[英]SQLAlchemy: How to make a hybrid_property a declared_attr?
我希望能夠使用不同的參數調用Duration.create_duration_field()
並在我的 class 上創建多個hybrid_property
。 唯一的區別是每個時間戳都會減去不同的時間戳。
當然使用declarative_attr
不是必需的,但我需要屬性是hybrid_property
。
import datetime
from sqlalchemy import create_engine, MetaData
from sqlalchemy import Column, String, DateTime, Integer
from sqlalchemy.ext.declarative import declarative_base, declared_attr
from sqlalchemy.ext.hybrid import hybrid_property
from sqlalchemy.orm import sessionmaker
metadata = MetaData()
Base = declarative_base(metadata=metadata)
class Duration(Base):
__tablename__ = "duration"
pk = Column(Integer, primary_key=True)
name = Column(String, nullable=False)
notes = Column(String)
timestamp_initiated = Column(DateTime,
default=datetime.datetime.now(),
nullable=False)
timestamp_done = Column(DateTime)
def __unicode__(self):
return self.name
@declared_attr
def duration(cls):
return cls.create_duration_field("initiated", "done")
@classmethod
def create_duration_field(cls, start, end):
@hybrid_property
def duration(obj):
getattr(obj, "timestamp_%s" % end) - getattr(obj, "timestamp_%s" % start)
@duration.expression
def duration(cls):
return getattr(cls, "timestamp_%s" % end) - getattr(cls, "timestamp_%s" % start)
return duration
engine = create_engine('sqlite:///:memory:', echo=True)
metadata.create_all(engine)
Session = sessionmaker(bind=engine)
session = Session()
duration = Duration(name="Test", timestamp_done=datetime.datetime.now() + datetime.timedelta(seconds=25))
session.add(duration)
session.commit()
assert isinstance(duration.duration, datetime.timedelta)
目前duration.duration
是對hybrid_property
的引用
<sqlalchemy.ext.hybrid.hybrid_property object at 0x1d02190>
我已經運行了腳本並且沒問題(0.9.6)。 您只需要更改以下代碼:
@hybrid_property
def duration(obj):
getattr(obj, "timestamp_%s" % end) - getattr(obj, "timestamp_%s" % start)
至:
@hybrid_property
def duration(obj):
return getattr(obj, "timestamp_%s" % end) - getattr(obj, "timestamp_%s" % start)
結果:
duration.duration = 0:00:25.017861 datetime.timedelta(0, 25, 17861) <type 'datetime.timedelta'>
我還在 0.6,所以我不能嘗試你的花哨屬性。 :)
但不是
class Duration(Base):
# [...]
@declared_attr
def duration(cls):
return cls.create_duration_field("initiated", "done")
你可以嘗試類似的東西:
class Duration(Base):
duration = declared_attr(create_duration_field("initiated", "done"))
並將您的 *create_duration_field* 類方法移出 class。 這樣你也可以在不同的類上重用它。 也許declared_attr也應該移到*create_duration_field* 中,您必須在那里進行試驗。
一個例子就是我一直使用的這個小東西:
def constructor(**kw):
"""Creates a class constructor class method"""
def load(cls):
query = cls.query
return query.filter_by(**kw).one()
return classmethod(load)
你會像這樣使用它:
class SomeModel(Base):
SomeInstance = constructor(primary_key=17)
instance = SomeModel.SomeInstance()
希望你能明白。
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.