我正在尝试为 SQLalchemy 编写一个 mixin，它将在目标类上定义父/子自引用邻接关系。我正在使用 flask.ext.appbuilder用于项目脚手架。我的混合看起来像:
import inflection
from sqlalchemy import Column, ForeignKey, Integer
from sqlalchemy.ext.declarative import declared_attr
from sqlalchemy.orm import backref, relationship
class SimpleTreeBaseMixin(NameBaseMixin):
"""A mixin which organizes target class in a simple tree structure.
Bases:
.basemixins.NameBaseMixin
Attributes:
SEPARATOR (str): Separator used to divide full name.
parent_id (Optional[int]): Primary key of parent object (if any).
parent (obj): The parent object.
children (list[obj]): Collection of related children objects
"""
SEPARATOR = '.'
@declared_attr
def parent_id(cls):
fk = '{}.id'.format(inflection.tableize(cls.__name__))
return Column(Integer, ForeignKey(fk))
@declared_attr
def children(cls):
return relationship(cls.__name__,
backref=backref('parent', remote_side=cls.id),
cascade='all, delete-orphan')
def __init__(self):
super(SimpleTreeMixin, self).__init__()
def __repr__(self):
return self.full_name
@property
def full_name(self):
if self.parent:
return self.parent.full_name + self.SEPARATOR + self.name
else:
return self.name
但是，当我将此 mixin 应用于以下类时(请注意属性 id、name 和 notes 以及__tablename__ 来自 NameBaseMixin):
from flask.ext.appbuilder import Model
class PartyCategory(SimpleTreeBaseMixin, Model):
"""Represent a party category.
Categories can be put into a tree structure by defining parent and
children PartyCategory objects.
Bases:
.basemixins.SimpleTreeBaseMixin
flask.ext.appbuilder.Model
Attributes:
id (int): Primary key of category.
name (str): Name of category.
parent_id (Optional[int]): Primary key of parent object (if any).
parent (obj): The parent object.
children (list[obj]): Collection of related children objects.
notes (Optional[str]): internal notes about given object.
"""
def __init__(self):
super(PartyCategory, self).__init__()
然后尝试构建数据库，我得到一个sqlalchemy.exc.ArgumentError:
Traceback (most recent call last):
File "run.py", line 4, in <module>
from app import app
File "C:\Code\Projects\Fluffheads\app\__init__.py", line 42, in <module>
from . import views
File "C:\Code\Projects\Fluffheads\app\views.py", line 53, in <module>
class PartyView(ExtendedModelView):
File "C:\Code\Projects\Fluffheads\app\views.py", line 57, in PartyView
datamodel = SQLAInterface(Party)
File "C:\Python27\lib\site-packages\flask_appbuilder\models\sqla\interface.py", line 46, in __init__
for prop in sa.orm.class_mapper(obj).iterate_properties:
File "C:\Python27\lib\site-packages\sqlalchemy\orm\base.py", line 421, in class_mapper
mapper = _inspect_mapped_class(class_, configure=configure)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\base.py", line 400, in _inspect_mapped_class
mapper._configure_all()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line 1167, in _configure_all
configure_mappers()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line 2756, in configure_mappers
mapper._post_configure_properties()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line 1710, in _post_configure_properties
prop.init()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\interfaces.py", line 183, in init
self.do_init()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\relationships.py", line 1616, in do_init
self._generate_backref()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\relationships.py", line 1847, in _generate_backref
mapper._configure_property(backref_key, relationship)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line 1613, in _configure_property
prop.init()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\interfaces.py", line 183, in init
self.do_init()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\relationships.py", line 1613, in do_init
self._setup_join_conditions()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\relationships.py", line 1688, in _setup_join_conditions
can_be_synced_fn=self._columns_are_mapped
File "C:\Python27\lib\site-packages\sqlalchemy\orm\relationships.py", line 1965, in __init__
self._check_remote_side()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\relationships.py", line 2433, in _check_remote_side
'the relationship.' % (self.prop, ))
sqlalchemy.exc.ArgumentError: Relationship PartyCategory.parent could not determine any unambiguous local/remote column pairs based on join condition
and remote_side arguments. Consider using the remote() annotation to accurately mark those elements of the join condition that are on the remote side
of the relationship.
我还尝试将 remote_side 作为字符串传递，即 remote_side='cls.id' 但这会抛出一个 sqlalchemy .exc.InvalidRequestError:
Traceback (most recent call last):
File "run.py", line 4, in <module>
from app import app
File "C:\Code\Projects\Fluffheads\app\__init__.py", line 42, in <module>
from . import views
File "C:\Code\Projects\Fluffheads\app\views.py", line 53, in <module>
class PartyView(ExtendedModelView):
File "C:\Code\Projects\Fluffheads\app\views.py", line 57, in PartyView
datamodel = SQLAInterface(Party)
File "C:\Python27\lib\site-packages\flask_appbuilder\models\sqla\interface.py", line 46, in __init__
for prop in sa.orm.class_mapper(obj).iterate_properties:
File "C:\Python27\lib\site-packages\sqlalchemy\orm\base.py", line 421, in class_mapper
mapper = _inspect_mapped_class(class_, configure=configure)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\base.py", line 400, in _inspect_mapped_class
mapper._configure_all()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line 1167, in _configure_all
configure_mappers()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line 2756, in configure_mappers
mapper._post_configure_properties()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line 1710, in _post_configure_properties
prop.init()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\interfaces.py", line 183, in init
self.do_init()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\relationships.py", line 1616, in do_init
self._generate_backref()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\relationships.py", line 1847, in _generate_backref
mapper._configure_property(backref_key, relationship)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line 1613, in _configure_property
prop.init()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\interfaces.py", line 183, in init
self.do_init()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\relationships.py", line 1612, in do_init
self._process_dependent_arguments()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\relationships.py", line 1637, in _process_dependent_arguments
setattr(self, attr, attr_value())
File "C:\Python27\lib\site-packages\sqlalchemy\ext\declarative\clsregistry.py", line 293, in __call__
(self.prop.parent, self.arg, n.args[0], self.cls)
sqlalchemy.exc.InvalidRequestError: When initializing mapper Mapper|PartyCategory|party_categories, expression 'cls.id' failed to locate a name ("name
'cls' is not defined"). If this is a class name, consider adding this relationship() to the <class 'app.models.party.PartyCategory'> class after both
dependent classes have been defined.
如何正确构建children 关系，以便将其应用于目标类？
最佳答案
因此，简单的解决方案是将父关系的 remote_side 作为带有类名 的字符串传递，如下所示:
@declared_attr
def children(cls):
return relationship(
cls.__name__,
backref=backref(
'parent',
remote_side='{}.id'.format(cls.__name__)
),
cascade='all, delete-orphan'
)
关于python - 如何正确构建自引用 SQLalchemy 邻接列表混合，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/34363562/