Python 如何为从sqlalchemy声明性基扩展而来的类定义元类
我使用:Python 2.6和sqlalchemy 0.6.1 这就是我想做的:Python 如何为从sqlalchemy声明性基扩展而来的类定义元类,python,dynamic,attributes,sqlalchemy,metaclass,Python,Dynamic,Attributes,Sqlalchemy,Metaclass,我使用:Python 2.6和sqlalchemy 0.6.1 这就是我想做的: from sqlalchemy.types import ( Integer, String, Boolean ) from sqlalchemy.ext.declarative import declarative_base Base = declarative_base() class SampleMeta(type): def __new__(cls, name, base
from sqlalchemy.types import (
Integer,
String,
Boolean
)
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class SampleMeta(type):
def __new__(cls, name, bases, attrs):
attrs.update({ 'id': Column('Id', Integer, primary_key=True),
'name': Column('Name', String),
'description': Column('Description', String),
'is_active': Column('IsActive', Boolean)
})
return super(SampleMeta, cls).__new__(cls, name, bases, attrs)
class Sample(Base):
__tablename__ = 'Sample'
__table_args__ = {'useexisting': True}
__metaclass__ = SampleMeta
def __init__(self, id, name, description, is_active):
self.id = id
self.name = name
self.description = description
self.is_active = is_active
def __repr__(self):
return "<(%d, '%s', '%s', %r)>" % (self.id, self.name, self.description, self.isactive)
现在,如果我使用
class Sample(object)
而不是
class Sample(Base)
它工作得非常好
我需要动态更新类的属性。因此,我将使用动态属性和列名。我需要上面的代码才能到达那里
请帮助要使用元类,在这种情况下,元类必须派生自声明词
DeclaredMeta
。但是这个用例不需要元类。使用:
从sqlalchemy.types导入(
整数,
一串
布尔值
)
从sqlalchemy.ext.declarative导入声明性基础
从sqlalchemy导入列
Base=声明性_Base()
类SampleMixin(对象):
id=列(“id”,整数,主键=真)
名称=列(“名称”,字符串)
描述=列(“描述”,字符串)
is_active=列(“IsActive”,布尔值)
类样本(SampleMixin,基):
__tablename_uu='Sample'
__表_args_uu={'useexisting':True}
定义初始化(自我、id、名称、描述,处于活动状态):
self.id=id
self.name=名称
self.description=描述
self.is_active=处于活动状态
定义报告(自我):
返回“%”(self.id,self.name,
self.description,self.isactive)
从sqlalchemy导入选择
打印选择([Sample.id,Sample.name])
如果zzzeek提出多重继承无法解决您的问题,请尝试从DeclarativeMeta继承元类:
来自sqlalchemy.ext.declarative导入declarative_base,DeclarativeMeta
Base=声明性_Base()
类SampleMeta(DeclarativeMeta):
#...
类别样本(基本):
__元类\样本元
#...
class Sample(Base)
from sqlalchemy.types import (
Integer,
String,
Boolean
)
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column
Base = declarative_base()
class SampleMixin(object):
id = Column("Id", Integer, primary_key=True)
name = Column("Name", String)
description = Column("Description", String)
is_active = Column("IsActive", Boolean)
class Sample(SampleMixin, Base):
__tablename__ = 'Sample'
__table_args__ = {'useexisting': True}
def __init__(self, id, name, description, is_active):
self.id = id
self.name = name
self.description = description
self.is_active = is_active
def __repr__(self):
return "<(%d, '%s', '%s', %r)>" % (self.id, self.name,
self.description, self.isactive)
from sqlalchemy import select
print select([Sample.id, Sample.name])