Python 将关系转换为查询对象

假设我在表用户和汽车之间有多对多关系

当我使用时，它工作得很好

User.query.filter_by(name='somename').all().cars

Car.query.filter_by(vin='xxxxxx').all().users

我创建了将BaseQuery转换为xml对象的函数，因此我需要从

Car.query.filter_by（vin='xxxxxx'）.all（）.users

中提取BaseQuery

---

有什么方法可以做到这一点吗？

老实说，我看不出您提供的代码示例实际上是如何工作的，因为它返回一个列表。因此，

[]用户

应该生成一个错误

在任何情况下，以下都是一些选项：

# 1: this should be fine
qry1 = Car.query.join(User, Car.users).filter(User.name=='you')

# 1: this will probably not work for you, as this is not one query, although the result is a Query instance
usr1 = User.query.filter_by(name='you').one()
qry2 = Car.query.with_parent(usr1)

# 3: you might define the relationship to be lazy='dynamic', in which case the query object instance will be returned
from sqlalchemy.orm.query import Query
class Car(Base):
    __tablename__ = 'cars'
    id = Column(Integer, primary_key=True)
    vin = Column(String(50), unique=True, nullable=False)

    users = relationship(User, secondary=user_cars, 
            #backref='cars',
            backref=backref('cars', lazy="dynamic"),
            lazy="dynamic",
            )
qry3 = Car.query.filter_by(name="you").one().cars
assert isinstance(qry3, Query)

---

请在此处查看选项3的更多信息：

老实说，我看不出您提供的代码示例实际上是如何工作的，因为它返回一个列表。因此，

[]用户

应该生成一个错误

在任何情况下，以下都是一些选项：

# 1: this should be fine
qry1 = Car.query.join(User, Car.users).filter(User.name=='you')

# 1: this will probably not work for you, as this is not one query, although the result is a Query instance
usr1 = User.query.filter_by(name='you').one()
qry2 = Car.query.with_parent(usr1)

# 3: you might define the relationship to be lazy='dynamic', in which case the query object instance will be returned
from sqlalchemy.orm.query import Query
class Car(Base):
    __tablename__ = 'cars'
    id = Column(Integer, primary_key=True)
    vin = Column(String(50), unique=True, nullable=False)

    users = relationship(User, secondary=user_cars, 
            #backref='cars',
            backref=backref('cars', lazy="dynamic"),
            lazy="dynamic",
            )
qry3 = Car.query.filter_by(name="you").one().cars
assert isinstance(qry3, Query)

有关选项3的更多信息，请参见此处：