Inconsistency in handling of managed/unmanaged transactions
|Reported by:||mwrobel||Owned by:||aaugustin|
|Component:||Database layer (models, ORM)||Version:||1.2|
|Has patch:||no||Needs documentation:||no|
|Needs tests:||no||Patch needs improvement:||no|
I think that there are some bugs in the way the 'managed' flag is handled in enter_transaction_management() and leave_transaction_management() in django/db/transaction.py.
- enter_transaction_management() has a 'managed' parameter. I guess it should set the new transaction in managed mode depending on the value of this parameter, but it takes the mode from the surrounding transaction or from the settings (as stated in a comment). Surprisingly, connection._enter_transaction_management() is called with the value of the 'managed' parameter instead of the mode that is set for the new transaction.
- leave_transaction_management() calls connection._leave_transaction_management() passing the mode of the current transaction (the transaction that is being left) as a parameter. From what I can see in django/db/backends/postgresql_psycopg2/base.py, it expects to get the mode of the transaction that will be active after leave_transaction_management() finishes.
Now I will describe the use case in which I encountered the problems: I use the psycopg2 backend and I want to have the connection in database-level autocommit mode by default. Sometimes I want to begin a managed transaction and after some operations commit or rollback it and return to the database-level autocommit mode.
Currently I have to enter the transaction as follows:
I think that the managed() calls should be redundant, but the first/second one is needed to circumvent the first/second problem I mentioned.
My proposal is to:
- change enter_transaction_management() to set mode depending on the parameter (and when parameter is not given, take the mode from the surrounding transaction or the settings).
- change leave_transaction_management() to pass the mode of the transaction that becomes active to connection._leave_transaction_management() (I don't know what was the intended semantics, but it is what pycopg2 backend seems to expect, and other backends don't override _leave_transaction_management()).
I see that the proposed changes can break backward compatibility, but I think that they don't change any documented behavior.
I can create patches that fix the problem, but I would like to hear from Django developers if the fix is acceptable before I write the patches.
Change History (6)
comment:1 Changed 5 years ago by russellm
- Needs documentation unset
- Needs tests unset
- Patch needs improvement unset
- Triage Stage changed from Unreviewed to Accepted
comment:5 Changed 3 years ago by aaugustin
- Owner changed from nobody to aaugustin
- Status changed from new to assigned