Update alert group view receive channel filter (#2140)

We were noticing some discrepancies in alert groups counts.

From a real example:

```
# queryset is the alert groups initial queryset
>>> qs = queryset.filter(channel_filter__alert_receive_channel=arc)
>>> qs.filter(resolved_at__isnull=False).count()
1318
>>> qs = queryset.filter(channel=arc)
>>> qs.filter(resolved_at__isnull=False).count()
1356
>>> qs.filter(resolved_at__isnull=False, channel_filter__isnull=True).count()
38
```

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+### Fixed
+
+- Fix receive channel filter in alert groups API [#2140](https://github.com/grafana/oncall/pull/2140)
+
 ## v1.2.41 (2023-06-08)
 
 ### Added

engine/apps/api/tests/test_alert_group.py

@@ -43,6 +43,33 @@ def alert_group_internal_api_setup(
     return user, token, alert_groups
 
 
+@pytest.mark.django_db
+def test_get_filter_by_integration(
+    alert_group_internal_api_setup, make_alert_receive_channel, make_alert_group, make_user_auth_headers
+):
+    user, token, alert_groups = alert_group_internal_api_setup
+
+    ag = alert_groups[0]
+    # channel filter could be None, but the alert group still belongs to the original integration
+    ag.channel_filter = None
+    ag.save()
+
+    # make an alert group in other integration
+    alert_receive_channel = make_alert_receive_channel(user.organization)
+    make_alert_group(alert_receive_channel)
+
+    client = APIClient()
+    url = reverse("api-internal:alertgroup-list")
+    response = client.get(
+        url + f"?integration={ag.channel.public_primary_key}",
+        format="json",
+        **make_user_auth_headers(user, token),
+    )
+
+    assert response.status_code == status.HTTP_200_OK
+    assert len(response.data["results"]) == 4
+
+
 @pytest.mark.django_db
 def test_get_filter_started_at(alert_group_internal_api_setup, make_user_auth_headers):
     user, token, _ = alert_group_internal_api_setup

engine/apps/api/views/alert_group.py

@@ -104,7 +104,7 @@ class AlertGroupFilter(DateRangeFilterMixin, ByTeamModelFieldFilterMixin, ModelF
         method=ModelFieldFilterMixin.filter_model_field.__name__,
     )
     integration = filters.ModelMultipleChoiceFilter(
-        field_name="channel_filter__alert_receive_channel",
+        field_name="channel",
         queryset=None,
         to_field_name="public_primary_key",
         method=ModelFieldFilterMixin.filter_model_field.__name__,