python - SQLAlchemy 属性错误 : 'property' object has no attribute 'translate'

Question

情况

用户进行购买，这些购买作为交易存储在 3 个不同的表中(取决于类型)。我需要计算女性和男性用户的交易/购买总额，因此我需要查看所有 3 个表。

为此，我在用户表中创建了一个@property:

@property
def count_credits_purchases(self):
    trans = object_session(self).query(Transaction_1).filter(Transaction_1.type == "credits").with_parent(self).count()
    trans_vk = object_session(self).query(Transaction_2).filter(Transaction_2.type == "credits").with_parent(self).count()
    trans_stripe = object_session(self).query(Transaction_3).filter(Transaction_3.type == "credits").with_parent(self).count()
    value = trans + trans_vk + trans_stripe
    return int(value)

我正在尝试使用 sqlalchemy func.sum() 计算购买总额:

total_purchases_males_credits = db_session.query(func.sum(Users.count_credits_purchases))
.filter(Users.date_added >= start_date, Users.date_added <= end_date, Users.gender == "1")
.scalar()

问题

AttributeError: 'property' object has no attribute 'translate'

translate 方法是一个字符串方法，这里发生了什么？我肯定会在 count_credits_purchases 中返回一个整数。

我做了一个测试，检查每个用户的值总是正确的:

all_users = db_session.query(Users).limit(200)
for user in all_users:
    print (user.count_credits_purchases) # gives correct result

我可以创建一个变量并在循环中计算它，但它非常低效，如果有 50k 用户，可能需要 1 小时。我需要了解如何使用 @property 属性

Answer 1

作为文档 Using Descriptors and Hybrids说你应该使用 hybrid_property以便能够在您的查询中使用它们。

看看文档中的示例:

class EmailAddress(Base):
    __tablename__ = 'email_address'

    id = Column(Integer, primary_key=True)

    # name the attribute with an underscore,
    # different from the column name
    _email = Column("email", String)

    # then create an ".email" attribute
    # to get/set "._email"
    @property
    def email(self):
        return self._email

While our EmailAddress object will shuttle the value through the email descriptor and into the _email mapped attribute, the class level EmailAddress.email attribute does not have the usual expression semantics usable with Query. To provide these, we instead use the hybrid extension