I am attempting to extend the self referential example in the docs
http://www.sqlalchemy.org/docs/index.myt?paged=no#advdatamapping_circular
by adding properties 'prev_sibling' and 'next_sibling'. (See attached
script)
When run, the following exception is raised:
Traceback (most recent call last):
File "tree.py", line 79, in ?
session.flush()
File "build/bdist.linux-i686/egg/sqlalchemy/orm/session.py", line 234,
in flush
File "build/bdist.linux-i686/egg/sqlalchemy/orm/unitofwork.py", line
197, in flush
File "build/bdist.linux-i686/egg/sqlalchemy/orm/unitofwork.py", line
359, in execute
File "build/bdist.linux-i686/egg/sqlalchemy/orm/unitofwork.py", line
407, in _sort_dependencies
File "build/bdist.linux-i686/egg/sqlalchemy/orm/unitofwork.py", line
395, in sort_hier
File "build/bdist.linux-i686/egg/sqlalchemy/orm/unitofwork.py", line
800, in _sort_circular_dependencies
File "build/bdist.linux-i686/egg/sqlalchemy/orm/topological.py", line
139, in sort
sqlalchemy.exceptions.FlushError: Circular dependency detected
{<Node(path=first)> (idself=1079711436): {<Node(path=second)>
(idself=1079711468): True, <Node(path=root)> (idself=1079711404):
True}, <Node(path=root)> (idself=1079711404): {<Node(path=second)>
(idself=1079711468): True, <Node(path=first)> (idself=1079711436):
True}, <Node(path=second)> (idself=1079711468): {<Node(path=first)>
(idself=1079711436): True, <Node(path=root)> (idself=1079711404): True}}[]
I am doing something wrong? If so can someone point me in the right
direction ...
Thanks,
Nick
import sqlalchemy.mods.threadlocal
from sqlalchemy import *
engine = create_engine('sqlite:///:memory:', echo=True);
metadata = BoundMetaData(engine)
node_table = Table('node', metadata,
Column('id', Integer, primary_key=True),
Column('path', String(50), nullable=False),
Column('parent_id', Integer, ForeignKey('node.id'), nullable=True),
Column('prev_sibling_id', Integer, ForeignKey('node.id'), nullable=True),
Column('next_sibling_id', Integer, ForeignKey('node.id'), nullable=True)
)
class Node(object):
def __init__(self, path=''):
self.path = path
def has_child_nodes(self):
return len(self.children) == 0
def append_child(self, child):
try:
lc = self.children[len(self.children) - 1]
except IndexError, e:
lc = None
self.children.append(child)
child.parent = self
if lc is not None:
lc.next_sibling = child
child.previous_sibling = lc
def __repr__(self):
return '<Node(path=%s)>' % self.path
n_mapper = mapper(Node, node_table, properties={
'parent': relation(
Node,
lazy=True,
primaryjoin=node_table.c.parent_id==node_table.c.id,
uselist=False
),
'children': relation(
Node,
primaryjoin=node_table.c.id==node_table.c.parent_id,
lazy=True,
cascade="all, delete-orphan"
),
'previous_sibling': relation(
Node,
primaryjoin=node_table.c.prev_sibling_id==node_table.c.id,
lazy=True,
uselist=False
),
'next_sibling': relation(
Node,
primaryjoin=node_table.c.next_sibling_id==node_table.c.id,
lazy=True,
uselist=False
)
})
if __name__ == '__main__':
node_table.create()
root = Node('root')
first = Node('first')
second = Node('second')
root.append_child(first)
root.append_child(second)
print first==second.previous_sibling
session = objectstore.session
session.flush()
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