Python SQLAlchemy-为复杂混合属性创建表达式
我在Python SQLAlchemy-为复杂混合属性创建表达式,python,sqlalchemy,Python,Sqlalchemy,我在MyModel中有这样一个混合属性: @hybrid_property def state(self): states = [dummy.state_id for dummy in self.dummies.all()] if all(state == "DUMMY" for state in states): return State.query.get("DUMMY").text if all((state
MyModel
中有这样一个混合属性
:
@hybrid_property
def state(self):
states = [dummy.state_id for dummy in self.dummies.all()]
if all(state == "DUMMY" for state in states):
return State.query.get("DUMMY").text
if all((state == "FAKE" or state == "DUMMY") for state in states):
return State.query.get("FAKE").text
return State.query.get("INVALID").text
我想在我的资源中查询它,如下所示:
valid_text = State.query.get("FAKE").text
return data_layer.model.query.filter_by(state=valid_text) # Where data_layer.model is MyModel
但我得到一个空数组。只需执行data\u layer.model.query.all()
即可获取数据,从而使逻辑正常工作
我知道我可能需要为我的属性创建一个表达式
,但我发现的每个示例都是用于更简单的用例
我试过这个:
@state.expression
def state(cls):
states = [dummy.state_id for dummy in self.dummies.all()]
all_dummies = all(state == "DUMMY" for state in states)
all_fakes_or_dummies = all(
(state == "FAKE" or state == "DUMMY") for state in states
)
dummy_text = State.query.get("DUMMY").text
fake_text = State.query.get("FAKE").text
invalid_text = State.query.get("INVALID").text
return case(
[
(
all_dummies,
dummy_text,
),
(
all_fakes_or_dummies,
fake_text,
),
],
else_=invalid_text,
)
但是我的资源现在返回sqlalchemy.exc.ArgumentError:不明确的文本:False。使用“text()”函数表示SQL表达式文字,或使用“literal()”表示绑定值。
我想知道如何正确实现这个python逻辑以兼容SQLAlchemy,我想这一定是问题所在。另外,我想知道在混合属性中创建如此复杂的逻辑是否是一种好的做法。在您的情况下,基于
的查询构建应该会提供您想要的结果,同时生成易于阅读的查询
正如您所说,我试图将检查分解为一些独立的块,结果如下:
class MyModel(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String)
# ...
# Hybrid Properties
@hybrid_property
def has_only_dummies(self):
# this is not optimal as need to reiterate over all objects
states = [dummy.state_id for dummy in self.dummies.all()]
return all(state == "DUMMY" for state in states)
@hybrid_property
def has_only_dummies_or_fake(self):
# this is not optimal as need to reiterate over all objects
states = [dummy.state_id for dummy in self.dummies.all()]
return all(state in ("DUMMY", "FAKE") for state in states)
@hybrid_property
def state(self):
# could reuse other hybrid properties here, but it is not efficient at all
res = None
states = [dummy.state_id for dummy in self.dummies.all()]
if all(state == "DUMMY" for state in states):
res = "DUMMY"
elif all((state == "FAKE" or state == "DUMMY") for state in states):
res = "FAKE"
else:
res = "INVALID"
return res
# Hybrid Expressions
@has_only_dummies.expression
def has_only_dummies(cls):
subq = (
exists()
.where(Dummy.model_id == cls.id)
.where(~Dummy.state_id.in_(["DUMMY"]))
).correlate(cls)
return select([case([(subq, False)], else_=True)]).label("only_dum")
@has_only_dummies_or_fake.expression
def has_only_dummies_or_fake(cls):
subq = (
exists()
.where(Dummy.model_id == cls.id)
.where(~Dummy.state_id.in_(["DUMMY", "FAKE"]))
).correlate(cls)
return select([case([(subq, False)], else_=True)]).label("only_dum_or_fak")
@state.expression
def state(cls):
return db.case(
[
(cls.has_only_dummies, "DUMMY"),
(cls.has_only_dummies_or_fake, "FAKE"),
],
else_="INVALID",
)
在这种情况下,您可以构建如下查询,包括筛选:
q = session.query(MyModel, MyModel.has_only_dummies, MyModel.has_only_dummies_or_fake, MyModel.state)
q = session.query(MyModel, MyModel.state)
q = session.query(MyModel).filter(MyModel.state != "INVALID")
MyModel.state
并不是您想要的(它是state\u id
而不是text
),但是获取文本是另一个步骤,如果您真的需要它,它很容易实现