以下是Adjacency List + Inheritance的示例。这可以按预期工作，但如果我尝试在另一个模型Mammut中使用它作为一种关系，它会抛出这个错误：
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'
守则：
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()))
答案 0 :(得分：1)
具体的继承可能非常困难，而AbstractConcreteBase本身也存在0.9中的错误，这些错误会妨碍使用这种精心设计的映射。
使用1.0（未发布，使用git master），我可以得到如下主要元素：
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