stream creation: Avoid stream.realm references.

We want to avoid Django going back to the database to
get a realm object that the caller already has.

It's actually currently the case that we often
pre-fetch realm objects when we get stream objects
using get_stream (using a call to select_related() with
no arguments), but that is an expensive operation that
we want to avoid going forward.

This commit prepares us to just fetch slim objects.

zerver/actions/streams.py

@@ -370,7 +370,7 @@ def send_stream_creation_events_for_private_streams(
             notify_user_ids = list(stream_users_ids - realm_admin_ids)
 
             if notify_user_ids:
-                send_stream_creation_event(stream, notify_user_ids)
+                send_stream_creation_event(realm, stream, notify_user_ids)
 
 
 def send_peer_subscriber_events(
@@ -853,6 +853,8 @@ def do_change_stream_permission(
     stream.invite_only = invite_only
     stream.history_public_to_subscribers = history_public_to_subscribers
 
+    realm = stream.realm
+
     with transaction.atomic():
         stream.save(update_fields=["invite_only", "history_public_to_subscribers", "is_web_public"])
 
@@ -871,7 +873,7 @@ def do_change_stream_permission(
             )
 
             RealmAuditLog.objects.create(
-                realm=stream.realm,
+                realm=realm,
                 acting_user=acting_user,
                 modified_stream=stream,
                 event_type=RealmAuditLog.STREAM_PROPERTY_CHANGED,
@@ -887,7 +889,7 @@ def do_change_stream_permission(
 
         if old_history_public_to_subscribers_value != stream.history_public_to_subscribers:
             RealmAuditLog.objects.create(
-                realm=stream.realm,
+                realm=realm,
                 acting_user=acting_user,
                 modified_stream=stream,
                 event_type=RealmAuditLog.STREAM_PROPERTY_CHANGED,
@@ -915,7 +917,7 @@ def do_change_stream_permission(
             )
 
             RealmAuditLog.objects.create(
-                realm=stream.realm,
+                realm=realm,
                 acting_user=acting_user,
                 modified_stream=stream,
                 event_type=RealmAuditLog.STREAM_PROPERTY_CHANGED,
@@ -950,7 +952,7 @@ def do_change_stream_permission(
         )
         non_guest_user_ids = set(active_non_guest_user_ids(stream.realm_id))
         notify_stream_creation_ids = non_guest_user_ids - old_can_access_stream_user_ids
-        send_stream_creation_event(stream, list(notify_stream_creation_ids))
+        send_stream_creation_event(realm, stream, list(notify_stream_creation_ids))
 
         # Add subscribers info to the stream object. We need to send peer_add
         # events to users who were previously subscribed to the streams as

zerver/lib/streams.py

@@ -110,9 +110,9 @@ def render_stream_description(text: str, realm: Realm) -> str:
     return markdown_convert(text, message_realm=realm, no_previews=True).rendered_content
 
 
-def send_stream_creation_event(stream: Stream, user_ids: List[int]) -> None:
+def send_stream_creation_event(realm: Realm, stream: Stream, user_ids: List[int]) -> None:
     event = dict(type="stream", op="create", streams=[stream.to_dict()])
-    send_event(stream.realm, event, user_ids)
+    send_event(realm, event, user_ids)
 
 
 def create_stream_if_needed(
@@ -172,10 +172,10 @@ def create_stream_if_needed(
             )
     if created:
         if stream.is_public():
-            send_stream_creation_event(stream, active_non_guest_user_ids(stream.realm_id))
+            send_stream_creation_event(realm, stream, active_non_guest_user_ids(stream.realm_id))
         else:
             realm_admin_ids = [user.id for user in stream.realm.get_admin_users_and_bots()]
-            send_stream_creation_event(stream, realm_admin_ids)
+            send_stream_creation_event(realm, stream, realm_admin_ids)
 
     return stream, created