Would you add a StrategizedProperty is_eager() method?
class StrategizedProperty(MapperProperty):
...
@property
def is_eager(self):
return self.lazy in (False, 'joined', 'subquery')
...
Actually, I guess it would belong as part of class
RelationshipProperty instead.
Kent
On Mar 5, 11:54 am, Michael Bayer <[email protected]> wrote:
> On Mar 5, 2011, at 11:44 AM, Kent wrote:
>
> > Yep, works excellent (the "Why??" I asking about why is it wrong to
> > invoke "prop.do_init()" instead of StrategizedProperty.do_init(prop))
>
> oh. because you don't want to rerun all the initialization crap in
> RelationshipProperty which I'm not even sure supports being run on itself
> twice. So just StrategizedProperty's part is run.
>
> this of course could be a public API function, but then it falls into the
> why-is-1%-of-SQLA-configuration-mutable-and-not-the-other-99% issue we had
> like when you were mutating table.c that time.
>
>
>
> > On Mar 5, 11:31 am, Michael Bayer <[email protected]> wrote:
> >> 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 <[email protected]> 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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