1 files changed, 74 insertions, 2 deletions
diff --git a/synapse/storage/state.py b/synapse/storage/state.py
index ef65929bb2..6ddc4055d2 100644
--- a/synapse/storage/state.py
+++ b/synapse/storage/state.py
@@ -428,14 +428,54 @@ class StateGroupWorkerStore(EventsWorkerStore, SQLBaseStore):
         """
         # for now we do this by looking at the create event. We may want to cache this
         # more intelligently in future.
+
+        # Retrieve the room's create event
+        create_event = yield self.get_create_event_for_room(room_id)
+        defer.returnValue(create_event.content.get("room_version", "1"))
+
+    @defer.inlineCallbacks
+    def get_room_predecessor(self, room_id):
+        """Get the predecessor room of an upgraded room if one exists.
+        Otherwise return None.
+
+        Args:
+            room_id (str)
+
+        Returns:
+            Deferred[unicode|None]: predecessor room id
+
+        Raises:
+            NotFoundError if the room is unknown
+        """
+        # Retrieve the room's create event
+        create_event = yield self.get_create_event_for_room(room_id)
+
+        # Return predecessor if present
+        defer.returnValue(create_event.content.get("predecessor", None))
+
+    @defer.inlineCallbacks
+    def get_create_event_for_room(self, room_id):
+        """Get the create state event for a room.
+
+        Args:
+            room_id (str)
+
+        Returns:
+            Deferred[EventBase]: The room creation event.
+
+        Raises:
+            NotFoundError if the room is unknown
+        """
         state_ids = yield self.get_current_state_ids(room_id)
         create_id = state_ids.get((EventTypes.Create, ""))
 
+        # If we can't find the create event, assume we've hit a dead end
         if not create_id:
-            raise NotFoundError("Unknown room")
+            raise NotFoundError("Unknown room %s" % (room_id))
 
+        # Retrieve the room's create event and return
         create_event = yield self.get_event(create_id)
-        defer.returnValue(create_event.content.get("room_version", "1"))
+        defer.returnValue(create_event)
 
     @cached(max_entries=100000, iterable=True)
     def get_current_state_ids(self, room_id):
@@ -508,6 +548,31 @@ class StateGroupWorkerStore(EventsWorkerStore, SQLBaseStore):
             _get_filtered_current_state_ids_txn,
         )
 
+    @defer.inlineCallbacks
+    def get_canonical_alias_for_room(self, room_id):
+        """Get canonical alias for room, if any
+
+        Args:
+            room_id (str)
+
+        Returns:
+            Deferred[str|None]: The canonical alias, if any
+        """
+
+        state = yield self.get_filtered_current_state_ids(room_id, StateFilter.from_types(
+            [(EventTypes.CanonicalAlias, "")]
+        ))
+
+        event_id = state.get((EventTypes.CanonicalAlias, ""))
+        if not event_id:
+            return
+
+        event = yield self.get_event(event_id, allow_none=True)
+        if not event:
+            return
+
+        defer.returnValue(event.content.get("canonical_alias"))
+
     @cached(max_entries=10000, iterable=True)
     def get_state_group_delta(self, state_group):
         """Given a state group try to return a previous group and a delta between
@@ -1257,6 +1322,7 @@ class StateStore(StateGroupWorkerStore, BackgroundUpdateStore):
     STATE_GROUP_DEDUPLICATION_UPDATE_NAME = "state_group_state_deduplication"
     STATE_GROUP_INDEX_UPDATE_NAME = "state_group_state_type_index"
     CURRENT_STATE_INDEX_UPDATE_NAME = "current_state_members_idx"
+    EVENT_STATE_GROUP_INDEX_UPDATE_NAME = "event_to_state_groups_sg_index"
 
     def __init__(self, db_conn, hs):
         super(StateStore, self).__init__(db_conn, hs)
@@ -1275,6 +1341,12 @@ class StateStore(StateGroupWorkerStore, BackgroundUpdateStore):
             columns=["state_key"],
             where_clause="type='m.room.member'",
         )
+        self.register_background_index_update(
+            self.EVENT_STATE_GROUP_INDEX_UPDATE_NAME,
+            index_name="event_to_state_groups_sg_index",
+            table="event_to_state_groups",
+            columns=["state_group"],
+        )
 
     def _store_event_state_mappings_txn(self, txn, events_and_contexts):
         state_groups = {}