the _clone() on query is a shallow copy, otherwise it would be a serious
performance hit for a query that takes several generative steps to build
up. So you'd have to assign query's _order_by to a copy of itself if you
want to modify it in place like that. you can probably use
visitors.cloned_traverse() on the element to copy it, then also copy the
list of elements as well (look at the source to query.order_by() to see
the idea).
empty wrote:
>
> I realize I'm doing something hacky, but I'm wondering if this is the
> expected behavior. The issue is that if I modify the modifier on a
> UnaryExpression, even if I clone the Query ahead of time it modifies
> other Query instances. See the following:
>
> import datetime
> from sqlalchemy.ext.declarative import declarative_base
> from sqlalchemy import *
> from sqlalchemy.sql import operators
> from sqlalchemy.orm import sessionmaker
>
> engine = create_engine('sqlite://')
> Session = sessionmaker(bind=engine, autoflush=True, autocommit=False)
> session = Session()
> Base = declarative_base(engine=engine)
>
> class Category(Base):
> __tablename__ = 'foo_category'
>
> id = Column('id', Integer, primary_key=True)
> name = Column('name', String(50))
> created_at = Column('created_at', DateTime, nullable=True,
> onupdate=datetime.datetime.now)
>
> def __repr__(self):
> return self.name
>
>
> Base.metadata.create_all()
>
> session.add_all([Category(name='zzeek'),
> Category(name='jek'),
> Category(name='empty')])
>
> # order ascending
> c1 = session.query(Category).order_by(asc(Category.name))
> assert [u'empty', u'jek', u'zzeek'] == [c.name for c in c1]
>
> # clone the query and verify still asc
> c2 = c1._clone()
> assert [u'empty', u'jek', u'zzeek'] == [c.name for c in c2]
>
> # reverse the order_by modifier on c1
> c1._order_by[0].modifier = operators.desc_op
> assert [u'zzeek', u'jek', u'empty'] == [c.name for c in c1]
>
> # here's the problem, c2 is now modified
> assert [u'zzeek', u'jek', u'empty'] == [c.name for c in c2]
>
>
> Michael Trier
> blog.michaeltrier.com
>
> >
>
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