Hi!,
I have two entities: Channel and Track. Track has a reference to
Channel (channel field - Track is played on this Channel), and Channel
has a reference to Track (last_track field - last planned Track for
Channel). So definition of tables, classes and mappers is:
import sqlalchemy
from sqlalchemy.orm import *
from sqlalchemy.schema import *
from sqlalchemy.types import *
sqlalchemy_config = {
'url' : 'mysql://...',
'echo': True,
'pool_recycle': 600,
'convert_unicode' : True,
}
ENGINE = sqlalchemy.engine.engine_from_config(sqlalchemy_config, '')
METADATA = sqlalchemy.schema.MetaData()
METADATA.bind = ENGINE
session_maker = sqlalchemy.orm.sessionmaker(autoflush=True,
transactional=True, bind=ENGINE)
SESSION = sqlalchemy.orm.scoped_session(session_maker)
class Channel(object):
def __init__(self, name):
self.name = name
class Track(object):
def __init__(self, title):
self.title = title
channel_t = Table(
'channels',
METADATA,
Column('id', Integer, primary_key=True),
Column('name', Unicode(256)),
Column('last_track_id', Integer, ForeignKey('tracks.id')),
mysql_engine='InnoDB',
mysql_charset='utf8'
)
track_t = Table(
'tracks',
METADATA,
Column('id', Integer, primary_key=True),
Column('channel_id', Integer, ForeignKey('channels.id'),
nullable=False),
Column('title', Unicode(256)),
mysql_engine='InnoDB',
mysql_charset='utf8'
)
mapper(Channel, channel_t, properties = {
'last_track': relation(Track,
primaryjoin=channel_t.c.last_track_id == track_t.c.id),
}
)
mapper(Track, track_t, properties={
'channel': relation(Channel,
primaryjoin=track_t.c.channel_id == channel_t.c.id),
}
)
channel1 = SESSION.query(Channel).get(1)
track1 = Track('Track 1')
track1.channel = channel1
channel1.last_track = track1
SESSION.add(track1)
SESSION.commit()
and when I try to commit this, I have following error:
Traceback (most recent call last):
File cml.py, line 75, in module
SESSION.commit()
File /usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.5.8-
py2.6.egg/sqlalchemy/orm/scoping.py, line 127, in do
return getattr(self.registry(), name)(*args, **kwargs)
File /usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.5.8-
py2.6.egg/sqlalchemy/orm/session.py, line 671, in commit
self.transaction.commit()
File /usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.5.8-
py2.6.egg/sqlalchemy/orm/session.py, line 378, in commit
self._prepare_impl()
File /usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.5.8-
py2.6.egg/sqlalchemy/orm/session.py, line 362, in _prepare_impl
self.session.flush()
File /usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.5.8-
py2.6.egg/sqlalchemy/orm/session.py, line 1354, in flush
self._flush(objects)
File /usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.5.8-
py2.6.egg/sqlalchemy/orm/session.py, line 1432, in _flush
flush_context.execute()
File /usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.5.8-
py2.6.egg/sqlalchemy/orm/unitofwork.py, line 258, in execute
tasks = self._sort_dependencies()
File /usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.5.8-
py2.6.egg/sqlalchemy/orm/unitofwork.py, line 299, in
_sort_dependencies
for t in task._sort_circular_dependencies(self,
[self.get_task_by_mapper(i) for i in cycles]):
File /usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.5.8-
py2.6.egg/sqlalchemy/orm/unitofwork.py, line 582, in
_sort_circular_dependencies
head = topological.sort_as_tree(tuples,
object_to_original_task.iterkeys())
File /usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.5.8-
py2.6.egg/sqlalchemy/topological.py, line 59, in sort_as_tree
return _organize_as_tree(_sort(tuples, allitems,
allow_cycles=with_cycles))
File /usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.5.8-
py2.6.egg/sqlalchemy/topological.py, line 209, in _sort
raise CircularDependencyError(Circular dependency detected +
repr(edges) + repr(queue))
sqlalchemy.exc.CircularDependencyError: Circular dependency detected
[(sqlalchemy.orm.state.InstanceState object at 0x211d050,
sqlalchemy.orm.state.InstanceState object at 0x21926d0),
(sqlalchemy.orm.state.InstanceState object at 0x21926d0,
sqlalchemy.orm.state.InstanceState object at 0x211d050)][]
what is wrong with this definitions? Documentation says that
CircularDependencyError should appear only when I do topological
sorting.
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