Python SQLAlchemy:Override relationship defined";订购人;在查询中
因此,我有一个模型,类似于:Python SQLAlchemy:Override relationship defined";订购人;在查询中,python,sqlalchemy,Python,Sqlalchemy,因此,我有一个模型,类似于: class Foo(model): __tablename__ = "foo" id = Column(Integer, primary_key=True) data = relationship( "FooData", cascade="all, delete-orphan", backref="foo", lazy="dynamic", order_by="d
class Foo(model):
__tablename__ = "foo"
id = Column(Integer, primary_key=True)
data = relationship(
"FooData",
cascade="all, delete-orphan",
backref="foo",
lazy="dynamic",
order_by="desc(FooData.timestamp)"
)
@property
def first_item(self):
# the problem is here:
return self.data.order_by(asc("timestamp")).first()
@property
def latest_item(self):
return self.data.first()
class FooData(Model):
__tablename__ = "foo_data"
foo_id = Column(Integer, ForeignKey("foo.id"), primary_key=True)
timestamp = Column(DateTime, primary_key=True)
actual_data = Column(Float, nullable=False)
因此,这里的first\u item
方法存在问题:如上所述定义时,SQL如下所示:
SELECT foo_data.timestamp AS foo_data_timestamp, foo_data.actual_data AS foo_data_actual_data, foo_data.foo_id AS foo_data_foo_id
FROM foo_data
WHERE :param_1 = foo_data.foo_id ORDER BY foo_data.timestamp DESC, foo_data.timestamp ASC
-- ^^^^^^^^^^^^^^^^^^^^^^
显然,查询中指定的order\u by
将附加到关系定义中指定的,而不是替换它;查询是否有办法通过覆盖原始的订单?我知道我可以直接在FooData
类上指定一个单独的查询,但如果可能的话,我希望避免这种情况。根据:
通过传递None
,可以抑制所有现有的顺序设置-这也将通过在映射器上配置来抑制任何顺序
因此,简单的解决方案是重置ORDER BY
子句,然后应用所需的。比如:
self.data.order_by(None).order_by(asc("timestamp")).first()
如果您不想重置整个ORDER BY
子句,而只想覆盖一列顺序,那么就没有内置的方法了。谢谢,这样做了!我注意到其他答案中提到了这项技术,但我从未想到在这里使用它。