TransactionManagmentError isn't helpful for tracking down cause

[Malcolm Box]

The error: "TransactionManagementError: An error occurred in the current transaction. You can't execute queries until the end of the 'atomic' block." thrown from django/db/backends/init.py", line 372, in validate_no_broken_transaction doesn't provide enough information to help track down the problem.

The exception is thrown if self.needs_rollback is True, but the underlying reason that self.needs_rollback has been set True has been lost, since it could have happened a long time previously.

Transactions should keep track of why needs_rollback has been set, and use that to provide a more helpful error.

Background: I'm seeing this error being thrown when a task is run on a Celery queue, but not when run manually. Since it's via Celery, dropping into the debugger is impossible, and thus I'm back to trying to dump useful debug info.

[Aymeric Augustin]

Accepting the general idea, but I'm not sure how that would work in practice.

[Simon Charette]

I guess we could track the original exception and set it as the __cause__ of the TransactionManagementError.

[David Wobrock]

Beginners often struggle understanding the root cause when a TransactionManagementError occurs.

Here's a patch ​PR

[Mariusz Felisiak <felisiak.mariusz@…>]

In 3b4a5b9f:

Fixed #23353 -- Used "raise from" when raising TransactionManagementError.

This change sets the cause attribute to raised exceptions.