所以我是这个 python 和 sqlalchemy 的新手。我需要一些继承方面的帮助,或者可能需要一个 mixin(但更确切地说是继承)。
我有一些伪代码,但我并没有真正取得任何进展:
Base = declarative_base()
class ModelBase(Base):
"""Base model that only defines last_updated"""
__tablename__ = 'doesnotexistandtheclassshouldnotbeinstantiated'
#all tables inheriting from ModelBase will have this column
last_updated = Column(DateTime)
def __init__(self, last_updated):
self.last_updated = last_updated
class User(ModelBase):
"""Defines the user but should also have the last_updated inherited from ModelBase"""
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
def __init__(self, ....):
ModelBase.__init__(last_updated)
我希望所有从 ModelBase 继承的表也有 last_updated。我该怎么做?
更新代码:
class BaseUserMixin(object):
"""Base mixin for models using stamped data"""
@declared_attr
def last_updated(cls):
return Column(DateTime)
@declared_attr
def last_updated_by(cls):
return Column(String)
def __init__(self, last_updated, last_updated_by):
self.last_updated = last_updated
self.last_updated_by = last_updated_by
Base = declarative_base(cls=BaseUserMixin)
class User(Base):
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
name = Column(String)
email = Column(String)
fullname = Column(String)
password = Column(String)
enabled = Column(Boolean)
def __init__(self, name, fullname, password, email, last_updated, last_updated_by):
self.name = name
self.fullname = fullname
self.password = password
self.email = email
# goes wrong here
super(User, self).__init__(last_updated, last_updated_by)
def __repr__(self):
return "<User('%', '%', '%', '%', '%', '%')>"\
% (self.name,
self.fullname,
self.password,
self.email,
self.last_updated,
self.last_updated_by
)
错误是:
_declarative_constructor() takes exactly 1 argument (3 given)
可能是什么问题?我认为它可以正常工作,但是当重新运行调试器时它失败了。
最佳答案
解决方案是declared_attr
;它将在 DeclarativeMeta 出现的任何时候被调用并添加到实例中:
编辑:declarative
自动提供的__init__
不能调用super()
。如果你想要它,它必须是last,唯一的方法就是使用常规的 mixin。
import datetime
from sqlalchemy import Column, DateTime, Integer, String
from sqlalchemy.ext.declarative import declared_attr, declarative_base
class BaseMixin(object):
@declared_attr
def last_updated(cls):
return Column(DateTime)
def __init__(self, last_updated, *args, **kwargs):
super(BaseMixin, self).__init__(last_updated=datetime.datetime.now(), *args, **kwargs)
print "BaseMixin.__init__"
self.last_updated = last_updated
ModelBase = declarative_base()
请注意,mixin 必须放在第一位!
class User(BaseMixin, ModelBase):
"""Defines the user but should also have the last_updated inherited from ModelBase"""
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
username = Column(String)
def __init__(self, *args, **kwargs):
super(User, self).__init__(last_updated=datetime.datetime.now(), *args, **kwargs)
print "User.__init__"
if __name__ == '__main__':
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
engine = create_engine('sqlite:///:memory:', echo=True)
ModelBase.metadata.create_all(engine)
user = User(username='alice')
Session = sessionmaker(engine)
session = Session()
session.add(user)
session.commit()
但是;您确定要首先为此使用 __init__
吗? __init__
在查询返回对象时不会被调用;而您真正想要的是在列被修改时立即更改。这已经融入到 Column()
中:
from sqlalchemy import func
class BaseMixin(object):
@declared_attr
def created_date(cls):
return Column(DateTime, default=func.now())
@declared_attr
def modified_date(cls):
return Column(DateTime, default=func.now(), onupdate=func.now())
回到使用 cls=
参数
ModelBase = declarative_base(cls=BaseMixin)
class User(ModelBase):
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
username = Column(String)
if __name__ == '__main__':
engine = create_engine('sqlite:///:memory:', echo=True)
ModelBase.metadata.create_all(engine)
user = User(username='alice')
Session = sessionmaker(engine)
session = Session()
session.add(user)
session.commit()
session = Session()
sameuser = session.query(User).one()
sameuser.username = 'bob'
session.commit()
关于sqlalchemy 中的 python 继承,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/15534147/