我正在尝试使用基类中的单个CheckConstraint创建基本模型。当我将基类混入flask-sqlalchemy模型并尝试使用它时，我得到“无法将未命名的列添加到列集合中”。
我尝试使用不同的方式来声明此CheckConstraint 但都是由于同样的错误造成的。是什么原因引起了这个？
from sqlalchemy.ext.declarative import declared_attr
from myproject.db import db
class FilteringMixin(db.Model):
__abstract__ = True
FILTER_TYPES = {
'whitelist': 0,
'blacklist': 1,
}
@declared_attr.cascading
def filter_type(cls):
return db.Column(db.SmallInteger, nullable=False,
default=cls.FILTER_TYPES['whitelist'])
@declared_attr.cascading
def __table_args__(cls):
return (
db.CheckConstraint(cls.filter_type.in_(cls.FILTER_TYPES.values())),
)
class FilteredConnectionType(FilteringMixin, db.Model):
CONNECTION_TYPES = {
'wifi': 0,
'cellular': 1,
}
__tablename__ = 'filtered_connection_types'
id = db.Column(db.BigInteger, primary_key=True)
connection_type = db.Column(db.SmallInteger, nullable=False,
default=CONNECTION_TYPES['cellular'])
@declared_attr.cascading
def __table_args__(cls):
return (
db.CheckConstraint(cls.connection_type.in_(cls.CONNECTION_TYPES.values())),
) + FilteringMixin.__table_args__
在那之后，尝试使用它我得到：
python manage.py shell
~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/ext/declarative/api.py:173: SAWarning: Unmanaged access of declarative attribute __table_args__ from non-mapped class FilteringMixin
(desc.fget.__name__, cls.__name__))
~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/ext/declarative/api.py:173: SAWarning: Unmanaged access of declarative attribute filter_type from non-mapped class FilteringMixin
(desc.fget.__name__, cls.__name__))
Traceback (most recent call last):
File "manage.py", line 4, in <module>
from myproject import create_app, environments, scripts
File "~/myuser/myproject/myproject/__init__.py", line 9, in <module>
import models
File "~/myuser/myproject/myproject/models/__init__.py", line 13, in <module>
from .filtering_implemented import FilteredConnectionType
File "~/myuser/myproject/myproject/models/filtering_implemented.py", line 6, in <module>
class FilteredConnectionType(FilteringMixin, db.Model):
File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/flask_sqlalchemy/__init__.py", line 609, in __init__
DeclarativeMeta.__init__(self, name, bases, d)
File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/ext/declarative/api.py", line 55, in __init__
_as_declarative(cls, classname, cls.__dict__)
File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line 88, in _as_declarative
_MapperConfig.setup_mapping(cls, classname, dict_)
File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line 103, in setup_mapping
cfg_cls(cls_, classname, dict_)
File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line 131, in __init__
self._setup_table()
File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line 394, in _setup_table
**table_kw)
File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/sql/schema.py", line 416, in __new__
metadata._remove_table(name, schema)
File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py", line 60, in __exit__
compat.reraise(exc_type, exc_value, exc_tb)
File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/sql/schema.py", line 411, in __new__
table._init(name, metadata, *args, **kw)
File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/sql/schema.py", line 488, in _init
self._init_items(*args)
File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/sql/schema.py", line 72, in _init_items
item._set_parent_with_dispatch(self)
File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/sql/base.py", line 433, in _set_parent_with_dispatch
self._set_parent(parent)
File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/sql/schema.py", line 2553, in _set_parent
ColumnCollectionMixin._set_parent(self, table)
File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/sql/schema.py", line 2521, in _set_parent
self.columns.add(col)
File "~/myuser/myproject/.venv/local/lib/python2.7/site-packages/sqlalchemy/sql/base.py", line 509, in add
"Can't add unnamed column to column collection")
sqlalchemy.exc.ArgumentError: Can't add unnamed column to column collection
答案 0 :(得分：2)
我认为真正的问题在错误输出顶部的两个警告中突出显示：
.../api.py:173: SAWarning: Unmanaged access of declarative attribute __table_args__ from non-mapped class FilteringMixin
(desc.fget.__name__, cls.__name__))
而且，据我所知，它是由FilteringMixin.__table_args__使用引起的，修复方法是使用基于字符串的语法来描述约束：
class FilteringMixin(object):
FILTER_TYPES = {
'whitelist': 0,
'blacklist': 1,
}
@declared_attr
def filter_type(cls):
return db.Column(db.SmallInteger, nullable=False,
default=cls.FILTER_TYPES['whitelist'])
@declared_attr
def __table_args__(cls):
return (
db.CheckConstraint(
'filter_type in (%s)' %
','.join(str(t) for t in cls.FILTER_TYPES.values())),
)
class FilteredConnectionType(FilteringMixin, db.Model):
CONNECTION_TYPES = {
'wifi': 0,
'cellular': 1,
}
__tablename__ = 'filtered_connection_types'
# Changed to db.Integer from db.BigInteger because of SQLite
id = db.Column(db.Integer, primary_key=True)
connection_type = db.Column(db.SmallInteger, nullable=False,
default=CONNECTION_TYPES['cellular'])
@declared_attr
def __table_args__(cls):
return (
db.CheckConstraint(cls.connection_type.in_(cls.CONNECTION_TYPES.values())),
) + FilteringMixin.__table_args__
测试代码：
# saves the record with defaults
conn_type = FilteredConnectionType()
session.add(conn_type)
session.commit()
# raises an error: Check constraint failed
conn_type = FilteredConnectionType(filter_type=3)
session.add(conn_type)
session.commit()
注意：
@declared_attr.cascading，只需@declared_attr FilteringMixin我重命名了使用的基于字符串的语法来定义约束。