Use event_auth table to get previous membership

synapse/storage/databases/main/events_bg_updates.py

@@ -1937,33 +1937,27 @@ class EventsBackgroundUpdatesStore(StreamWorkerStore, StateDeltasStore, SQLBaseS
                 return 0
 
         def _find_previous_membership_txn(
-            txn: LoggingTransaction, room_id: str, user_id: str, stream_ordering: int
+            txn: LoggingTransaction, event_id: str, user_id: str
         ) -> Tuple[str, str]:
-            # Find the previous invite/knock event before the leave event
+            # Find the previous invite/knock event before the leave event. This
+            # is done by looking at the auth events of the invite/knock and
+            # finding the corresponding membership event.
             txn.execute(
                 """
-                SELECT event_id, membership
-                FROM room_memberships
-                WHERE
-                    room_id = ?
-                    AND user_id = ?
-                    AND event_stream_ordering < ?
-                ORDER BY event_stream_ordering DESC
-                LIMIT 1
+                SELECT m.event_id, m.membership
+                FROM event_auth AS a
+                INNER JOIN room_memberships AS m ON (a.auth_id = m.event_id)
+                WHERE a.event_id = ? AND m.user_id = ?
                 """,
-                (
-                    room_id,
-                    user_id,
-                    stream_ordering,
-                ),
+                (event_id, user_id),
             )
             row = txn.fetchone()
 
             # We should see a corresponding previous invite/knock event
             assert row is not None
-            event_id, membership = row
+            previous_event_id, membership = row
 
-            return event_id, membership
+            return previous_event_id, membership
 
         # Map from (room_id, user_id) to ...
         to_insert_membership_snapshots: Dict[
@@ -2057,9 +2051,8 @@ class EventsBackgroundUpdatesStore(StreamWorkerStore, StateDeltasStore, SQLBaseS
                         await self.db_pool.runInteraction(
                             "sliding_sync_membership_snapshots_bg_update._find_previous_membership",
                             _find_previous_membership_txn,
-                            room_id,
+                            membership_event_id,
                             user_id,
-                            membership_event_stream_ordering,
                         )
                     )
 

tests/storage/test_sliding_sync_tables.py

@@ -270,9 +270,7 @@ class SlidingSyncTablesTestCaseBase(HomeserverTestCase):
         return invite_room_id, persisted_event
 
     def _retract_remote_invite_for_user(
-        self,
-        user_id: str,
-        remote_room_id: str,
+        self, user_id: str, remote_room_id: str, invite_event_id: str
     ) -> EventBase:
         """
         Create a fake invite retraction for a remote room and persist it.
@@ -285,6 +283,7 @@ class SlidingSyncTablesTestCaseBase(HomeserverTestCase):
             user_id: The person who was invited and we're going to retract the
                 invite for.
             remote_room_id: The room ID that the invite was for.
+            invite_event_id: The event ID of the invite
 
         Returns:
             The persisted leave (kick) event.
@@ -298,7 +297,7 @@ class SlidingSyncTablesTestCaseBase(HomeserverTestCase):
             "origin_server_ts": 1,
             "type": EventTypes.Member,
             "content": {"membership": Membership.LEAVE},
-            "auth_events": [],
+            "auth_events": [invite_event_id],
             "prev_events": [],
         }
 
@@ -2202,6 +2201,7 @@ class SlidingSyncTablesTestCase(SlidingSyncTablesTestCaseBase):
         remote_invite_retraction_event = self._retract_remote_invite_for_user(
             user_id=user1_id,
             remote_room_id=remote_invite_room_id,
+            invite_event_id=remote_invite_event.event_id,
         )
 
         # No one local is joined to the remote room
@@ -3549,6 +3549,7 @@ class SlidingSyncTablesBackgroundUpdatesTestCase(SlidingSyncTablesTestCaseBase):
         room_id_no_info_leave_event = self._retract_remote_invite_for_user(
             user_id=user1_id,
             remote_room_id=room_id_no_info,
+            invite_event_id=room_id_no_info_invite_event.event_id,
         )
         room_id_with_info_leave_event_response = self.helper.leave(
             room_id_with_info, user1_id, tok=user1_tok
@@ -3556,6 +3557,7 @@ class SlidingSyncTablesBackgroundUpdatesTestCase(SlidingSyncTablesTestCaseBase):
         space_room_id_leave_event = self._retract_remote_invite_for_user(
             user_id=user1_id,
             remote_room_id=space_room_id,
+            invite_event_id=space_room_id_invite_event.event_id,
         )
 
         # Clean-up the `sliding_sync_membership_snapshots` table as if the inserts did not