sqlalchemy回滚的原因

Question

I am using sqlalchemy to store data into a postgresql database. I am a little bit confused that sqlalchemy rolls back on execution without throwing an exception. I found an article in the documentary and tried to prevent rollbacks by setting pool_reset_on_return='commit'

This actually leads sqlalchemy to do nothing. Hence, I inserted a line that explicitly calls trans.commit() that leads to the following output:

2014-03-03 18:03:33,390,p:32764 Thread-3, sqlalchemy.engine.base.Engine(_execute_context) [INFO]: INSERT INTO _fd (**)
2014-03-03 18:03:33,391,p:32764 Thread-3, sqlalchemy.engine.base.Engine(_execute_context) [INFO]: {****}
2014-03-03 18:03:33,392,p:32764 Thread-3, sqlalchemy.engine.base.Engine(__init__) [DEBUG]: Col ('fid',)
2014-03-03 18:03:33,393,p:32764 Thread-3, sqlalchemy.engine.base.Engine(process_rows) [DEBUG]: Row (*,)
2014-03-03 18:03:33,393,p:32764 Thread-3, sqlalchemy.engine.base.Engine(_rollback_impl) [INFO]: ROLLBACK

The code is quit simple so far:

1837     with conn.begin() as trans:                                                                                                                                                                                                           
1838         statement = meta.tables[_table_name].insert().values(
...
1847         )
1848         res = conn.execute(statement)
1849         trans.commit()

Does anyone have an idea, what could be the cause for the rollbacks?

Answer 1

Not 100% sure about the reason but looking at the source , we can see that when you do trans.commit() within your with.... construct, it sets the transaction to inactive. Now when the Context Manager for the transaction tries to run the __exit__() method at the end of the with statement, it triggers a rollback() because the is_active flag has been set to False. (I don't know what happens when you commit a transaction and then roll it back).

Anyways the "problem" is that with construct handles the commit and rollback part implicitly. Per the docs , all you need to do is

with conn.begin() as trans:      
    statement = meta.tables[_table_name].insert().values(
    ...
    )
    res = conn.execute(statement)

Answer 2

好的，我没有这个习惯的原因，但是在语句末尾放置conn.execute("commit")可以解决问题。