always use remote_side=table.c.id on the "many to one" side of a self
referential relation, in the case of declarative it would look like
"remote_side=id". See
http://www.sqlalchemy.org/docs/05/mappers.html#advdatamapping_relation_selfreferential
for information on this.
On Nov 11, 2008, at 2:15 PM, MikeCo wrote:
>
> I have a table that defines a self-referential hierarchy. My problem
> is figuring out how to specify that relationship in declarative
> syntax. From reading the documentation and looking at example
> basic_tree.py, I think I understand it when using tables and mappers,
> but can't get it right with declarative.
>
> Here is one way I tried it. Using 0.5rc2 or 0.5rc3 gives the traceback
> below on session.commit() telling me I have circular references.
>
> import sqlalchemy
> print 'SQLAlchemy version', sqlalchemy.__version__
>
> from sqlalchemy import create_engine, Column, Integer, String,
> MetaData, ForeignKey
> from sqlalchemy.ext.declarative import declarative_base
> from sqlalchemy.orm import sessionmaker, relation, backref
>
> engine = create_engine(r'sqlite:///:memory:')
> Base = declarative_base(bind=engine)
> class People(Base):
> __tablename__ = 'people'
> id = Column(Integer, primary_key=True)
> parent_id = Column(Integer, ForeignKey('people.id'))
> name = Column(String)
> parent = relation('People', cascade='all',
> backref=backref('children'))
>
> Base.metadata.create_all()
> Session = sessionmaker()
> session = Session()
>
> p1 = People(name='john')
> p2 = People(name='susie')
> p3 = People(name='joannie')
> p1.children.append(p2)
> p2.children.append(p3)
> session = Session()
> session.add(p1)
> session.commit()
>
> File "sample_recursive.py", line 30, in <module>
> session.commit()
> File "C:\Python25\lib\site-packages\sqlalchemy-0.5.0rc2-py2.5.egg
> \sqlalchemy\orm\session.py", line 670, in commit
> self.transaction.commit()
> File "C:\Python25\lib\site-packages\sqlalchemy-0.5.0rc2-py2.5.egg
> \sqlalchemy\orm\session.py", line 375, in commit
> self._prepare_impl()
> File "C:\Python25\lib\site-packages\sqlalchemy-0.5.0rc2-py2.5.egg
> \sqlalchemy\orm\session.py", line 359, in _prepare_impl
> self.session.flush()
> File "C:\Python25\lib\site-packages\sqlalchemy-0.5.0rc2-py2.5.egg
> \sqlalchemy\orm\session.py", line 1361, in flush
> self._flush(objects)
> File "C:\Python25\lib\site-packages\sqlalchemy-0.5.0rc2-py2.5.egg
> \sqlalchemy\orm\session.py", line 1431, in _flush
> flush_context.execute()
> File "C:\Python25\lib\site-packages\sqlalchemy-0.5.0rc2-py2.5.egg
> \sqlalchemy\orm\unitofwork.py", line 261, in execute
> tasks = self._sort_dependencies()
> File "C:\Python25\lib\site-packages\sqlalchemy-0.5.0rc2-py2.5.egg
> \sqlalchemy\orm\unitofwork.py", line 302, in _sort_depen
> dencies
> for t in task._sort_circular_dependencies(self,
> [self.get_task_by_mapper(i) for i in cycles]):
> File "C:\Python25\lib\site-packages\sqlalchemy-0.5.0rc2-py2.5.egg
> \sqlalchemy\orm\unitofwork.py", line 568, in _sort_circu
> lar_dependencies
> head = topological.sort_as_tree(tuples,
> object_to_original_task.keys())
> File "C:\Python25\lib\site-packages\sqlalchemy-0.5.0rc2-py2.5.egg
> \sqlalchemy\topological.py", line 58, in sort_as_tree
> return _organize_as_tree(_sort(tuples, allitems,
> allow_cycles=with_cycles))
> File "C:\Python25\lib\site-packages\sqlalchemy-0.5.0rc2-py2.5.egg
> \sqlalchemy\topological.py", line 212, in _sort
> raise CircularDependencyError("Circular dependency detected " +
> repr(edges) + repr(queue))
> sqlalchemy.exc.CircularDependencyError: Circular dependency detected
> [(<sqlalchemy.orm.identity.IdentityManagedState object
> at 0x00E80510>, <sqlalchemy.orm.identity.IdentityManagedState object
> at 0x00E80490>), (<sqlalchemy.orm.identity.IdentityMa
> nagedState object at 0x00E80490>,
> <sqlalchemy.orm.identity.IdentityManagedState object at 0x00E80510>),
> (<sqlalchemy.orm.id
> entity.IdentityManagedState object at 0x00E80490>,
> <sqlalchemy.orm.identity.IdentityManagedState object at 0x00E80C70>),
> (<
> sqlalchemy.orm.identity.IdentityManagedState object at 0x00E80C70>,
> <sqlalchemy.orm.identity.IdentityManagedState object at
> 0x00E80490>)][]
>
> --
> Mike Conley
>
> >
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