使用 SQLAlchemy 从表中删除记录

Posted 2023-04-12

【中文标题】使用 SQLAlchemy 从表中删除记录

【英文标题】：deleting records from table using SQLAlchemy

【发布时间】：2017-02-13 11:30:02

【问题描述】：

我想从测试表中删除一些数据。但即使在关注this documentation 之后，我也不确定自己做错了什么。：

hostname = 'localhost'
db_name = 'xx'
db_port = 'xx'
login = 'xx'
pwd = 'xx'

con_string = 'mysql+mysqlconnector://login:passwd@hostname:port/db'
engine_str = con_string.format(
    login=login, passwd=pwd, hostname=hostname, port=db_port, db=db_name
)

try:
    engine = sqlalchemy.create_engine(engine_str, echo=False)
    session = sessionmaker(bind=engine)
    connection = engine.connect()
    session = session(bind=connection)
    Base = declarative_base()

except exc.SQLAlchemyError:
    raise


t_packages = Table('test_table', Base.metadata, autoload_with=engine)
session.query(t_packages).filter_by(environment='sandbox').delete()

错误信息：

 line 119, in delete_package_reference_by_env
    session.query(t_packages).filter_by(environment=environment).delete()
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\query.py", line 3155, in delete
    delete_op.exec_()
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\persistence.py", line 1167, in exec_
    self._do_pre_synchronize()
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\persistence.py", line 1221, in _do_pre_synchronize
    target_cls = query._mapper_zero().class_
AttributeError: 'NoneType' object has no attribute 'class_'

【问题讨论】：

非常相关：***.com/questions/9882358/…

@IljaEverilä 我试过这个解决方案，但没有用。它返回：sqlalchemy.exc.UnboundExecutionError: This None is not directly bound to a Connection or Engine.Use the .execute() Connection 或 Engine 的方法来执行此构造。

【参考方案1】：

Solution found on this post

我不得不使用：

d = t_packages.delete(t_packages.c.environment == 'sandbox')
with engine.connect() as conn:
    conn.execute(d)