On Apr 24, 2012, at 3:36 PM, Michael Bayer <[email protected]> wrote:
>
> On Apr 24, 2012, at 1:16 PM, David Bowser wrote:
>
>> I have a mixin as follows designed to remove a bunch of copy paste
>> relationship code.
>>
>> class UserMixin(object):
>> @_declared_attr
>> def user_id(cls):
>> return
>> sa.Column('user_id',typ.Integer,sa.ForeignKey("tg_user.user_id",
>> ondelete="CASCADE"),nullable=False)
>>
>> @_declared_attr
>> def user(cls):
>> return orm.relationship("User",primaryjoin='%s.user_id ==
>> User.user_id'%cls.__name__)
>>
>> @_declared_attr
>> def user_profile(cls):
>> return orm.relationship('UserProfile',primaryjoin="%s.user_id ==
>> UserProfile.id"%cls.__name__,
>> foreign_keys=lambda:[metadata.tables['user_profiles'].c.id],
>> backref=cls.__tablename__ if cls.__tablename__ else
>> tablename(cls.__name__))
>>
>> when I use my mixin in say a class like this:
>>
>> class JournalEntry(UserMixin,DeclarativeBase):
>> __tablename__ = 'journal_entries'
>> #{ Columns
>> id = Column(Integer,primary_key=True)
>> is_private = Column(Boolean,default=False)
>> modified = Column(DateTime,onupdate=datetime.datetime.now)
>> text = Column(UnicodeText)
>> #}
>>
>> And then I:
>>
>>>>> from myProject.model import *
>>>>> profile = DBSession.query(UserProfile).get(1)
>>>>> profile.journal_entries
>>
>> I keep getting the error:
>>
>> /Users/Me/Documents/Work/Projects/myProject/myProject/lib/python2.7/site-packages/SQLAlchemy-0.7.6-py2.7-macosx-10.7-intel.egg/sqlalchemy/orm/strategies.py:508:
>> SAWarning: Multiple rows returned with uselist=False for lazily-loaded
>> attribute 'UserProfile.journal_entries'
>> < myProject.model.user_data.JournalEntry object at 0x10d8b26d0>
>>
>> I can't figure out why it's using uselist=False, and a joined lazy load. Any
>> help pointing me in the right direction would be great.
>
> it's probably that foreign_keys in your relationship there, which appears to
> refer to user_profiles.c.id. that's the column which is referred to here,
> and that parameter would instead be referring to the "user_id" column, i.e.
> the one that has the foreign key back to the parent row. It's equivalent to
> the column that would have ForeignKey set up on it here; I guess you have
> some multiple foreign keys happening here? tg_user.user_id is not the same
> as UserProfile.id ? This suggests some potential design problems, what is
> the value of JournalEntries.user_id if it points to row "3" in
> tg_user.user_id and row "5" in user_profile.id ?
The table tg_user only contains the authentication/access data for the user,
and is queried extremely frequently. The table user_profile contains, well
everything else in the profile that isn't needed very often. For any user with
user_id n, that user's user_profile id is also n.
Easy Fix though once you pointed out that was the problem.
Dropped the second relationship, and used joined table inheritance without a
discriminator, and the orm is now happy.
Still confused about how it ended getting a uselist=False on the backref for
that tho.
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