使用SQLAlChemy会话作为上下文管理器时,接收";属性错误:__Enter__&Quot;
问题描述
我收到带有以下内容的AttributeError: __enter__
。这与with Session(engine) as session
相关:
from sqlalchemy import create_engine
from sqlalchemy import text
from sqlalchemy.orm import Session
from sqlalchemy import MetaData
from sqlalchemy import Table, Column, Integer, String
from sqlalchemy import ForeignKey
engine = create_engine("sqlite+pysqlite:///:memory:", echo=True)
with engine.connect() as conn:
conn.execute(text("CREATE TABLE some_table (x int, y int)"))
conn.execute(text("INSERT INTO some_table (x, y) VALUES (:x, :y)"),[{"x": 1, "y": 1}, {"x": 2, "y": 4}])
with engine.begin() as conn:
conn.execute(text("INSERT INTO some_table (x, y) VALUES (:x, :y)"),[{"x": 6, "y": 8}, {"x": 9, "y": 10},
{"x": 11, "y": 12}, {"x": 13, "y": 14}])
with engine.connect() as conn:
result = conn.execute(text("Select x,y From some_table"))
for x, y in result:
print(f"x:{x} y:{y}")
stmt = text("SELECT x, y FROM some_table WHERE y > :y ORDER BY x, y").bindparams(y=6)
with Session(engine) as session:
result = session.execute(stmt)
for row in result:
print(f'x: {row.x} y: {row.y}')
我使用的是蟒蛇1.3.23附带的SQLAlChemy版本。
解决方案
通过上下文管理器运行会话构建/关闭进程,如下所示:
engine = create_engine(...)
Session = sessionmaker(bind=engine)
with Session() as session:
session.add(something)
session.commit()
在SQLAlChemy<;1.4
上不受支持。
如果您的SQLAlChemy版本为例如1.3.x
,则应改为:
engine = create_engine(...)
Session = sessionmaker(bind=engine)
session = Session()
session.add(something)
session.commit()
如果您确实想使用上下文管理器,同时又需要使用SQLAlChemy<;1.4
,您可以使用以下方法(复制自SQLAlchemy docs):
### another way (but again *not the only way*) to do it ###
from contextlib import contextmanager
@contextmanager
def session_scope():
"""Provide a transactional scope around a series of operations."""
session = Session()
try:
yield session
session.commit()
except:
session.rollback()
raise
finally:
session.close()
def run_my_program():
with session_scope() as session:
ThingOne().go(session)
ThingTwo().go(session)
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