SQLAlchemy CORE doc for transactions建议使用 with
上下文管理器,如下所示:
# runs a transaction
with engine.begin() as connection:
r1 = connection.execute(table1.select())
connection.execute(table1.insert(), col1=7, col2='this is some data')
或
with connection.begin() as trans:
r1 = connection.execute(table1.select())
connection.execute(table1.insert(), col1=7, col2='this is some data')
无论哪种方式,我如何知道事务是否已执行和提交,或者是否已回滚?
最佳答案
如果它没有提出,它 promise 。如果您查看文档,您会注意到 with 语句或多或少等同于:
connection = engine.connect()
trans = connection.begin()
try:
r1 = connection.execute(table1.select())
connection.execute(table1.insert(), col1=7, col2='this is some data')
trans.commit()
except:
trans.rollback()
raise
关于评论:with 语句不一定是 try/except 的替代品,以防您需要异常处理——例如当您想知道事务是否回滚时。
如果您必须执行额外的清理或例如在事务回滚时记录日志,您仍然必须将 with 语句包装在 try/except 中,但您可以确定该事务之前已被处理控制从 with 语句控制的 block 传递:
try:
with ...:
...
except ...:
# rolled back
else:
# committed
您还可以选择重新引发错误,以便其他部分也可以处理它们的清理工作。当然,例如日志记录也可以由另一个上下文管理器处理:
from contextlib import contextmanager
@contextmanager
def logger(log, error_msg="Oh woe!"):
try:
yield
except:
log.exception(error_msg)
raise
...
with logger(log), connection.begin():
r1 = connection.execute(table1.select())
connection.execute(table1.insert(), col1=7, col2='this is some data')
在本例中,正如您在评论中指出的那样,本着 PEP 343 的精神,通过使用 with 语句消除或隐藏了 try/except。 :
This PEP adds a new statement "with" to the Python language to make it possible to factor out standard uses of try/finally statements.
关于python - 在 SQLAlchemy Core 中使用 `with` 上下文管理器我如何知道事务是否回滚?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/50674857/