Aleksander Siewierski wrote:
> 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),
> }
> )
this pattern is described here:
http://www.sqlalchemy.org/docs/mappers.html#rows-that-point-to-themselves-mutually-dependent-rows
>
> 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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>
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