使用Python的SQLAlchemy库,可以使用异步会话(AsyncSession)从数据库中使用AssociationProxy来进行查询,同时使用预处理方式(eager loading)来提高查询效率。
下面是一个示例代码:
from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine
from sqlalchemy.orm import declarative_base, relationship, Session
from sqlalchemy.ext.associationproxy import association_proxy
Base = declarative_base()
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
name = Column(String)
addresses = relationship("Address", back_populates="user")
all_addresses = association_proxy('addresses', 'email')
class Address(Base):
__tablename__ = 'addresses'
id = Column(Integer, primary_key=True)
email = Column(String)
user_id = Column(Integer, ForeignKey('users.id'))
user = relationship("User", back_populates="addresses")
engine = create_async_engine('postgresql+asyncpg://user:password@localhost/mydatabase')
async with engine.begin() as conn:
await conn.run_sync(Base.metadata.drop_all)
await conn.run_sync(Base.metadata.create_all)
async with AsyncSession(engine) as session:
async with session.begin():
# create objects
user1 = User(name='user1', addresses=[Address(email='address1')])
user2 = User(name='user2', addresses=[Address(email='address2'), Address(email='address3')])
user3 = User(name='user3', addresses=[Address(email='address4')])
session.add_all([user1, user2, user3])
async with session.begin():
# query objects using AssociationProxy and eager loading
users = await session.execute(
select(User).options(joinedload(User.addresses)).order_by(User.id)
)
for user in users.scalars():
print(user.name, user.all_addresses)
session: Session = session
await session.commit()
在这个示例中,我们首先定义了两个模型类User和Address,并使用了association_proxy方法来生成all_addresses属性,指向User对象下的Address表中的email属性。然后我们使用AsyncSession和create_async_engine方法创建了一个异步会话和数据库引擎,并且连接到了一个名为'mydatabase'的postgres数据库。
接着,我们在数据库中生成了模型类对应的表,并且向其中插入了一些示例数据。最后,我们查询了所有用户的所有地址,并将得到的结果输出到控制台中。
这里我们使用了options方法中的joinedload来进行预处理,这是一种方法