Include the original event in /relations (#5626)

changelog.d/5626.feature

@@ -0,0 +1 @@
+Include the original event when asking for its relations.

synapse/rest/client/v2_alpha/relations.py

@@ -145,9 +145,9 @@ def on_GET(self, request, room_id, parent_id, relation_type=None, event_type=Non
             room_id, requester.user.to_string()
         )
 
-        # This checks that a) the event exists and b) the user is allowed to
-        # view it.
-        yield self.event_handler.get_event(requester.user, room_id, parent_id)
+        # This gets the original event and checks that a) the event exists and
+        # b) the user is allowed to view it.
+        event = yield self.event_handler.get_event(requester.user, room_id, parent_id)
 
         limit = parse_integer(request, "limit", default=5)
         from_token = parse_string(request, "from")
@@ -173,10 +173,12 @@ def on_GET(self, request, room_id, parent_id, relation_type=None, event_type=Non
         )
 
         now = self.clock.time_msec()
+        original_event = yield self._event_serializer.serialize_event(event, now)
         events = yield self._event_serializer.serialize_events(events, now)
 
         return_value = result.to_dict()
         return_value["chunk"] = events
+        return_value["original_event"] = original_event
 
         defer.returnValue((200, return_value))
 

synapse/storage/relations.py

@@ -60,7 +60,7 @@ def to_dict(self):
 class RelationPaginationToken(object):
     """Pagination token for relation pagination API.
 
-    As the results are order by topological ordering, we can use the
+    As the results are in topological order, we can use the
     `topological_ordering` and `stream_ordering` fields of the events at the
     boundaries of the chunk as pagination tokens.
 

tests/rest/client/v2_alpha/test_relations.py

@@ -126,6 +126,11 @@ def test_basic_paginate_relations(self):
             channel.json_body["chunk"][0],
         )
 
+        # We also expect to get the original event (the id of which is self.parent_id)
+        self.assertEquals(
+            channel.json_body["original_event"]["event_id"], self.parent_id
+        )
+
         # Make sure next_batch has something in it that looks like it could be a
         # valid token.
         self.assertIsInstance(