Adjacency list + Abstract Base Class Inheritance used in relationship - sqlalchemy

Question

Following is a example for Adjacency List + Inheritance. This works as expected but if i try to use it in a another Model Mammut as a relationship it throws me this error:
Traceback (most recent call last):
File "bin/py", line 73, in <module>
exec(compile(__file__f.read(), __file__, "exec"))
File "../adjacency_list.py", line 206, in <module>
create_entries(IntTreeNode)
File "../adjacency_list.py", line 170, in create_entries
mut.nodes.append(node)
File "/home/xxx/.buildout/eggs/SQLAlchemy-0.9.8-py3.4-linux-x86_64.egg/sqlalchemy/orm/dynamic.py", line 304, in append
attributes.instance_dict(self.instance), item, None)
File "/home/xxx/.buildout/eggs/SQLAlchemy-0.9.8-py3.4-linux-x86_64.egg/sqlalchemy/orm/dynamic.py", line 202, in append
self.fire_append_event(state, dict_, value, initiator)
File "/home/xxx/.buildout/eggs/SQLAlchemy-0.9.8-py3.4-linux-x86_64.egg/sqlalchemy/orm/dynamic.py", line 99, in fire_append_event
value = fn(state, value, initiator or self._append_token)
File "/home/xxx/.buildout/eggs/SQLAlchemy-0.9.8-py3.4-linux-x86_64.egg/sqlalchemy/orm/attributes.py", line 1164, in emit_backref_from_collection_append_event
child_impl.append(
AttributeError: '_ProxyImpl' object has no attribute 'append'
The Code:
from sqlalchemy import (Column, ForeignKey, Integer, String, create_engine,
Float)
from sqlalchemy.orm import (Session, relationship, backref, joinedload_all)
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm.collections import attribute_mapped_collection
from sqlalchemy.ext.declarative import declared_attr, AbstractConcreteBase
Base = declarative_base()
class Mammut(Base):
__tablename__ = "mammut"
id = Column(Integer, primary_key=True)
nodes = relationship(
'TreeNode',
backref='mammut',
lazy='dynamic',
cascade="all, delete-orphan",
#viewonly=True
)
class TreeNode(AbstractConcreteBase, Base):
id = Column(Integer, primary_key=True)
name = Column(String(50), nullable=False)
depth = Column(Integer, default=0)
data_type = Column(String(50))
#declared_attr
def mammut_id(cls):
return Column(Integer, ForeignKey('mammut.id'))
#declared_attr
def __tablename__(cls):
return cls.__name__.lower()
#declared_attr
def __mapper_args__(cls):
ret = {}
if cls.__name__ != "TreeNode":
ret = {'polymorphic_identity': cls.__name__,
'concrete': True,
# XXX redundant makes only sense if we use one table
'polymorphic_on': cls.data_type}
return ret
#declared_attr
def parent_id(cls):
_fid = '%s.id' % cls.__name__.lower()
return Column(Integer, ForeignKey(_fid))
#declared_attr
def children(cls):
_fid = '%s.id' % cls.__name__
return relationship(cls.__name__,
# cascade deletions
cascade="all, delete-orphan",
# many to one + adjacency list - remote_side
# is required to reference the 'remote'
# column in the join condition.
backref=backref("parent", remote_side=_fid),
# children will be represented as a dictionary
# on the "name" attribute.
collection_class=attribute_mapped_collection(
'name'),
)
def get_path(self, field):
if self.parent:
return self.parent.get_path(field) + [getattr(self, field)]
else:
return [getattr(self, field)]
#property
def name_path(self):
# XXX there is no way to query for it except we add a function with a
# cte (recursive query) to our database see [1] for it
# https://stackoverflow.com/questions/14487386/sqlalchemy-recursive-hybrid-property-in-a-tree-node
return '/'.join(self.get_path(field='name'))
def __init__(self, name, value=None, parent=None):
self.name = name
self.parent = parent
self.depth = 0
self.value = value
if self.parent:
self.depth = self.parent.depth + 1
def __repr__(self):
ret = "%s(name=%r, id=%r, parent_id=%r, value=%r, depth=%r, " \
"name_path=%s data_type=%s)" % (
self.__class__.__name__,
self.name,
self.id,
self.parent_id,
self.value,
self.depth,
self.name_path,
self.data_type
)
return ret
def dump(self, _indent=0):
return " " * _indent + repr(self) + \
"\n" + \
"".join([
c.dump(_indent + 1)
for c in self.children.values()]
)
class IntTreeNode(TreeNode):
value = Column(Integer)
class FloatTreeNode(TreeNode):
value = Column(Float)
miau = Column(String(50), default='zuff')
def __repr__(self):
ret = "%s(name=%r, id=%r, parent_id=%r, value=%r, depth=%r, " \
"name_path=%s data_type=%s miau=%s)" % (
self.__class__.__name__,
self.name,
self.id,
self.parent_id,
self.value,
self.depth,
self.name_path,
self.data_type,
self.miau
)
return ret
if __name__ == '__main__':
engine = create_engine('sqlite:///', echo=True)
def msg(msg, *args):
msg = msg % args
print("\n\n\n" + "-" * len(msg.split("\n")[0]))
print(msg)
print("-" * len(msg.split("\n")[0]))
msg("Creating Tree Table:")
Base.metadata.create_all(engine)
session = Session(engine)
def create_entries(Cls):
node = Cls('rootnode', value=2)
Cls('node1', parent=node)
Cls('node3', parent=node)
node2 = Cls('node2')
Cls('subnode1', parent=node2)
node.children['node2'] = node2
Cls('subnode2', parent=node.children['node2'])
msg("Created new tree structure:\n%s", node.dump())
msg("flush + commit:")
# XXX this throws the error
mut = Mammut()
mut.nodes.append(node)
session.add(mut)
session.add(node)
session.commit()
msg("Tree After Save:\n %s", node.dump())
Cls('node4', parent=node)
Cls('subnode3', parent=node.children['node4'])
Cls('subnode4', parent=node.children['node4'])
Cls('subsubnode1', parent=node.children['node4'].children['subnode3'])
# remove node1 from the parent, which will trigger a delete
# via the delete-orphan cascade.
del node.children['node1']
msg("Removed node1. flush + commit:")
session.commit()
msg("Tree after save:\n %s", node.dump())
msg("Emptying out the session entirely, "
"selecting tree on root, using eager loading to join four levels deep.")
session.expunge_all()
node = session.query(Cls).\
options(joinedload_all("children", "children",
"children", "children")).\
filter(Cls.name == "rootnode").\
first()
msg("Full Tree:\n%s", node.dump())
# msg("Marking root node as deleted, flush + commit:")
# session.delete(node)
# session.commit()
create_entries(IntTreeNode)
create_entries(FloatTreeNode)
nodes = session.query(TreeNode).filter(
TreeNode.name == "rootnode").all()
for idx, n in enumerate(nodes):
msg("Full (%s) Tree:\n%s" % (idx, n.dump()))

Answer 1

concrete inheritance can be very difficult, and AbstractConcreteBase itself has bugs in 0.9 which get in the way of elaborate mappings like this from being used.
Using 1.0 (not released, use git master), I can get the major elements going as follows:
from sqlalchemy import Column, String, Integer, create_engine, ForeignKey, Float
from sqlalchemy.orm import Session, relationship
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm.collections import attribute_mapped_collection
from sqlalchemy.ext.declarative import declared_attr, AbstractConcreteBase
Base = declarative_base()
class Mammut(Base):
__tablename__ = "mammut"
id = Column(Integer, primary_key=True)
nodes = relationship(
'TreeNode',
lazy='dynamic',
back_populates='mammut',
)
class TreeNode(AbstractConcreteBase, Base):
id = Column(Integer, primary_key=True)
name = Column(String)
#declared_attr
def __tablename__(cls):
if cls.__name__ == 'TreeNode':
return None
else:
return cls.__name__.lower()
#declared_attr
def __mapper_args__(cls):
return {'polymorphic_identity': cls.__name__, 'concrete': True}
#declared_attr
def parent_id(cls):
return Column(Integer, ForeignKey(cls.id))
#declared_attr
def mammut_id(cls):
return Column(Integer, ForeignKey('mammut.id'))
#declared_attr
def mammut(cls):
return relationship("Mammut", back_populates="nodes")
#declared_attr
def children(cls):
return relationship(
cls,
back_populates="parent",
collection_class=attribute_mapped_collection('name'),
)
#declared_attr
def parent(cls):
return relationship(
cls, remote_side="%s.id" % cls.__name__,
back_populates='children')
class IntTreeNode(TreeNode):
value = Column(Integer)
class FloatTreeNode(TreeNode):
value = Column(Float)
miau = Column(String(50), default='zuff')
e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)
session = Session(e)
root = IntTreeNode(name='root')
IntTreeNode(name='n1', parent=root)
n2 = IntTreeNode(name='n2', parent=root)
IntTreeNode(name='n2n1', parent=n2)
m1 = Mammut()
m1.nodes.append(n2)
m1.nodes.append(root)
session.add(root)
session.commit()
session.close()
root = session.query(TreeNode).filter_by(name='root').one()
print root.children