of
> StrategizedProperty.do_init(prop), but it failed.
>
> Why??? (would invoke RelationshipProperty.do_init(), but I would have
> guess that was the correct method instead of StrategizedProperty's)
here it is:
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class Parent(Base):
__tablename__ = 'parent'
id = Column(Integer, primary_key=True)
children = relationship("Child", lazy='joined', backref=backref('parent',
lazy='joined'))
class Child(Base):
__tablename__ = 'child'
id = Column(Integer, primary_key=True)
parent_id = Column(Integer, ForeignKey('parent.id'))
compile_mappers()
from sqlalchemy.orm import strategies, interfaces
for prop in (Parent.children.property, Child.parent.property):
prop.strategy_class = strategies.factory('subquery')
interfaces.StrategizedProperty.do_init(prop)
e = create_engine('sqlite://', echo=True)
Base.metadata.create_all(e)
s = Session(e)
s.add(Parent(children=[Child(), Child()]))
s.commit()
print "----------------------"
s.query(Parent).all()
s.close()
print "----------------------"
s.query(Child).all()
>
>
>
>
> On Mar 5, 11:04 am, Michael Bayer <mike...@zzzcomputing.com> wrote:
>> On Mar 5, 2011, at 10:37 AM, Kent wrote:
>>
>>
>>
>>> Oracle 8 strikes again. But our client's current legacy application
>>> requires it (until we can get them off the app).
>>
>>> Anyway, when Oracle 8 is detected, I wish to convert certain mapper
>>> properties' lazy attribute from False => 'subquery' because oracle 8
>>> isn't smart enough to run the query anywhere near efficiently (but 9i
>>> is).
>>
>>> So, after all the mappers are compiled (I need backrefs also), I'm
>>> looping through the _mapper_registry and detecting which properties
>>> need to be converted if the oracle is 8i.
>>
>>> Unfortunately for me:
>>> prop.lazy = 'subquery'
>>> prop.strategy_class = strategies.factory('subquery')
>>
>>> isn't enough because the prop.strategy was already initialized I
>>> surmise.
>>
>>> Because of potential circular references and complications with
>>> backrefs and future mapped classes not being mapped to a table until
>>> after mapper() is invoked for the class, I do not think I can figure
>>> out whether lazy should be False vs. 'subquery' during the mapper()
>>> invocation...(at least trivially), so I am waiting until after all
>>> mappers are compiled.
>>
>>> Can you think of any solutions for me? Any way to change a properties
>>> lazy attribute after it's been instantiated? Any way to clone the
>>> property and replace it with a new one with a difference lazy
>>> attribute?
>>
>> If it were me I'd still try to solve the problem of deciding which
>> relationships/backrefs need the setting up front. You can limit it to
>> those who are setting up lazy="joined" I assume, and i'd consider getting
>> ugly too with some hardcoding, since this is for legacy support anyway.
>>
>> Otherwise the internal API magic you need would be:
>>
>> from sqlalchemy.orm.interfaces import StrategizedProperty
>>
>> prop.strategy_class = strategies.factory('subquery')
>> StrategizedProperty.do_init(prop)
>>
>> which would reset the "self.strategy" attribute and the collection of
>> alternate strategies.
>
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