Question

我正在尝试同时处理两件新事物，因此我们非常感谢您在简化和澄清方面的帮助。

from sqlalchemy.ext.declarative import declared_attr
from sqlalchemy import Column, Float, event

class TimeStampMixin(object):

    @declared_attr
    def __tablename__(cls):
        return cls.__name__.lower()

    created = Column(Float)
    modified = Column(Float)
    def __init__(self, created = None,
                       modified = None):
        self.created = created
        self.modified = modified

def create_time(mapper, connection, target):
    target.created = time()

#def modified_time(mapper, connection, target):
#    target.modified = time()

event.listen(TimeStampMixin, 'before_insert', create_time)
#event.listen(TimeStampMixin, 'before_update', modified_time)

所以我想创建一个我可以在任何类中应用的mixin：

class MyClass(TimeStampMixin, Base):
    etc, etc, etc

此类继承在创建时创建时间戳并在更新时创建/修改时间戳的功能。

导入时出现此错误：

raise exc.UnmappedClassError(class_)
sqlalchemy.orm.exc.UnmappedClassError: Class 'db.database.TimeStampMixin' is not mapped

aaaand我在这一点上很难过。

Answer 1

将您的侦听器附加到类方法中，它会将事件附加到子类。

class TimeStampMixin(object):
    @staticmethod
    def create_time(mapper, connection, target):
        target.created = time()

    @classmethod
    def __declare_last__(cls):
        # get called after mappings are completed
        # http://docs.sqlalchemy.org/en/rel_0_7/orm/extensions/declarative.html#declare-last
        event.listen(cls, 'before_insert', cls.create_time)

Answer 2

以下是我要对before_insert事件进行聆听的事项：向classmethod添加TimeStampMixin，注册当前类并处理设置创建时间。

E.g。

class TimeStampMixin(object):

    # other class methods

    @staticmethod
    def create_time(mapper, connection, target):
        target.created = time()

    @classmethod
    def register(cls):
        sqlalchemy.event.listen(cls, 'before_insert', cls.create_time)

这样，您可以：

轻松扩展和更改您收听的内容以及注册内容。
覆盖某些类的create_time方法
明确说明哪些方法需要设置时间戳。

您可以简单地使用它：

class MyMappedClass(TimeStampMixin, Base):
    pass

MyMappedClass.register()

简单，非常清晰，没有魔法，但仍然像你想要的那样封装。

Answer 3

你也可以这样做：

from sqlalchemy.orm.interfaces import MapperExtension

class BaseExtension(MapperExtension):
    """Base entension class for all entities """

    def before_insert(self, mapper, connection, instance):
        """ set the created_at  """
        instance.created = datetime.datetime.now()

    def before_update(self, mapper, connection, instance):
        """ set the updated_at  """
        instance.modified = datetime.datetime.now()


class TimeStampMixin(object):
    id = Column(Integer, primary_key=True, autoincrement=True)
    created = Column(DateTime())
    modified = Column(DateTime())

    __table_args__ = {
        'mysql_engine': 'InnoDB',
        'mysql_charset': 'utf8'
    }
    __mapper_args__ = { 'extension': BaseExtension() }

并定义您的类，如：

class User(TimeStampMixin, Base):

Answer 4

现代SqlAlchemy的最佳方法是将@listens_for装饰器与propagate=True一起使用。

from datetime import datetime
from sqlalchemy import Column, Float
from sqlalchemy.ext.declarative import declared_attr
from sqlalchemy.event import listens_for

class TimestampMixin():
    @declared_attr
    def created(cls):
        return Column(DateTime(timezone=True))

@listens_for(TimeStampMixin, "init", propagate=True)
def timestamp_init(target, args, kwargs):
    kwargs["created"] = datetime.utcnow()

Sqlalchemy mixins /和事件监听器

4 个答案: