Optimize GET /users internal api endpoint (#4168)

# What this PR does
Speed up `GET /users` internal api endpoint by reducing number of calls
to database

## Which issue(s) this PR closes
Related to slow schedules page issue -
https://github.com/grafana/oncall-private/issues/1552
## Checklist

- [ ] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] Added the relevant release notes label (see labels prefixed w/
`release:`). These labels dictate how your PR will
    show up in the autogenerated release notes.

engine/apps/api/serializers/user.py

@@ -88,7 +88,14 @@ class ListUserSerializer(DynamicFieldsModelSerializer, EagerLoadingMixin):
     cloud_connection_status = serializers.SerializerMethodField()
     working_hours = WorkingHoursSerializer(required=False)
 
-    SELECT_RELATED = ["telegram_verification_code", "telegram_connection", "organization", "slack_user_identity"]
+    SELECT_RELATED = [
+        "telegram_verification_code",
+        "telegram_connection",
+        "organization",
+        "slack_user_identity",
+        "mobileappauthtoken",
+        "google_oauth2_user",
+    ]
 
     class Meta:
         model = User
@@ -159,7 +166,13 @@ class ListUserSerializer(DynamicFieldsModelSerializer, EagerLoadingMixin):
         return {"default": " - ".join(default), "important": " - ".join(important)}
 
     def get_cloud_connection_status(self, obj: User) -> CloudSyncStatus | None:
-        if settings.IS_OPEN_SOURCE and live_settings.GRAFANA_CLOUD_NOTIFICATIONS_ENABLED:
+        is_open_source_with_cloud_notifications = self.context.get("is_open_source_with_cloud_notifications", None)
+        is_open_source_with_cloud_notifications = (
+            is_open_source_with_cloud_notifications
+            if is_open_source_with_cloud_notifications is not None
+            else settings.IS_OPEN_SOURCE and live_settings.GRAFANA_CLOUD_NOTIFICATIONS_ENABLED
+        )
+        if is_open_source_with_cloud_notifications:
             connector = self.context.get("connector", None)
             identities = self.context.get("cloud_identities", {})
             identity = identities.get(obj.email, None)

engine/apps/api/views/user.py

@@ -137,7 +137,13 @@ class CurrentUserView(APIView, CachedSchedulesContextMixin):
         context = self.get_serializer_context()
         context.update({"request": self.request, "format": self.format_kwarg, "view": self})
 
-        if settings.IS_OPEN_SOURCE and live_settings.GRAFANA_CLOUD_NOTIFICATIONS_ENABLED:
+        is_open_source_with_cloud_notifications = (
+            settings.IS_OPEN_SOURCE and live_settings.GRAFANA_CLOUD_NOTIFICATIONS_ENABLED
+        )
+        # set context to avoid additional requests to db
+        context["is_open_source_with_cloud_notifications"] = is_open_source_with_cloud_notifications
+
+        if is_open_source_with_cloud_notifications:
             from apps.oss_installation.models import CloudConnector, CloudUserIdentity
 
             connector = CloudConnector.objects.first()
@@ -368,7 +374,13 @@ class UserView(
         context = self.get_serializer_context()
 
         if paginate_results and (page := self.paginate_queryset(queryset)) is not None:
-            if settings.IS_OPEN_SOURCE and live_settings.GRAFANA_CLOUD_NOTIFICATIONS_ENABLED:
+            is_open_source_with_cloud_notifications = (
+                settings.IS_OPEN_SOURCE and live_settings.GRAFANA_CLOUD_NOTIFICATIONS_ENABLED
+            )
+            # set context to avoid additional requests to db
+            context["is_open_source_with_cloud_notifications"] = is_open_source_with_cloud_notifications
+
+            if is_open_source_with_cloud_notifications:
                 from apps.oss_installation.models import CloudConnector, CloudUserIdentity
 
                 if (connector := CloudConnector.objects.first()) is not None:
@@ -393,7 +405,13 @@ class UserView(
         except NotFound:
             return self.wrong_team_response()
 
-        if settings.IS_OPEN_SOURCE and live_settings.GRAFANA_CLOUD_NOTIFICATIONS_ENABLED:
+        is_open_source_with_cloud_notifications = (
+            settings.IS_OPEN_SOURCE and live_settings.GRAFANA_CLOUD_NOTIFICATIONS_ENABLED
+        )
+        # set context to avoid additional requests to db
+        context["is_open_source_with_cloud_notifications"] = is_open_source_with_cloud_notifications
+
+        if is_open_source_with_cloud_notifications:
             from apps.oss_installation.models import CloudConnector, CloudUserIdentity
 
             connector = CloudConnector.objects.first()

engine/apps/mobile_app/backend.py

@@ -42,9 +42,7 @@ class MobileAppBackend(BaseMessagingBackend):
             user_active_device.delete()
 
     def serialize_user(self, user):
-        from apps.mobile_app.models import MobileAppAuthToken
-
-        return {"connected": MobileAppAuthToken.objects.filter(user=user).exists()}
+        return {"connected": getattr(user, "mobileappauthtoken", None) is not None}
 
     def notify_user(self, user, alert_group, notification_policy, critical=False):
         notify_user_about_new_alert_group.delay(