sqlalchemy: AttributeError: type object 'customer' has no attribute 'invoices'

Question

我是 sqlalchemy 的新手。我可以像这样通过声明映射创建数据库表：

engine = create_engine("--engine works---")

Base = declarative_base()

class Customer(Base):
    __tablename__ = 'customer'

    customer_id = Column(Integer, primary_key=True)
    name = Column(String(30))
    email = Column(String(30))

    invoices = relationship(
        'Invoice',
        order_by="Invoice.inv_id",
        back_populates='customer',
        cascade="all, delete, delete-orphan"
    )


class Invoice(Base):
    __tablename__ = 'invoice'

    inv_id = Column(Integer, primary_key=True)
    name = Column(String(30))
    created = Column(Date)

    customer_id = Column(ForeignKey('customer.customer_id'))

    customer = relationship('Customer', back_populates='invoices')

Base.metadata.create_all(engine)

这很好。我在 customer 和 invoice 表中添加了一些数据。

到目前为止一切顺利。接下来，我会像这样在这个现有数据库上尝试 automap_base：

from sqlalchemy import select, text
from sqlalchemy.orm import declarative_base, sessionmaker
from sqlalchemy.ext.automap import automap_base


engine = create_engine('--engine works---')
Base = automap_base()
# reflect
Base.prepare(engine, reflect=True)

Customer = Base.classes.customer
Invoice = Base.classes.invoice

Session = sessionmaker(bind=engine, future=True)
session = Session()

# query invoice
stmt = select(Customer, Invoice).join(Customer.invoices).order_by(Customer.customer_id, Invoice.inv_id)
res = session.execute(stmt)

for c in res:
    print(c.customer_id)

当我运行代码时，我得到：

AttributeError: type object 'customer' has no attribute 'invoices'

在这种情况下，Customer（一侧）或Invoice（多侧）的关系我错过了什么，所以当我查询客户及其发票属性和发票时与客户属性？感谢您的帮助。

Answer 1

通过 default，automap 将通过在 lower-cased 类名后附加“_collection”来在父级中创建关系，因此名称将为 Customer.invoice_collection.

在回答这个问题时，我发现连接会在 Customer.invoice_collection 上引发 AttributeError，除非我事先对 Customer 执行查询，例如

session.execute(sa.select(Customer).where(False))

我不确定为什么会这样，但是您不一定需要连接，因为您可以直接遍历 Customer.invoice_collection，或者根据发票连接 table:

stmt = sa.select(Customer, Invoice).join(Invoice)
res = session.execute(stmt)
for c, i in res:
    print(c.customer_id, i.inv_id)

sqlalchemy: AttributeError: type object 'customer' has no attribute 'invoices'

sqlalchemy: AttributeError: type object 'customer' has no attribute 'invoices'

python

sqlalchemy

declarative

automap