unify transactional context managers

Applied consistent behavior to the use case of
calling ``.commit()`` or ``.rollback()`` inside of an existing
``.begin()`` context manager, with the addition of potentially
emitting SQL within the block subsequent to the commit or rollback.
This change continues upon the change first added in
:ticket:`6155` where the use case of calling "rollback" inside of
a ``.begin()`` contextmanager block was proposed:

* calling ``.commit()`` or ``.rollback()`` will now be allowed
without error or warning within all scopes, including
that of legacy and future :class:`_engine.Engine`, ORM
:class:`_orm.Session`, asyncio :class:`.AsyncEngine`.  Previously,
the :class:`_orm.Session` disallowed this.

* The remaining scope of the context manager is then closed;
when the block ends, a check is emitted to see if the transaction
was already ended, and if so the block returns without action.

* It will now raise **an error** if subsequent SQL of any kind
is emitted within the block, **after** ``.commit()`` or
``.rollback()`` is called.   The block should be closed as
the state of the executable object would otherwise be undefined
in this state.

Fixes: #6288
Change-Id: I8b21766ae430f0fa1ac5ef689f4c0fb19fc84336

1 files changed, 4 insertions, 2 deletions

diff --git a/lib/sqlalchemy/ext/asyncio/session.py b/lib/sqlalchemy/ext/asyncio/session.py
index d8a5673eb..1b61d6ee3 100644
--- a/lib/sqlalchemy/ext/asyncio/session.py
+++ b/lib/sqlalchemy/ext/asyncio/session.py
@@ -399,15 +399,17 @@ class AsyncSessionTransaction(StartableContext):
 
         await greenlet_spawn(self._sync_transaction().commit)
 
-    async def start(self):
+    async def start(self, is_ctxmanager=False):
         self.sync_transaction = await greenlet_spawn(
             self.session.sync_session.begin_nested
             if self.nested
             else self.session.sync_session.begin
         )
+        if is_ctxmanager:
+            self.sync_transaction.__enter__()
         return self
 
     async def __aexit__(self, type_, value, traceback):
-        return await greenlet_spawn(
+        await greenlet_spawn(
             self._sync_transaction().__exit__, type_, value, traceback
         )