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This is a redux of #4549 with a slightly different approach: instead of always returning a 'nested' session (it's not actually nested -- more on that below), we just return the current session unless a flag is passed to specifically enable nesting. We add this flag to the few cases where a rollback is used in a `with Session() as session` block. True nested sessions are no longer supported in SQLAlchemy. Instead, when you run `session.begin_nested`, the session is flushed to the database along with the SAVEPOINT command. This allows you to run session.rollback() to go back to the savepoint. The problem is, we inspect session state for objects -- particularly via the `is_new` property. Since running session.begin_nested flushes the current session, `is_new` returns False for any objects that were pending when you made a 'nested' session. We don't want that in most cases, so we want to use nested sessions sparingly.
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This is a redux of #4549 with a slightly different approach: instead of always returning a 'nested' session (it's not actually nested -- more on that below), we just return the current session unless a flag is passed to specifically enable nesting. We add this flag to the few cases where a rollback is used in a
with Session() as sessionblock.True nested sessions are no longer supported in SQLAlchemy. Instead, when you run
session.begin_nested, the session is flushed to the database along with the SAVEPOINT command. This allows you to run session.rollback() to go back to the savepoint.The problem is, we inspect session state for objects -- particularly via the
is_newproperty. Since running session.begin_nested flushes the current session,is_newreturns False for any objects that were pending when you made a 'nested' session. We don't want that in most cases, so we want to use nested sessions sparingly.