Sqlalchemy异步操作不完全指北-CFANZ编程社区

异步SQLAlchemy

SQLAlchemy作为一款通用的Python Orm工具，在最近的版本也支持了异步操作。但网上很多资料都不是很齐全，API也不是很好查询的情况下，我便有了整理一份基础文档的想法。文章主要会以CRUD为入口，解决大家最基本的需求。

engine的区别

在普通的SQLAlchemy中，建立engine对象，我们会采用下面的方式:

from sqlalchemy import create_engine engine = create_engine(SQLALCHEMY_DATABASE_URI, pool_recycle=1500)

而异步的方式如下:

from sqlalchemy.ext.asyncio import create_async_engine async_engine = create_async_engine(ASYNC_SQLALCHEMY_URI, pool_recycle=1500)

session的区别

我们一般用sessionmaker来建立session，不过异步的有点区别:

from sqlalchemy.ext.asyncio import AsyncSession from sqlalchemy.orm import sessionmaker # 同步session Session = sessionmaker(engine) # 异步session 区别在于需要指定对应的class_ async_session = sessionmaker(async_engine, class_=AsyncSession)

建立会话

我们还是以代码的形式展示:

# 同步 with Session() as session: # 里面是具体的sql操作 pass # 异步 async with Session() as session: # 里面是异步的操作，区别就是从with变成了async with 也就意味着方法必须是async修饰的 pass

以上是关于建立连接，处理会话的一些区别，接着我们讲对应的CRUD操作。

查询

这里依旧会给出新老版本的对比:

# 注意Session为同步Session，为了区分，异步session为async_session # model则为具体的Model类 # 异步查询方式 from sqlalchemy import select async def query(): async with async_session() as session: sql = select(model).where(model.id == 1) print(sql) # 这里可以打印出sql result = await session.execute(sql) # 第一条数据 data = result.scalars().first() # 所有数据 # data = result.scalars().all() # 同步查询方式一 def query(): with Session() as session: # 查询id=1的第一条数据 result对应的就是model的实例如果没有则是None result = session.query(model).filter_by(id=1).first() # 查询所有数据 result对应的数据为List[model]，即model数组 # result = session.query(model).filter_by(name="zhangsan").all() # 同步查询方式二 def query(): with Session() as session: # 查询id=1的第一条数据 result对应的就是model的实例如果没有则是None result = session.query(model).filter(model.id == 1).first() # 查询所有数据 result对应的数据为List[model]，即model数组 # result = session.query(model).filter(model.name == "zhangsan").all()

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新增

这里开始就只讲异步的操作了。

async def insert(data): async with async_session() as session: async with session.begin(): session.add(data) # 刷新自带的主键 await session.flush() # 释放这个data数据 session.expunge(data) return data

先说一下session.begin，这个你可以理解为一个事务操作，当采用session的begin方法后，你可以发现我们不需要调用commit方法也能把修改存入数据库。

expunge方法，是用例释放这个实例，SQLAlchemy有个特点，当你的session会话结束以后，它会销毁你插入的这种临时数据，你再想访问这个data就访问不了了。所以我们可以释放这个数据。（expunge的作用）

编辑

一般编辑有2种方式:

查询出对应的数据，在数据上修改
根据key-value的形式，修改对应数据的字段

from sqlalchemy import select, update # 方式一 async def update_record(model): async with async_session() as session: async with session.begin(): result = await session.execute(select(model).where(id=1)) now = result.scalars().first() if now is None: raise Exception("记录不存在") now.name = "李四" now.age = 23 # 这里测试过，如果去掉flush会导致数据不更新 await session.flush() session.expunge(now) return now # 方式二 async def update_by_map(): async with async_session() as session: async with session.begin(): # 更新id为1的数据，并把name改为李四 age改为23 sql = update(model).where(model.id == 1).values(name="李四", age=23) await session.execute(sql)

删除

删除的话，软删除大家都是update，所以不需要多说，物理删除的话，也有两种方式:

查到以后删除之
直接根据条件删除（这种我没有仔细研究，我选的是第一种方式，容错率高点）

async def delete_by_id(): async with async_session() as session: async with session.begin(): result = await session.execute(select(model).where(model.id == 2)) original = result.scalars().first() if original is None: raise Exception("记录不存在") # 如果是多条 # session.delete(original) # for item in result: # session.delete(item)

今天的异步内容就整理到这里，我个人觉得还是很实用的，希望对大家有帮助~~~