如何在sqlalchemy.orm.synonym中使用描述符

时间:2014-04-23 04:13:13

标签: sqlalchemy

我有这样的代码正常工作:

def get_timestamp(ts):
    return datetime.utcfromtimestamp(ts)

def set_timestamp(dt):
    return time.mktime(dt.timetuple())

class Group(Base):
    __tablename__ = 'group'
    _created = Column('created', Integer, nullable=False)

    @property
    def created(self):
        return get_timestamp(self._created)
    @created.setter
    def created(self, value):
        self._created = set_timestamp(value)

我想要一些这样的代码,但它不起作用:

created = synonym('_created',
                  descriptor=property(get_timestamp,
                                      set_created))

因为它总是以self作为第一个参数传递。

我希望在我的事业项目中使用get_timestampset_timestamp。所以我不打算让他们成为班级的方法,而是独立的功能。

我怎样才能做到这一点?

编辑:我会接受Option2,仍然可以接受其他答案。

2 个答案:

答案 0 :(得分:1)

选项-1 :以下代码应该有效(您无需为了定义self而拥有一个类):

def pget_timestamp(self):
    return datetime.utcfromtimestamp(self._created)

def pset_timestamp(self, dt):
    self._created = time.mktime(dt.timetuple())

class Group(Base):
    __tablename__ = 'group'
    id = Column(Integer, primary_key=True)
    _created = Column('created', Integer, nullable=False)

    created = synonym(_created,
            descriptor=property(pget_timestamp, pset_timestamp),
            )

选项-2 :如果您在许多课程中确实需要相同的内容,请使用Mixins

from sqlalchemy.ext.declarative import declared_attr
class _CreatedMixin(object):
    _created = Column('created', Integer, nullable=False)

    def pget_timestamp(self):
        return datetime.utcfromtimestamp(self._created)

    def pset_timestamp(self, dt):
        self._created = time.mktime(dt.timetuple())

    @declared_attr
    def created(cls):
        return synonym('_created',
            descriptor=property(cls.pget_timestamp, cls.pset_timestamp),
            )


class Group(_CreatedMixin, Base):
    # @note: adding *_CreatedMixin* to bases defines both the column and the synonym
    __tablename__ = 'group'
    id = Column(Integer, primary_key=True)

或者,如果这是针对您的课程的所有,那么您可以为所有模型制作_CreatedMixin基类:

Base = declarative_base(engine, cls=_CreatedMixin)
class Group(Base):
    __tablename__ = 'group'
    id = Column(Integer, primary_key=True)

选项-3 :您可以使用Hybrid Attributes

执行上述任何操作

注意:使您的set / get函数同步:两者都使用或不使用启用UTC的功能。目前(除非你是UTC-0)将一个值设置为created将不会返回相同的值。

答案 1 :(得分:0)

我现在正在使用不同的实现。它与原始标题无关,但如果您需要它。

使用sqlalchemy.types.TypeDecorator Defining a table with sqlalchemy with a mysql unix timestamp

class UTCTimestampType(TypeDecorator):
    impl = Integer

    def process_bind_param(self, value, dialect):
        if value is None:
            return None  # support nullability
        elif isinstance(value, datetime):
            return int(time.mktime(value.timetuple()))
        raise ValueError("Can operate only on datetime values. Offending value type: {0}".format(type(value).__name__))

    def process_result_value(self, value, dialect):
        if value is not None:  # support nullability
            return datetime.fromtimestamp(float(value))

class ModelA(Base):
    __tablename__ = 'model_a'
    id = Column(Integer, primary_key=True)
    created = Column(UTCTimestampType, nullable=False)

关于alembic的问题Alembic: How to migrate custom type in a model?

# manually change the line
sa.Column('created', sa.UTCTImestampType(), nullable=False),
# to
sa.Column('created', sa.Integer(), nullable=False),