如果一个子对象有一个attribute=True，那么更新所有其他的属性为attribute=False

Question

我有以下模型:

class AddressOfUser(AddressMixin, BaseModel):
__tablename__ = 'adrusr_addressofuser'
user = db.relationship('User', backref='addresses')
user_id = db.Column(db.Integer, db.ForeignKey('users.id'), nullable=False)
default = db.Column('adrusr_default', db.Boolean, default=False)
first_name = db.Column('adrusr_first_name', db.String)
last_name = db.Column('adrusr_last_name', db.String)
phone = db.Column('adrusr_phone', db.String)

因此，当用户创建地址时，他们可以使用用于创建地址的表单中的复选框将该地址设置为默认的default属性为True。

问题是用户可以设置多个地址为默认地址这是一个问题因为我们无法知道使用哪个地址作为默认地址如果用户注册的最新地址被设置为默认地址那么其他地址将不再是默认地址我该怎么做呢?换句话说，如果的最新元素具有default = True属性，则先前的地址应该具有default = False属性。

Answer 1

可以使用"after_insert"更新兄弟对象和";after_update"事件。在下面的示例中，如果用is_default=True插入或更新地址，则事件处理程序将强制该特定用户的所有其他地址条目为is_default=False。

# https://stackoverflow.com/q/66027263/2144390
import sqlalchemy as db
from sqlalchemy import event
from sqlalchemy.orm import declarative_base, relationship
connection_uri = "sqlite://"
engine = db.create_engine(
connection_uri,
future=True,
echo=True,
)
Base = declarative_base()

class Address(Base):
__tablename__ = "address"
id = db.Column(db.Integer, primary_key=True)
user_id = db.Column(db.Integer, db.ForeignKey("user.id"), nullable=False)
address = db.Column(db.String, nullable=False)
is_default = db.Column(db.Boolean, nullable=False, default=False)
user = relationship("User", back_populates="addresses")
def __repr__(self):
return (
f"<Address(user={self.user}, address='{self.address}'"
f", is_default={self.is_default})>"
)

class User(Base):
__tablename__ = "user"
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String)
addresses = relationship("Address", back_populates="user")
def __repr__(self):
return f"<User(id={self.id}, name='{self.name}')>"

Base.metadata.create_all(engine)

def _remove_other_default_addrs(mapper, connection, target):
if target.is_default:
session = db.inspect(target).session
session.query(Address).filter(
Address.user_id == target.user_id
).filter(Address.id != target.id).filter(
Address.is_default == True
).update(
values={"is_default": False}, synchronize_session="evaluate"
)

@event.listens_for(Address, "after_insert")
def receive_after_insert(mapper, connection, target):
_remove_other_default_addrs(mapper, connection, target)

@event.listens_for(Address, "after_update")
def receive_after_update(mapper, connection, target):
_remove_other_default_addrs(mapper, connection, target)

with db.orm.Session(engine, future=True) as session:
gord = User(name="Gord")
gord_old_addr = Address(user=gord, address="123 Old Ave", is_default=True)
session.add_all([gord, gord_old_addr])
session.commit()
print(f">>> gord_old_addr.is_default is {gord_old_addr.is_default}")
# >>> gord_old_addr.is_default is True
gord_new_addr = Address(user=gord, address="567 New Blvd", is_default=True)
session.add(gord_new_addr)
session.flush()
print(">>> session flushed")
print(f">>> gord_old_addr.is_default is {gord_old_addr.is_default}")
# >>> gord_old_addr.is_default is False